Tactical Mapping of Human Rights Abuse

Participatory Impact Pathway Analysis (PIPA)

Network Mapping can help you to learn a lot about how and why your project works the way it does. But how do you integrate the 4 steps of Net-Map (Actors, Links, Influence, Goals) into a bigger framework of monitoring and evaluation? Boru Douthwaite and his colleagues call their integrated approach Participatory Impact Pathway Analysis and while they have developed it for the impact evaluation of research projects, it’s well worth looking at it’s feasibility and usefulness for the non-research sector.

What are the similarities between gossip and the flu?

You can “give” it to many people and still keep it. This is one difference (one of the many) between gossip and money, once you give an amount of money to somebody, you don’t have it any more and you can’t give the same money to someone else.

How is this related to network mapping? I have explained the basic concepts of centrality below. These will give you a good measure for the day-to-day, implementation-oriented use of Net-Map.

However, if you are interested in getting more food for thought, and want to understand why centrality in a flu infection network should be measured differently from centrality in a money network, I’d like to recommend one of my favorite conceptual papers on social network analysis, Steve Borgatti’s “Centrality and Network Flows.”

Ask yourself first

This serves two different goals:

How does Net-Map grow (up)?

This method grows through use and discussion with users. Today I discussed possible future uses of Net-Map with fellow researchers at IFPRI and my colleague Ekin Birol asked: “So you write the research question – Who can influence XY? – on top of your Net-Map for everyone to see?”

“No, you don’t”, I said, hesitated, thought about it: “Actually, that’s a good idea, it will help everyone to stay focussed, if you add the research question as a heading to your Net-Map sheet. ”

This might sound like a detail. And it is. But the successful research and facilitation process is made up of a lot of details and all these details together make for a smooth process.


Thursday, May 17, 2012

The rational, non-expert student reader

Last week, I had a terrific teaching-related experience: At Becko's invitation, I gave a pair of teaching-related workshops at Lewis and Clark College. The first, for the faculty teaching in the college's first-year Exploration and Discovery program, addressed motivating students to read, improving their reading skills, and using assigned readings as platforms for in-class discussion and inquiry. The second discussed ways of gathering information about student learning so that we don't have to rely solely on numerical student evaluations for insight into how effective our teaching is.

A number of important themes were explored in the workshops, but I wanted to share some research and insights on two matters that seemed to strike a chord with the participants. They concern an old teaching bugaboo: student reading.
First, I tried to underscore to the workshop participants that while some students are lazy and unmotivated, students who do not read assigned material are often responding rationally to their own experience as academic readers and to how they are sometimes taught at the college and university level. This excellent summary from the University of New Mexico cites a number of reasons why students don't read:

  • They lack the background knowledge needed to understand assigned reading.
  • Their instructors give them little or no preparation for the assigned reading. (We've all had that teacher whose 'preparation' for the coming reading amounts to announcing, as students file out of the class, "We'll be discussing chapter 5 on Monday!")
  • Students don't have strategies for dealing with difficult texts in unfamiliar genres or styles.
  • The prospect of reading reminds them of past experiences where academic reading has been frustrating.
  • They do not see any causal link between reading, or reading carefully, and subsequent performance on academic tasks.
  • Last, and not only least but perhaps the biggest factor of all: We'll do their work for them, summarizing or analyzing assigned reading in class.

Given these facts, students not reading is a rational response to their situation (which doesn't excuse not reading of course). Reading is perceived as a bad investment of their intellectual time and energy. From an instructional perspective, we thus need to think about how to make reading a rational activity from the students' point of view.

This brings me to the second theme from this workshop: Faculty tend not to understand how dramatically their experience of reading differs from students'. Faculty are expert academic readers, armed with a huge body of experience and an arsenal of reading techniques and strategies that are so ingrained as to be second nature to them. I tried to illustrate this for workshop participants by having them read an unfamiliar text (here's what I chose) and then explain the strategies they used to tackle it. Not surprisingly, their strategies exemplify the habits of expert readers and stand in stark contrast to how our non-expert novice student readers approach such texts:

Novice student readers
Expert academic readers
Read once in a linear way at an invariant speed
Read multiple times, in a staggered, ‘many-geared’ way
Little interior monologue about what is being read
Make an ongoing, revisable mental draft of what is read
Easily discouraged by difficult texts, feel helpless; at most, ‘push through’ when frustrated
Have some strategies for difficult texts, ‘suspend and await clarity’
Aim is informational; focus on parts
Aim is ‘deep’ (meaning, significance); focus on whole
Do not adapt tactics to texts
Have different tactics for different texts
Tend to overmark (underline or highlight)
Light marking, annotations
Do not ‘chunk’ or give roles to parts of texts
‘Chunk,’ assign argumentative/evidential/rhetorical roles to parts of texts
Think about author questioning them
Ask questions of authors, talk back to the text
Treat authors as authorities
Treat authors as contributors to a body of knowledge or understanding

That's the second challenge: figuring out how to make our students more expert as readers. If we can motivate them to read, and help them acquire expert habits and dispositions, we would be doing them a great service. So: How can we meet these challenges readers?

  1. This is very helpful Michael. Your workshops at LC were a big hit! It is great to see institutions begin to take pedagogical development seriously.

    I think the most important thing you point out here is this: that our students are making a rational choice when they choose not to read. They aren't getting anything out of it. You give some very helpful tips about how to making reading a rational choice. I'm curious to hear ideas from others.

  2. Hello, both! Great post.

    I've started to assign a series of worksheets in courses attended by philosophical newcomers. I assign one per day, starting on the first day. They are meant to build both reading and writing skills simultaneously.

    Before I assign the first worksheet, I begin with an exercise: I hand everyone a slip of paper containing a paragraph of middling difficulty from a philosophical work. I tell the students that they have three minutes to determine how many words in the paragraph contain an A, how many contain a B, and how many contain a C. They are to write the answers elsewhere and then turn their slips face down. When the time is up, I ask them for the counts. Then I ask: What was the main point of the paragraph? Of course, more or less nobody has any idea.

    The point, which I then underscore, is that it's possible to read something carefully and take correct notes without getting anything at all from it. To succeed in philosophical reading, it is not enough to do these things. You need to read in the right way, and look for the right things. And, I explain, reading the right way will often involve stopping and thinking. But, stopping and thinking about what? Cue my lecture on what arguments are and why they are essential to figuring things out and resolving certain kinds of disputes. I really stress the fact that, if they do a reading but don't finish a reading with a clear picture of the argumentative outline and how everything fits into it, they have missed everything they needed to get out of it.

    That day, they get the first worksheet in the following sequence. I spend about ten minutes at the start of each class going over the answers.

    First worksheet: "Here is a paragraph from a recent newspaper editorial. What, in your own words, is the author's main point?" (I make this one fairly easy)

    Second worksheet: "Here are two opposing letters from the letters page of our local newspaper. What, in your own words, is the main point of each letter? What exactly is the issue on which the writers disagree? Be as precise as possible."

    Third worksheet: "What is the main point of the reading for next class? What is the author's main argument for her conclusion? Please sketch out the main argument in standard premise/conclusion form."

    Fourth worksheet: "a) What is the main point of the reading for next class? b) What is the main point of the second paragraph of page 34? c) What significance does that paragraph have for the reading overall?"

    Fifth worksheet: "The readings for next class are an article by Smith and an opposing article by Jones. What is the main issue in dispute between Smith and Jones? The first new paragraph on the third page of the Jones reading is intended as an objection against a certain argument in the Smith reading. What, in standard premise/conclusion form, is that argument from Smith, and how does the indicated paragraph in Jones constitute an objection against it?"

    Sixth worksheet: "Brown presents three different arguments against View Y. Which of these do you think is the weakest? Please write it out in premise/conclusion form, and explain how you think a defender of View Y could best object to the argument."

    If they can do the sixth worksheet, they are ready to understand the instructions for writing a good philosophy paper.


Effect of tides on mouth bar morphology and hydrodynamics

[1] Mouth bars are morphological units important for deltas, estuaries, or rivers debouching into the sea. Several processes affect the formation of these deposits. This paper focuses on the role of tides on shaping mouth bars, presenting both hydrodynamic and morphodynamic results. The effect of tides is analyzed in two end-member configurations: a river with a small tidal discharge compared to the fluvial discharge (fluvial dominated) and a river with a very large tidal discharge (tidal dominated). Mouth bar formation is analyzed using the coupled hydrodynamic and morphodynamic model Delft3D. The presence of tides influences the hydrodynamics of the jet exiting the river mouth and causes an increase in the averaged jet spreading. At low tide the lower water depth in the basin promotes a drawdown water profile in the river and an accelerated flow near the mouth. The resulting velocity field is characterized by residual currents affecting growth and final shape of the mouth bar. Simulations indicate that mouth deposits are characterized by the presence of two channels for negligible tidal discharge, whereas three principal channels are present in the tidal-dominated case, with a central channel typical of tidal inlets. On the basis of our numerical analyses, we present a robust criterion for the occurrence of mouth deposits with three channels. Trifurcations form when the tidal discharge is large with respect to the fluvial one and the tidal amplitude is small compared to the water depth. Finally, predicted mouth bar morphologies are compared with good agreement to river mouths in the Gulf of Mexico, USA.

1. Introduction

[2] Deltas result from the interaction between rivers and marine or lacustrine systems, giving rise to complex depositional patterns. Deltas are vulnerable to both anthropogenic and natural changes, such as sea level rise, variations in sediment supply, increase in storm activity and hurricane frequency, urbanization, and changes in land-use practices [e.g., Day et al., 2007; Edmonds, 2012a; Paola et al., 2011; Syvitski et al., 2009]. Human activities continuously threaten these valuable environments, and new efforts are required to improve their management and restoration strategies. A vast literature on the overall morphology of deltas is already available; however, little work has been done on the effects of tides on delta morphology, and, in particular, on the effect of tides on mouth bars development.

[3] Researchers have analyzed both large-scale structure of deltaic systems [Edmonds, 2012b; Edmonds et al., 2009, 2011a, 2011b; Edmonds and Slingerland, 2010; Canestrelli et al., 2010, Geleynse et al., 2010, 2011; Jerolmack, 2009; Jerolmack and Paola, 2007; Fagherazzi, 2008; Jerolmack and Swenson, 2007; Fagherazzi and Overeem, 2007] and their morphological units, such as mouth bars [Esposito et al., 2013; Nardin et al., 2013; Nardin and Fagherazzi, 2012; Edmonds and Slingerland, 2007; Wang, 1984; Wright, 1977; Bates, 1953].

[4] As indicated by the conceptual model of Edmonds and Slingerland [2007], when a channelized flow enters a body of water the sediment transport rate decreases and a mouth bar evolves through initial deposition, progradation, and stagnation, finally leading to channels formation and bifurcation. Esposito et al. [2013] successfully tested Edmonds and Slingerland [2007] model for mouth bar evolution by means of field data near the mouth of the Mississippi River.

[5] Deltaic bifurcations occur at the fossilized location of mouth bars, which are crucial to delta progradation and often constitute much of the deltaic system [Edmonds and Slingerland, 2009]. With increasing channel bifurcation order, there is a systematic reduction in channels length, width, and depth, due to a lower jet momentum flux and consequent lower transport distance basinward [Edmonds and Slingerland, 2007, 2009].

[6] Marine processes might play a considerable role in sediment deposition, and their influence is reflected in the diversity of planar configurations and internal stratigraphy of coastal deposits. Among others, wave energy, tidal range, and the degree to which tidal currents determine the flow within the lower reaches of a river have been indicated as important geomorphic agents for delta morphodynamics and, in particular, for mouth bar evolution [e.g., Wright and Coleman, 1974; Jerolmack, 2009; Ashton and Giosan, 2011; Geleynse et al., 2010; Nardin and Fagherazzi, 2012; Nardin et al., 2013]. As an example, the mouth bars of the Danube Delta change repeatedly, switching from a condition in which fluvial factors are predominant to a configuration in which marine processes are more relevant [Dolgopolova and Mikhailova, 2008].

[7] Nardin and Fagerazzi [2012] showed how the presence of waves leads to different bar morphologies depending on the relative importance of wave angle and wave-induced bottom shear stress. Large waves do not allow the formation of mouth bars either because of deflection of the river mouth jet, in case of oblique waves, or jet destabilization, in case of frontal waves. Wave angles between 45° and 60° have been identified as the most unfavorable for bar deposition. Nardin et al. [2013] found that waves can reduce the time of mouth bar formation and their distance from the river mouth leading to wave-induced deltas being shorter with respect to deltas experiencing no-waves conditions. According to Edmonds [2012], during the 2011 flood in Louisiana, USA, the Atchafalaya and Mississippi Rivers contributed to the same amount of land building, despite of the Mississippi River carrying a volume of sediments twice as large. This outcome was mainly due to the influence of coastal currents that can keep the sediment near the shoreline or disperse it in the ocean.

[8] Few studies have focused on the morphodynamic role of tides near river mouths; on the contrary, a rich literature is available on tidal inlets and their deposits. Since several tidal processes acting on river mouths are also present in tidal inlets, a comparison between the two systems is deemed necessary.

[9] Tidal inlets are channels maintained by tidal flow that connect the ocean with bays, lagoons, or salt marshes [e.g., FitzGerald et al., 2006]. The classical tidal inlet system consists of an ebb delta at the ocean side built around a deep central channel and two lateral shallower channels [Hayes, 1975; Fitzgerald, 1976]. The main channel is ebb dominated while the other two are flood dominated. A flood delta is also present in the bay, resulting from the combination of flood channels and tidal flats [Hayes, 1975; FitzGerald, 1976, 1996, 2006; De Swart and Zimmerman, 2008].

[10] Tidal prism and reversing tidal currents are, to a large extent, the governing forces for inlet dimensions and sediment transport dynamics. River mouths present similar dynamics but only when the tidal discharge is considerably larger than the river discharge [FitzGerald, 1996]. According to Lanzoni and Seminara [2002], even if the tidal range is small, it is still possible to have a tide dominance situation in case of large tidal prism or limited wave action.

[11] Tidal inlets are also strongly affected by external drivers, in the same way that mouth bars are. Waves, alongshore currents, and sea-level rise can have a nonnegligible influence on inlet morphology [Dissanayake et al., 2008, 2009; Lanzoni and Seminara, 2002]. It has been shown that, during periods of increasing tidal prism, the inlets of the barrier islands in the Mississippi delta evolve from a wave-dominated configuration, with broad flood deltas, to transitional forms, with sand shoals choking the mouth throat, and finally to a river mouth, with a deep main channel and a well-developed ebb delta resembling a mouth bar [Levin, 1993]. Dissanayake et al. [2009] used the numerical model Delft3D to illustrate how shore-parallel tidal currents and their time lag with respect to inlet currents have influenced the evolution of the Ameland inlet in the Dutch Wadden Sea.

[12] Numerical models are particularly suitable to understand the behavior of fluvial and deltaic systems at medium to long time scales. Among others, numerical results on delta formation by Geleynse et al. [2010, 2011] show noticeable agreement with natural systems. Their simulations include deltaic mouth bars, distributary formation, and meander-bend evolution. Numerical results from Edmonds and Slingerland [2010] suggest that deltas without vegetation, as those that formed antecedent to the Devonian period, should show more fan-like characteristics, with fewer channels and delta plain lakes. This is mainly due to the fact that vegetation operates as a cohesive agent. In fact, they show that highly cohesive sediments favor formation of bird's-foot deltas with complex floodplains and rugose shorelines. On the contrary, less cohesive sediments more likely form fan-like deltas.

[13] This work aims at analyzing concurrent effects of tides and fluvial discharge on the evolution of river mouth bars with the numerical model Delft3D. Our investigation is limited to a simple geometry and a homopycnal effluent (i.e., with negligible buoyancy); wind waves and Coriolis forces are also neglected. Two extreme cases are taken into account and discussed: (1) a river mouth with a fluvial discharge much larger than the tidal discharge and therefore characterized by unidirectional flow; (2) a river mouth with a tidal discharge much larger than the fluvial discharge, allowing the flow to reverse direction.

[14] As we are going to show, different morphologies correspond to the two aforementioned cases. Therefore, a series of additional numerical experiments with intermediate ratios of river discharge to tidal discharge are also presented in order to identify the transition from one condition to the other. The manuscript is organized as follows: in section 2 we describe the model, the model geometry, and the boundary conditions utilized in the simulations. In section 3 we present key hydrodynamic results derived from the simulations. These results are divided into (i) effect of tides on jet spreading, (ii) effect of tides on the velocity field, and (iii) residual tidal currents. Section 4 deals with the implication of the hydrodynamic results for mouth bar formation and evolution. In section 5 we qualitatively compare our results to the morphology of river mouths in the Gulf of Mexico, USA. A set of conclusions is finally presented in section 6.

2. Model Description and Setup

[15] The formation of river mouth bars is studied using the computational fluid dynamics package Delft3D [Roelvink and Van Banning, 1994; Lesser et al., 2004]. Delft3D is a numerical model composed of a number of integrated modules. Together, they allow the simulation of hydrodynamic flow, sediment transport and related bed evolution, short-wave generation and propagation, and the modeling of ecological processes and water quality parameters [Lesser, 2004]. The Delft3D-FLOW module is able to solve the unsteady shallow-water equations in two (depth-averaged) dimensions. These equations consist of the horizontal momentum equations, the continuity equation, the sediment transport equation, and a turbulence closure model. The vertical momentum equation is reduced to the hydrostatic pressure relation because vertical accelerations are assumed to be small compared to gravitational acceleration and are not taken into account [Lesser et al., 2004]. The sediment transport and morphology modules account for bed and suspended load transport of cohesive and noncohesive sediments and for the exchange of sediment between the bed and the flow. The suspended load is calculated using the advection-diffusion equation for sediments. The bed-load transport on a horizontal bed is calculated using an empirical transport formula. In the present work, the formulation proposed by Van Rijn [1993] is used. The model mesh is rectangular with rectangular cells, whose long axis is parallel to the flow (Figure 1). The simulations are designed to investigate the hydrodynamic and morphological conditions of a river discharging into a body of water with flat bottom and in the presence of tides of varying amplitude. The simulated river length (400 m) is necessarily limited in order to ensure a reasonable computational effort. Hence, a suitable landward flow discharge needs to be specified to describe the two end-member cases.

Figure 1.

Computational domain and boundary conditions.

[16] In the first, river-dominated case, a constant river discharge is assumed, such that the tidal-induced fluxes are smaller than the fluvial fluxes. In the second, tidal-dominated case, an oscillating discharge is superposed on a constant discharge, of fluvial origin, to mimic the overall discharge typical of a tidal-dominated river reach.

[17] Tidal motion in channels as well the interaction of tides with a riverine discharge is complex and difficult to be properly modeled. Factors like channel slope and shape, and bed friction can affect the velocity field [Lanzoni and Seminara, 1998; Savenije et al., 2008]. According to Lanzoni and Seminara [1998], river discharge can significantly alter tidal dynamics. For example, with an increase in riverine discharge, both the tidal wavelength and celerity decrease, while the tidal amplitude shows a more rapid upstream decay. The relationship between tidal elevation and maximum discharge depends on the nonlinear propagation of the tide in the lower reaches of the river and its floodplains. In river mouths, the tidal propagation falls somewhere between a progressive (0° of phase difference between tidal level and tidal velocity fluctuations) and standing wave (90° of phase difference). The main factors affecting the phase difference are the mouth topography and the river currents [Son and Hsu, 2011]. Savenije et al. [2008] considers the phase lag between high water and slack water as one of the main parameters for the classification of estuaries, and proposes explicit analytical and graphical solutions to determine it. Lanzoni and Seminara [1998] show how the phase lag increases with estuary convergence. Approaching the convergent limit for the estuary, the phase lag reaches 90°. Son and Hsu [2011] indicate the phase difference as a key process for the flux of sediments in the river. Accordingly, the flux of sediment is larger in the progressive wave condition.

[18] Here we assume that the tidal wave mimics a standing wave at the river mouth, so that the phase lag between high water and high water slack is zero. This assumption is valid for strongly convergent estuaries [Lanzoni and Seminara, 1998; Savenije et al., 2008], tidal inlets [Bruun et al., 1978], or for rivers with a length much smaller than the tidal wavelength. A standing wave is also the standard assumption of tidal channel hydrodynamics [Boon, 1975; Fagherazzi et al., 1999; Fagherazzi, 2008]. Thus, we neglect further elaborations connected to the contribution of both landforming discharges and propagation of the tidal signal in the fluvial reaches.

[19] In the tidal-dominated case, a constant river discharge is superimposed to an oscillating tidal discharge having a frequency of 30 deg/h (thus approximating a tidal frequency) and out of phase of 90° with respect to the water level. To impose the phase delay of 90° between discharge and water level at the river mouth we need to account for the propagation of the tide in the domain. In fact, we prescribe the water level at the seaward boundary, while the sinusoidal discharge is prescribed at the landward boundary. Since the two boundaries are distant in space a small phase lag is present.

[20] According to Lanzoni and Seminara [2002], in case of tide dominance, the volume of water exchanged in each tidal cycle is at least 1 order of magnitude larger than river discharge. Therefore, we use a discharge equal to 10% of the maximum tidal discharge in order to simulate a relative small and constant riverine flow in the tide-dominated condition.

[21] In fluvial-dominated conditions the discharge Q is 1500 m3/s. In the tidal-dominated case, the amplitude of the sinusoidal discharge is 570 m3/s. The choice of the discharge is based on the tidal inlet cross-sectional area A (m2) and tidal prism P (m3), further referred as A-P relationship. In fact, for tidal inlets field observations suggest that equilibrium exists, of the form of

display math(1)

[22] where C and q are empirical parameters [O'Brien, 1931; Jarrett, 1976; Tambroni et al., 2005; D'Alpaos et al., 2009, 2010].

[23] Specifically, Tran et al. [2012] determined the A-P relationship for a series of hypothetical inlets using the process-based model Delft3D. Based on their results, we use the values of C = 2.14 × 10−4 m2–3q and q = 0.96 in order to evaluate the tidal prism in equilibrium with the cross-sectional area of the tidal-dominated case.

[24] In the fluvial-dominated case the sediment concentration at the inflow boundary is constant, while in the tidal-dominated case we impose an equilibrium sand concentration profile. This condition means that the sediment load entering through the boundary is adapted to the local flow conditions so that neither erosion nor deposition occurs at the river mouth.

[25] For the upper and lower boundaries, we impose a zero-flux boundary condition, consisting in imposing the gradient of the alongshore water level equal to zero (Figure 1). As shown by Roelvink and Walstra [2004], in case of unknown lateral boundary conditions it is preferable to impose the water level gradient and allow the model to determine water levels and current velocities.

[26] Finally, in order to make the solution well posed, we prescribe an oscillating water level at the seaward boundary. The water level varies with a semidiurnal tidal frequency (30 deg/h) and has an amplitude ranging from 0.25 to 2.5 m. Therefore our simulations represent both microtidal and mesotidal environments.

[27] The initial condition for each simulation consists of a constant bathymetric depth (3.5 or 4.5 m) and a water level equal to mean sea level. Both sediments in the basin and sediments delivered by the river and possibly entering from the seaward boundary are noncohesive and have a specific density of 2650 kg/m3, a dry bed density of 1600 kg/m3, and a median sediment diameter D50 of 200 μm.

[28] A sensitivity analysis was performed in order to choose the proper grid size, and the results presented in this work are a good compromise between small computational time and accuracy of the solution. The grid size varies from 60 × 60 m at the margins of the basin to 20 × 60 m in the central part. The time step is set to 0.25 min. Every simulation runs for 12 model hours before starting the morphological evolution. This period is sufficient for a complete adaptation of the hydrodynamic simulation to the dynamic boundary conditions.

[29] In Delft3D, horizontal viscosity coefficients can be determined by means of two different closure models. The first is by specifying a constant or space-varying value of eddy viscosity. The second is by using a large eddy simulation model (HLES) that is added to a background value of eddy viscosity [Van Vossen, 2000; Uittenbogaard and Van Vossen, 2001]. In our simulations, we used the HLES model with a background eddy viscosity equal to 10−4 m2/s. Before adopting this value, we tested different values of background eddy viscosity, from 10−5 to 10−1 m2/s, without finding any substantial influence on the simulations results from a qualitative point of view. Moreover, we compared the results from the HLES method with those for a constant value of eddy viscosity. We used 0.1 m2/s [Van der Wegen and Roelvink, 2008], 1 m2/s [Battjes, 1975], 2 m2/s, and 5 m2/s. Also in these cases we did not find any significant qualitative difference.

[30] Bed slope affects sediment transport as indicated by Ikeda [1982]. Two coefficients are used in Delft3D in order to adjust the bed load transport in the direction of the average bed stress (longitudinal slope factor) and in the direction perpendicular to it (transverse slope factor). In the simulations, we use default values of 1 and 1.5 for longitudinal and transverse slope factors, as suggested by Ikeda [1982]. However, these parameters are uncertain and their estimates are based on small-scale experiments. For example, Van der Wegen and Roelvink [2008] suggest a value of 5 for the transverse slope factor, while Dissanayake et al. [2009] use a value of 50. According to our sensitivity analysis, the fluvial-dominated case is slightly affected by variation of either longitudinal or transverse slope factor for values up to 50. The tidal-dominated case is influenced by variations in transverse slope factor, but significant changes only occur for values larger than 20, as the central channel gradually becomes shallower and wider. These findings confirm previous results by Dissanayake et al. [2009], for which a smaller transverse slope factor leads to a narrow and deep central channel, whereas the effect of the longitudinal slope factor is negligible.

[31] In order to account for the difference in time scales between hydrodynamics and morphological evolution, bottom changes per time step are scaled up by a morphological factor [Roelvink, 2006]. The morphological factor is 15 for the fluvial-dominated case and 450 for the tidal-dominated case.

3. Hydrodynamic Results

[32] At river mouths, the width generally exceeds the depth by a factor of at least 4, and width to depth ratios greater than 50 are common [Edmonds and Slingerland, 2007]. Vertical motions of the water are usually less significant than horizontal ones and therefore the flow can be approximated with the shallow water equations [Özsoy and Ünlüata, 1982]. Note that the numerical model used in this contribution is in agreement with the shallow water approximation. As rivers empty into oceans or lakes, they expand as a confined jet, experiencing mixing, diffusion with the ambient fluid and decrease in sediment concentration and momentum. The jet is divided into two regions: the zone of flow establishment (ZOFE), having a core of constant velocity, and the zone of established flow (ZOEF), where a similarity function can be assumed for the transverse velocity profile. The transition from ZOFE to ZOEF marks the downstream location at which the turbulence generated by shearing along the margins of the jet affects the entire jet [Bates, 1953]. Jet theory has been largely used to describe rivers and inlets discharging into a standing water body [Bates, 1953; Wright and Coleman, 1974; Özsoy and Ünlüata, 1982; Wright, 1977; Rowland et al., 2010; Falcini and Jerolmack, 2010; Nardin and Fagherazzi 2012; Nardin et al., 2013].

[33] The presence of tides influences the hydrodynamic of the jet and the velocity field producing residual currents that affect the growth and the final shape of mouth bars. To study these currents, we first focus on the jet width and centerline velocity in the case of fixed bed. The self-similarity of the lateral velocity profile is assumed and the jet spreading is represented by the half width, defined as the lateral distance at which the velocity decreases to 5% of its centerline value [Özsoy, 1986]. According to Tee [1976], residual currents are the velocity field after the removal of all the sinusoidal components of tidal motion. They are time independent and can be obtained by the average over a tidal cycle. From a mathematical point of view, residual currents can be described through the fundamental equations of fluid mechanics simplified with the no-time dependence assumption [De Swart and Zimmerman, 2008; Nihoul and Ronday, 2010]. Tides can generate residual currents by several mechanisms such as nonlinear bottom friction, nonlinear terms in the continuity equation, and the nonlinear advective term in the momentum equation. Residual currents can be studied using vorticity balance, as shown by Zimmerman [1981]: in order to create residual circulations in a tidal cycle, both the production of residual tidal vorticity and a net flux of vorticity through a closed curve are necessary. Residual currents account for part of the sediment transport [Van der Vegt et al., 2006] and therefore are considered as important indicators for mouth bar morphodynamics in our study.

[34] We compute residual tidal currents by calculating the difference between the velocity field with tides, averaged in a tidal cycle, and the velocity field in the absence of tides. Thus, we depurate the flow field from the influence of the riverine discharge, and we can focus our attention on nonlinear residual currents produced by tidal motion only. Two purely hydrodynamic simulations have been run for the calculation of each residual velocity field: one with tides and the other without tides, using the same bar morphology and a nonmoving bottom.

3.1. Jet Spreading

[35] The hydrodynamics of the problem is investigated for a flat and fixed horizontal bathymetry. According to Özsoy and Ünlüata [1982], a turbulent jet in the presence of flat bottom with friction is characterized by an exponentially growth of the jet width and a decay of the centerline velocity. For large width to depth ratios, as those here considered, the ZOFE is small relatively to the ZOEF [Özsoy and Ünlüata, 1982] and, thereafter, the analysis will be restricted to the latter.

[36] To compute the velocity and jet half width in the case of flat bottom with friction, the following nondimensonal parameters are defined (Figure 2):

display math(2)

[37] where inline imageis the inlet half width, inline image is the jet half width, inline image is the inlet depth, inline imageis the water depth, inline image is the velocity, inline image is the jet velocity at the inlet, and f is the Darcy-Weisbach friction coefficient. The parameter inline image is the end coordinate for the core region and marks the passage between ZOFE and ZOEF. The solution for the unknown centerline velocity and jet half width in case of flat bottom with friction is [Özsoy and Ünlüata, 1982]

display math(3)
display math(4)
Figure 2.

Sketch of a turbulent jet exiting a river mouth.

[38] where inline image in the ZOEF and inline image and inline image are two constant values equal to 0.450 and 0.316, respectively. According to these equations, as the water depth decreases, the jet spreading increases, and the jet half width has an exponential dependence on the distance from the river mouth. For simplicity, in this work the jet half width has been approximated using a simple exponential curve of the form:

display math(5)

[39] where λ is the nondimensional e-folding length representing the spreading of the jet.

[40] The jet spreading for the river-dominated case is evaluated at different instants of the tidal cycle. The largest spreading occurs at low tide, whereas the smallest spreading corresponds to high tide (Figure 3). The mean spreading computed by averaging the spreading over several tidal cycles is larger than the spreading in the case without tides (Figure 3). This effect is present in all tested tidal amplitudes (ranging from 0.25 to 2.5 m). Moreover, the higher is the tidal range, the more evident is the increase in average spreading. This result can be explained by a nonlinear relationship between water depth and jet spreading (Figure 4a). To further investigate this aspect, the jet half width has been computed for a series of additional numerical experiments, in which a constant discharge is prescribed at the landward boundary and a constant mean water level is prescribed at the seaward boundary. The water depth varies among the experiments and Figure 4a highlights the nonlinear relationship between water depth and λ, representative of jet spreading. The e-folding length λ, calculated for different depths, is compared with the analytical solution of Özsoy and Ünlüata [1982, equation (3)], after fitting it with the simple exponential formulation adopted in equation (4).

Figure 3.

Jet half width for different tidal conditions. The points represent locations having an along inline image velocity equal to the 5% of the centerline value and have been fitted with equation (4) to obtain the solid lines. Black line: jet spreading at low tide (ht =2.5 m). Green line: jet spreading at high tide (ht=2.5 m). Blue line: averaged jet spreading in time with a tidal amplitude ht =2.5 m. Red line: jet spreading without tide.

Figure 4.

(a) The λ coefficient as a function of water depth; (b) λ coefficient as a function of the centerline velocity at the inlet boundary condition. Colored dots (Figures 4a and 4b) have been obtained with additional numerical experiments with constant discharge and variable depths (Figure 4a), or with constant depth (4.5 m) and variable discharge (Figure 4b). Continuous lines are representative of the analytical solution of Özsoy. Red dots refer to a Chezy coefficient of 45 m1/2/s, while blue dots refer to a Chezy coefficient of 30 m1/2/s. Gray arrows indicate the range of depth and velocity of the present work.

[41] We also explore the effect of friction on jet spreading. We increase friction by reducing the Chezy coefficient from 45 m1/2/s to 30 m1/2/s (Figure 4). Larger friction leads to more jet spreading, with the e-folding length λ maintaining the same trend (i.e., hyperbolic decay as a function of water depth and constant value as a function of velocity). Morphological and hydrodynamic considerations are therefore similar for different friction coefficients.

[42] The water depth in the numerical simulations ranges from 2 to 7 m, with a mean sea level at 4.5 m of depth and a maximum tidal amplitude of 2.5 m. Because the e-folding length λ does not decrease linearly with water depth (Figure 4a), it follows that

display math(6)

[43] being inline image the water depth for a generic instant of the tidal cycle, inline image a finite positive variation of depth in time, and inline image the basin depth for a fixed instant. Therefore, through a tidal cycle, the jet spreading increment during periods of low water level is more relevant than its decrease during a period of high water. As a consequence, on average, tides tend to increase jet spreading. Note also that this is true not only for our particular value of mean sea level (4.5 m) but also for any other value. In fact, λ becomes constant as h tends to infinite, and the curve is always concave upward (Figure 4a). Clearly, this effect is more relevant for larger tidal ranges and smaller depths, for which the concavity is maximum.

[44] The solution of Özsoy and Ünlüata [1982] for the normalized jet half width does not depend on jet velocity, but it is mainly affected by water depth. Figure 4b shows the jet spreading for different velocities of the river and constant water depth (i.e., in the absence of tides). As expected, the influence of velocity on jet spreading is negligible. Also in this case the analysis has been done for two different friction coefficients.

3.2. Velocity

[45] For river-dominated conditions, velocities are measured at different locations along the centerline and at different distances from the river mouth (points A–E in Figure 1). It is possible to notice a shift from a standing wave current to a progressive wave current moving from the seaward boundary toward the mouth (Figure 5). At the seaward boundary, where we impose the varying water level, the velocity is negligible at high and low tide (slack water), a typical condition of a standing wave. On the contrary, near the river mouth, the maximum flood and ebb velocities occur at high and low tide, with slack water taking place near mean sea level (progressive tidal wave) (Figures 5a and 5b).

Figure 5.

(a) Water level and (b) depth-averaged velocity in time. Different colors correspond to different distances from the inlet along the centerline. The location of the points is indicated in Figure 1 (A is the closest to the river mouth, E the farthest). (c) Phase shift between velocity and water level oscillations for points along the centerline.

[46] The transitional region between the standing wave and the progressive wave conditions can be detected through the cross correlation in time between water level and depth-averaged velocity, which determines the delay (Figure 5c). The discontinuity point indicates the transition between the two conditions.

[47] This transition is caused by the interaction between riverine discharge and seaward water level. At low tide the water depth in the basin is low, thus promoting a drawdown water profile in the river with accelerated flow near the mouth [Lamb et al., 2012]. On the contrary, as the seaward depth rises, a backwater profile establishes, with milder water gradients and limited flow acceleration near the mouth. Figure 6c shows the relationship between velocity gradient and water level in time. The velocity gradient is maximum when the water level is minimum, demonstrating the presence of an accelerated flow during periods of low water level. The velocity is therefore in phase with tidal elevation, peaking at low tide.

Figure 6.

Water surface profile along the domain centerline at (a) low tide and (b) high tide; (c) water level in time (blue line) and difference between the velocities in two points within the channel (red line), representative of the spatial velocity gradient.

3.3. Tidal Residual Velocities

[48] To determine the effect of tides on mouth hydrodynamics and bar formation we compute the tidal residual velocities by integrating the velocity field in a tidal cycle and subtracting the flow field due to the river discharge in the absence of tides [Zimmerman, 1981].

[49] In the fluvial-dominated case, the residual velocities form two lateral bands that bifurcate within a short distance from the river mouth (Figure 7). These bands are produced by an increase in spreading at low tide, which is only partly compensated by a decrease in spreading at high tide (Figure 3). A residual current is also present in the river, and it is caused by high velocities during low tide. In fact a drawdown water surface gradient establishes at low tide that accelerates the flow (Figure 6). Again this acceleration is only partly compensated by a deceleration due to the backwater effect at high tide, yielding a net residual current exiting the river.

Figure 7.

Residual currents for the fluvial-dominated case, at different stages of mouth bar formation. The tidal amplitude is 2.5 m. The isolines in each plot represent the location of the bar.

[50] In the tidal-dominated case, the residual velocity is associated with the difference between the confined flow of the turbulent jet during the ebb phase and the sink flow during the flood phase, which is radially distributed across the entire domain [Chao, 1990; Tambroni et al., 2005]. The residual velocity field displays two counterrotating vortices exiting the river mouth (Figure 8), which agrees with previous results in tidal inlets [Chao, 1990; Van der Vegt et al., 2006].

Figure 8.

Residual currents for the tidal-dominated case at different stages of mouth bar formation. The tidal amplitude is 2 m. The isolines in each plot represent the location of the bar. The two black arrows are indicative of two counterrotating eddies.

4. Bar Morphology

[51] According to Edmonds and Slingerland [2007], mouth bar formation is due to the reduction of the sediment transport rate when the turbulent jet expands into a standing body of water. More specifically, the decrease in the jet momentum flux is responsible for the formation of mouth bars. After initial deposition of sediments, the mouth bar progrades and aggrades until the depth over the bar is shallow enough to create an upstream fluid pressure that is capable of forcing the fluid around the bar rather than over the bar. The mouth bar then widens, creating a classic triangular deposit in planar view.

[52] Following the notation used by Edmonds and Slingerland [2007], h and h0 are defined as the water depth above the peak of the river mouth bar and the channel depth at the landward boundary (the water depths being referred to the mean sea level). In order to explore changes in residual currents during bar evolution, additional numerical experiments have been conducted during the growth of a bar, for ratio h/h0 equal to 0.8, 0.6, and 0.4. Successively, the morphology of the bottom was frozen, i.e., maintained constant in time, preventing the bar from growing or being demolished, and two purely hydrodynamic simulations were run, one with tides and one without them. The residual velocities are computed from the difference between the velocity averaged over a tidal cycle and the velocity without tide (Figures 7b–7d and 8b–8d). Residual velocities are found to increase when the mouth bar grows. Under dominant fluvial conditions, for example, for a tidal amplitude of 0.75 m, the maximum residual velocity is around 0.05 m/s for h/h0 = 1, and 0.15 m/s for h/h0 = 0.4.

[53] The presence of tides also promotes variations in bottom morphology. Even though fluvial conditions dominate, tides increase bar widening (Figure 9). At the beginning of bar formation, the greater is the tidal range, the higher are the residual velocities, which in turn increase sediment transport rates. Figure 10 shows longitudinal profiles of the bar for increasing tidal amplitudes. Same colors correspond to same intervals of time. It is possible to notice that the part in gray, representative of the initial stage of mouth bar formation, is higher in the presence of tides. The two lateral bands of residual velocity spread the sediments at the two sides of the river mouth and the bar immediately widens (Figure 10b). When the bar is high enough, the flow is laterally channelized during the ebb phase, when the maximum velocities occur. Hence, the bar confines the flow and favors the bifurcation process. As the magnitude of the two lateral bands of residual velocity increases, the lateral spreading grows, as well as the tendency of the bar to widen. The widening rate also starts prevailing upon the accretion rate, producing a larger but shallower bar (Figure 10). Aggradation rates therefore diminish in the final stages of bar development for large tidal amplitudes (Figure 10).

Figure 9.

Fluvial-dominated case: cumulative erosion and sedimentation for different tidal amplitudes ht after 3 days of numerical simulation and morphological factor of 15.

Figure 10.

Morphology of river mouth bars for the fluvial-dominated case. (a) Longitudinal and (b) transverse sections of river mouth bars. Each plot corresponds to a different tidal range. Same colors correspond to same temporal intervals: gray from 0 to 6 h, blue from 6 to 12 h, gray blue from 12 to 18 h, light blue from 18 to 24 h, light green from 24 to 30 h, green from 30 to 36 h, yellow from 36 to 42 h, pink from 42 to 48 h, red from 48 to 54 h, dark red from 54 to 60 h.

[54] The tidal-dominated case may be regarded as the sum of the fluvial-dominated case plus the influence of the tidal discharge. In our simulations the constant river discharge is only 10% of the maximum tidal discharge at the river mouth. However, it is enough to accelerate the process of bar growth, because of a larger sediment discharge due to the presence of the additional riverine flow, and to modify the configuration of the deposit with respect to the fluvial-dominated case. Similar to what happens in tidal inlets, the oscillating flow triggered by the tidal prism leads to the formation of a central channel (Figures 8 and 11) due to strong ebbing currents in the central part of the domain. The presence of the riverine discharge leads instead to the formation of two lateral channels, similar to the fluvial-dominated case. Different from the case of tidal inlets, the two lateral channels are ebb dominated. In fact, for tidal inlets, the basic ebb delta configuration is a central channel, dominated by ebb currents, surrounded by a swash platform and two lateral channels dominated by flood currents [FitzGerald, 1996; Davis, 1997]. In tidal inlets, flood dominance in the lateral channels is due to the different flow fields emerging in ebb and flood: while in flood phase, the flow radially distributes near the inlet and in ebb phase the flow is confined in a central jet [Tambroni et al., 2005].

Figure 11.

Tidal-dominated case, cumulative erosion and sedimentation for different tidal ranges, after 10 days of numerical simulation and morphological factor of 450; ht is the tidal amplitude.

[55] Figure 12 shows the velocity for three tidal cycles at the seaward mouth and at the right boundary. At the beginning of the simulation the system behaves as a tidal inlet. Therefore, a main central channel forms, dominated by ebb flow, and sediments are deposited at the lateral sides of the channel. Due to the formation of these initial deposits and the presence of river discharge, low slack water is delayed near the river mouth. As a result, a transitional period exists during which slack water is already reached at the right boundary, but there is still a positive flow at the river mouth. The water flows through the main channel and it is laterally deviated because of the presence of the initial deposits. During this period, the system behaves as in the fluvial-dominated case, where a constant discharge is prescribed. Moreover, since this transitional period corresponds to minimum water levels and maximum spreading, the flow is further constrained in the lateral channels with the side deposits acting as a flow barrier.

Figure 12.

Tidal-dominated case with tidal amplitude of 2.5 m. (a) Velocity variations in time at point A (green line) and point E (red line). Water level variations at point A (black line) and E (blue line). The location of the points is indicated in Figure 1 (A is the closest to the river mouth, E the farthest). Note that when the red line crosses the zero value (near the minimum in water level), the green line has still a positive value. (b) Velocity field at low water slack for height of the bar corresponding to h/h0=0.6. The isolines indicate the location of the bar. Note that peaks of velocities occur where the ebb-dominated channels form.

[56] Figure 12b shows the depth-averaged velocity field around low water slack at the right boundary for a bar elevation corresponding to h/h0 = 0.6. The maximum velocities occur in points where the lateral channels are going to form. Once the channels are incised, the confined flow occupies them during ebb, leading to a velocity higher than during flood. To sum up, while a simple bifurcation characterizes fluvial-dominated conditions, the tidal-dominated case displays three principal channels. Finally, larger tides accelerate bar growth and widen the bar deposit similar to what was observed for the fluvial-dominated case (Figures 9 and 11).

[57] To determine the transition between bifurcation (river-dominated case) and the presence of a central channel (trifurcation, tidal-dominated case), we performed a series of additional numerical experiments for two different initial basin depths (h0 = 4.5 m and h0 = 3.5 m) and two different friction coefficients (C = 45 m1/2/s and C = 30 m1/2/s). The transition is a function of the nondimensional tidal amplitude and the relative importance of tidal velocity with respect to river velocity (Figure 13). We find a robust criterion for the formation of a central channel (R2 = 93%):

display math(7)
Figure 13.

Occurrence of bifurcation or trifurcation at a river mouth as a function of nondimensional tidal amplitude and relative ratio between fluvial and tidal velocity. The green empty symbols represent trifurcations while the red-filled symbols are bifurcations. Circles C = 45 m1/2/s, h0 = 4.5 m; diamonds C = 30 m1/2/s, h0 = 4.5 m; triangles C = 45 m1/2/s, h0 = 3.5 m; squares C = 30 m1/2/s, h0 = 3.5 m. The straight green line represents the transition criterion.

[58] where u0 is the river velocity, ut the maximum tidal velocity, ht the tidal amplitude, and h0 the water depth. For a given water depth and tidal velocity, the transition from river-dominated to tidal-dominated conditions requires a small river velocity with small tides. Note that a large ratio ht/h0 maximizes the drawdown effect on river discharge, thus promoting fast shallow flows in the lateral channels and bifurcation. Moreover, for u0 > 2 ut (river discharge double the tidal discharge), the bifurcation forms independently of tidal oscillations in the basin (Figure 13). In summary, oscillations in tidally generated discharge favor the formation of a central channel, whereas tidal oscillations in the basin favor bifurcation and fluvial mouth bars.

5. Discussion

[59] Based on the results of our numerical analysis, we present the following conceptual model of bar formation under the effect of tides. In the fluvial-dominated case, tides enhance jet spreading (Figure 3), which, in turn, promotes lateral residual currents that facilitate the formation of bifurcating channels (Figure 7). Moreover, at low tide even an incipient mouth bar becomes an obstacle to the flow, given the limited water depths. As a result, more sediments are deposited on the mouth bar, speeding up its initial development (Figure 10). Once the two bifurcating channels are emplaced, strong flow establishes at low tide, magnifying the residual currents (Figure 7). These fast, shallow flows transport large quantities of sediments to the sides, creating a wider mouth bar (Figure 9).

[60] In the tidal-dominated case, the remarkable asymmetry between flood and ebb flow fields creates two residual vortexes that magnify the flow along the central axis (Figure 8). As a result, a central channel forms (Figure 11). The oscillatory flow at the mouth prevents the silting of the central channel and two deposits form at the sides (Figure 11). These deposits trigger two bifurcations and the formation of two lateral channels, also facilitated by the confined flow at low tide (Figure 12).

[61] The final bar configurations display similarities to natural systems. Figure 14 shows the mouth morphology of two rivers, the Apalachicola and Suwanee rivers in Florida, USA, with fluvial discharge and tidal features similar to those considered in this work. The Apalachicola River is fluvial dominated, with a drainage area of approximately 50,000 km2 and a mean discharge near Sumatra (FL) of 700 m3/s [U.S. Geological Survey, 2012]. The Suwanee River is tidal dominated, with a drainage area of 26,000 km2 and a mean discharge of 170 m3/s near Suwanee city (FL) [U.S. Geological Survey, 2010].

Figure 14.

(c) Locations of Apalachicola River and Suwanee River, Florida, USA. (a) Apalachicola river discharge near Sumatra, FL (USGS station 02359170; from 9 April 2012 to 12 April 2012) and (d) satellite image of Apalachicola mouth bars (29°45′N, 84°55′W). (b) Suwanee river discharge near Suwanee, FL (USGS station 02323592; from 9 May 2012 to 11 May 2012) and (e) satellite image of Suwanee mouth bars (29°17′N, 83°09′W). Data have been obtained from the annual water data report by the U.S. Geological Survey. White arrows indicate channels and white dots indicate mouth bars.

[62] The morphology of the Apalachicola mouth bars is dominated by bifurcations (Figure 14d). These landforms can thus be associated with the relatively small influence of the tidal discharge with respect to the fluvial discharge. On the contrary, in the Suwanee River, the tidal discharge seems to have a considerable role, indicated by the strong bidirectionality of the flow (Figure 14b). Here mouth bars are characterized by trifurcations, we also notice cases in which more than three channels are connected to the same node, and we ascribe this morphology to the complexity of the coastal bathymetry and variability in tidal and river discharge that were not captured in our simulations.

[63] Trifurcations do not form only in the presence of large tides; Storms et al. [2007] show that a river debouching in a deep basin can also produce a central channel. However, in their Delft3D simulations the basin is much deeper than ours, as well as deeper than Apalachicola Bay and the Suwanee river mouth. Similarly, bifurcations can also exist in tidally dominated rivers, locally favored by the complexity of the coastal landscape. Our results are therefore valid in a statistical viewpoint, with tidal-dominated rivers giving rise, on average, to more trifurcations.

[64] By modifying mouth bar morphology, tides can also affect the evolution of the entire delta. Wider and shallower bars favor vertical infilling with respect to lateral progradation. We therefore expect a prevalence of thin and spatially uniform deposits with fewer vertical discontinuities. Lack of steep gradients in mouth deposits inhibits possible avulsions, locking the distributaries in place. Wide mouth bars can also affect nearby distributaries, and fewer distributaries are needed to feed the entire delta front. Spatially extensive deposition would also maintain the mouth bars under water for a longer time, delaying vegetation encroachment and related sediment bioturbation.

[65] Our analysis has implications for future restoration projects of deltaic environments. The basic scheme for deltas restoration consists in diverting sediments from the main channel to subsiding and eroding areas where they can eventually create new wetlands [Paola et al., 2011]. According to Edmonds [2011], the success of such a restoration procedure is based on the rates of land growth estimated under different configurations of river diversion. Thus, hydrodynamic conditions of areas surrounding the river diversion are crucial to determine whether sediments would deposit near the shore or would be moved into the deep ocean. Only in the first case the diversion can effectively build new land.

[66] For the fluvial-dominated case, the presence of tides gives rise to residual currents causing the lateral spreading of sediments. These residual currents could eventually transport very fine sediment fractions far away from the river mouth and partially prevent land building. Additionally, vegetation encroachment is obstructed due to the fact that mouth bars tend to be shallower and are maintained under water for a longer time. Vegetation is generally recognized for its role in accelerating sediment deposition by means of flow deceleration and sediment trapping. As vegetation expands, detritus and fine-grained sediments mix into the soil matrix, which gradually becomes less dense, finer, and more cohesive [e.g., Feagin et al., 2009; Mariotti and Fagherazzi, 2010; Nepf, 2012].

[67] According to Edmonds [2012a], finer-graded sediments lead to the creation of new lands characterized by a rough shoreline, with small bays and fewer but larger interior lands, thus favoring trapping of incoming sediments and sheltering land from waves' erosion. Since vegetation establishment would be obstructed, all these positive feedbacks would be less effective. For the tidal-dominated case, due to the presence of the central channel, we expect the formation of more elongated deposits, with fewer but larger interior sediment islands, providing advantageous conditions for vegetation growth, encroachment, and protection from wave erosion. The aforeknown considerations suggest that tides would make sediment diversions and restoration practices less efficient in a river-dominated case, while they would favor them in the presence of a large tidal prism.

6. Conclusions

[68] Mouth bar formation is a complex phenomenon, owing to the interactions of several processes. Among others, tides play an important role in determining the final configuration of the mouth deposits. Here, the effect of tides on mouth bars has been analyzed using the computational fluid dynamics package Delft3D. The present work focuses on two end-member cases: a river with a constant and significant fluvial discharge debouching in a basin with tides (small tidal prism) and a river in which the fluvial discharge is small compared to tidal fluxes (large tidal prism).

[69] In the fluvial-dominated case, tides increase, on average, jet spreading, producing mouth bars that are wider with respect to the case without tides [e.g., Edmonds and Slingerland, 2007]. Fast flows during low tide triggered by the drawdown water surface profile [Lamb et al., 2012] transport sediments to the sides, increasing the width of the depositional area. Tidal oscillations therefore act as a dispersion process similarly to waves [Jerolmack and Swenson, 2007; Nardin and Fagherazzi, 2012; Nardin et al., 2013]. Moreover, tidal oscillations favor flow bifurcation and the formation of a central mouth deposit. In fact, even shallow deposits can become obstacles for the flow at low tide.

[70] In the tidal-dominated case, a central channel forms giving rise to a trifurcation that is commonly displayed in tidal inlets [Hayes, 1975; Fitzgerald, 1976]. Flow reversal during flood maintains the central channel flushed and produces lateral deposits that trigger two lateral bifurcations and the formation of side channels. The occurrence of a bifurcation or trifurcation depends on the relative strength of the tidal discharge with respect to the fluvial discharge and the ratio between tidal amplitude and water depth. A high fluvial discharge favors a bifurcation, which is always present for a river velocity more than twice the tidal velocity. A high tidal range at the river mouth also favor bifurcations with respect to trifurcations. Two examples from the Gulf of Mexico, USA, agree well with our findings. The Apalachicola Delta, characterized by a large fluvial discharge, is dominated by bifurcations, while the mouth of the Suwannee River, characterized by an oscillating discharge, displays on average more trifurcations.

[71] This research was supported by Exxon Mobil Upstream Research Company award EM01830, the ACS-PRF program award 51128-ND8, by NSF award OCE-0948213 and through the VCR-LTER program award DEB 0621014.


This fisherman on the shores of Lake Malawi caught only a handful of fish [Charles Mkoka]

He says the rainfall pattern has been changing over the past 40 years and blames human activity, including deforestation, for the fluctuating water levels which affect the breeding cycles of fish.

Dwindling fish stocks

Unpredictable weather

Steve Donda, Malawi's deputy director of fisheries, acknowledges that the country's fish population is in decline but says factors other than climate change, including over-fishing and the destruction of breeding environments, may be responsible.

However, a report published in June by the aid agency Oxfam, Winds of change: Climate change, poverty and the environment in Malawi, notes that winds have become so strong in the country and rains so heavy that they regularly destroy houses, crops and boats.

"The main rainy season is becoming ever-more unpredictable. In general, over the last 40 years, fishermen and farmers say temperatures are hotter and the rains are arriving late and becoming more intense and concentrated, which reduces the length of the growing season and triggers both more droughts and more floods," observes Elvis Sukali, a Lilongwe-based communications officer for Oxfam.

His comments echo those of Elina Kululanga, a climate scientist with the Climate Change and Meteorological Service - a Malawian government department responsible for weather forecasting and predictions.

"Climate variations know no boundaries and these changes are coming in because of the displacement by human emissions in the atmosphere. These are causing abnormality in the way climate behaves hence affecting rainfall patterns.

"In Malawi, we would point to temperature changes as the main factor that is linked to climate change," Kululanga says.

Taking action

Bingu wa Mutharika, Malawi's president, launches NAPA [Charles Mkoka]
Oxfam has recommended that the Malawian government compile an action list of measures it wants to implement in order to begin adapting to climate change.

Mutharika launched a nationwide plan called the National Adaptation Programmes of Action (NAPA), with the aim of improving community resilience, restoring forests, improving agricultural production and preparedness for floods and droughts and boosting climate monitoring.

Malawi's NAPAs will cost $22.43m which, to date, has not been forthcoming from the international community that initially urged Malawi to develop its plan.

Oxfam has blasted aid agencies for this, saying that the ongoing failure to fund the NAPAs drawn up by the world's least developed countries is unacceptable.

However, civil society groups in Malawi say the lack of donor funds must not become an excuse for inaction by the authorities, and are urging the government to do more even if the NAPAs remain unfunded.

'Less rain, less food'

The Malawi report coincided with Oxfam reports produced in South Africa and Uganda which revealed that the populations of these countries were facing similar challenges.

Although Africa contributes less than three per cent of global emissions, Oxfam South Africa observed that climate change poses a huge threat to development on the continent.

Scientists predict that the production of many staple foods will be seriously affected, with the average maize yield in southern Africa set to decline by as much as 30 per cent in the coming years.

The number of people without adequate access to water on the continent is predicted to triple to 600 million by 2050.

In Uganda, a government climate analysis published in December 2007, noted that the wetter areas of the country around the Lake Victoria basin, in the east and northwest, are becoming wetter.

Meteorologists and farmers report the same phenomena: in most districts, recent years have witnessed an increasingly erratic onset and cessation of the rainfall seasons, and when the rain comes it is heavier and more violent.

Farmers and pastoralists say these changes are shortening the rainy season and that the net effect is less rain and more drought or as one farmer put it: "Less rain means less food."

Coping with climate change

Environmentalists aim to raise awareness of climate change in schools [Charles Mkoka]
However, some caution is needed in interpreting these statements.

In order to manage the situation, Malawi recently followed Angola, Swaziland and Zambia by launching two new disease resistant varieties of maize - ZM 309 and ZM 523 - developed for poor farmers in drought-prone areas with infertile soils, in order to help provide some food security.

The move is part of the Drought Tolerant Maize for Africa project to give more poor farmers in sub-Saharan Africa maize varieties - a staple food among Africans - that have increased levels of drought tolerance.

Christine Mtambo, Malawi's chief agriculture officer who is responsible for crop production in the Ministry of Agriculture and Food Security, says the new varieties suit the present climate conditions because they are drought tolerant and mature fast.

Perhaps, with climate change adaptation and mitigation measures in place, fishermen like Nyangu and subsistence farmers will be able to cope with the changing climate.

But Raphael Mweninguwe, a renowned Malawi environmental columnist for the weeky newspaper Sunday Times newspaper, warns that the changing climate is a wake-up call for the people to respond to changing weather conditions by employing measures that are environmentally friendly.

He argues that there should be more awareness of climate change issues among various stakeholders within the country and beyond Malawi's borders.

Source: Al Jazeera


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Not fishing related, but one of the best ever 'reads.' [Archive] - Fly Fishing Forum

: Not fishing related, but one of the best ever 'reads.'

12-06-2003, 10:49 AM
The selfish generation
We allow marketeers to dictate our social norms - with dire results

Jenni Russell
Saturday December 6, 2003
The Guardian

A friend in a precarious industry, shattered by his third redundancy in three years, made an appointment with the local careers service to discuss other options. The adviser didn't bother to turn up for the first appointment, or for the second. There was no apology and no explanation. My friend wasn't prepared to be humiliated by asking for a third. "Just when you feel like a piece of rubbish, they treat you like one," he said.

An acquaintance on a newspaper, a tough and experienced journalist, felt so continuously unwell that her doctor decided she was going through an early menopause. Then her hypercritical and contemptuous boss moved on, and her symptoms disappeared.

One factor links many of the miseries we inflict upon one another, from anti-social behaviour to bullying at work and our encounters in public places. It is our lack of respect for others, coupled with our obsession with being treated with respect ourselves. And the less respect we encounter, the less prepared we are to offer any to anyone else. It's no longer true that most people aspire to having good manners; many just want to protect their egos in every social encounter. Conscious of our jealous sensitivity to any slight, we go out into the public arena armed only with our own willingness to be aggressive or oblivious in response.

This behaviour matters enormously because we are social animals, critically dependent on the reactions of others for our well-being. Two centuries ago the Earl of Chesterfield, writing to his son, warned him that men will forgive any quarrel or criticism, except one. They cannot tolerate being treated with contempt. Last month new scientific research demonstrated that the brain reacts to a social snub in just the same way as it does to a physical injury. In effect, by our thoughtless and self-protective behaviour, we are going through our days delivering small social injuries to one another, each one of which is felt as acutely as physical pain.

The people most vulnerable to hurt are those whose self-worth is already undermined by those around them: bullied workers, mothers who have given up work, recent immigrants, people in menial jobs. Those with the least money and the least authority are made continually aware of others' contempt. But the erosion of concern for others is taking place at all levels of society. The wealthier you are, the more protected you are from the consequences. Prosperous people can largely pay others to be nice to them. Yet they too practise and suffer from the new selfishness.

Fewer people now observe the conventions of good manners. They accept invitations, only to withdraw at the last minute when something more desirable appears. At formal events, some people are ruthless about ignoring a neighbour in favour of a more useful guest. The old idea that one had a social responsibility towards one's host or fellow guests is beginning to be replaced by a determination to maximise one's individual satisfaction, regardless of the emotional injury caused to anyone else. The values of the market are openly invading the social sphere. Why practise duty when you could make a contact or secure a gain?

The answer is that we are all diminished by this behaviour. If every social encounter is reduced to a self-marketing opportunity, we will all, at some point, be made savagely unhappy. It may work, temporarily, for the powerful and desirable. But at some time every one of us will experience failure, be perceived as dull or grow old. We all want to be valued as human beings, rather than commodities. It is the generosity and tolerance of others that makes our lives bearable.

The human, social and economic cost of our lack of mutual respect is enormous. Consider the wasted emotional energy, the destruction of confidence and creativity, and the alienation that results from it. Anxious and undermined, we hand on humiliation to others, then deplore the dissolution of social bonds. The industries that surround us will do nothing to reverse this trend. They make their money and find their audiences by appealing to our egos.

12-06-2003, 01:01 PM
Thanks for posting this Fred. We'd all be better off, both individually and collectively, if we'd only be a bit kinder to others and less insecure of our own worth.


Howard Hodgkin

Howard Hodkgin, From Memory, 2014–15, oil on wood, 27 7/8 × 33 1/8 inches (70.8 × 84.1 cm) © Howard Hodgkin. Photo by Prudence Cuming Associates Ltd.

Howard Hodgkin Listed Exhibitions (73 Kb)
Howard Hodgkin Bibliography (Selected) (111 Kb)

In exploring the very nature of painting both as cultured language and sheer expression, Hodgkin disregards the classical polarities of abstraction and representation, past and present, canvas and frame. Assertive compressed gestures, sweeping complex textures, a lush palette, and the dynamic interchange of light and dark are all traits of his distinctive signature. With their maximalist gestures and saturated colors, his more intimately scaled paintings appear jewel-like, while larger works are opulent and theatrical. With incorporated frames and painted wooden supports, they operate as both objects and images. Embracing spontaneity and directness in equal measure to the processes of reflection and capitulation, it may take a year for Hodgkin to prepare to execute a single brushstroke. The seemingly casual, urgent quality of his paintings belies the fact that most of them have been worked on for two or three years. More than ever they convey the relationship between hand, eye, and memory that drives their process, visual structure, and emotional temperature.

Howard Hodgkin was born in 1932 in London. He attended Camberwell School of Art, England, from 1949 to 1950, and Bath Academy of Art, England, from 1950 to 1954.  His first retrospective was curated by Nicholas Serota at the Museum of Modern Art, Oxford, in 1976. Since then, major museum exhibitions include “Paintings 1975 to 1995,” Metropolitan Museum of Art, New York (1995, traveled to Modern Art Museum of Fort Worth, Texas; Kunstverein für die Reinlände und Westfalen, Germany; and Hayward Gallery, London, through 1996); “Howard Hodgkin Large Paintings,” Scottish National Gallery of Modern Art, Scotland (2002); Irish Museum of Modern Art, Dublin (2006, traveled to Tate Britain, London; and Museo Nacional Centro de Arte Reina Sofía, Madrid, through 2007); “Paintings: 1992–2007,” Yale Center for British Art, Connecticut (2007, traveled to Fitzwilliam Museum, University of Cambridge, England); “Royal Elephants from Moghul India: Paintings from the Collection of Howard Hodgkin,” Ashmolean Museum, Oxford (2010); “Time and Place,” Modern Art Oxford, United Kingdom (2010, traveled to De Pont Museum of Contemporary Art, The Netherlands; and San Diego Museum of Art, California, through 2011); Fondation Bemberg, France (2013); and “Made in Mumbai,” Curator’s Gallery at Chhatrapati Shivaji Maharaj Vastu Sangrahalaya, Mumbai (2016). Hodgkin was knighted in 1992, awarded the Shakespeare Prize in Hamburg in 1997, and made a Companion of Honor in 2003.

Hodgkin currently lives and works in London.


Binge Drinking Impairs Bone Healing

Binge Drinking Impairs Bone Healing

The study by Loyola University Medical Center is providing insights into how alcohol slows healing on the cellular and molecular levels. The findings could lead to treatments to improve bone healing in alcohol abusers, and possibly non-drinkers as well.

"Many bone fractures are alcohol-related, due to car accidents, falls, shootings, etc. In addition to contributing to bone fractures, alcohol also impairs the healing process. So add this to the list of reasons why you should not abuse alcohol," said Roman Natoli, who carried the study along with John Callaci and Rachel Mauer.

The study found three ways in which alcohol impaired bone healing after a fracture. There were differences between the control group and the alcohol-exposed group in the callus, the hard bony tissue that forms around the ends of fractured bones.

In the alcohol-exposed group, the callus was less mineralised, meaning not as much bone was forming. Moreover, the bone that did form was not as strong.

The findings were presented at the American Society for Bone and Mineral Research 2013 Annual Meeting in Baltimore.


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Paper Topic:

Discuss the sthrengths and weaknesses of content and process theories of motivation

Motivation is a big influencer of productivity . Many supervisors know that what motivates employees to reach their peak performance is not easy . This is because employees respond in many ways to their jobs and their organization 's practices . Thus , a behavior that is motivated is one which is voluntarily chosen by each employee . The content approach to motivation is one that is of the assumption that individuals are motivated by the desire to fulfill inner needs . Content theories are something that is on the needs that

motivate people . On the other hand process approach to motivation is on how and why people choose particular behavior in to meet their personal goals . Process theories are on the outside influences or behaviors that people choose to meet their needs . These external or outside influences are usually available to supervisors

An example of the content approach to motivation is Maslow 's Hierarchy of Needs which has five level of needs . People go up these levels as their needs are answered . As the lower needs are satisfied , then the higher needs are activated . The most powerful employee need is that one which has not be yet satisfied . Abraham Maslow presented his needs theory in 1942 and then was published in 1954 in Motivation and Personality . This can be advantageous because the employees ' needs are answered as the person is satisfied . But it has its weakness too because it is rigid and does not cover the other small details that need to be taken into consideration when discussing motivations of people . Another content need is the Alderfer 's ERG which identified three categories of needs and its advantage is that there is the addition of the frustration-regression hypothesis that when people are not able to meet their higher level of needs , then , the next lower level needs come out Meanwhile , another one of the content theory is McClelland 's Learned Needs which divides motivation into the needs for power , affiliation and achievement . This is the theory that is more on people pursuing their goals . People like to control their situations so they take risks and get feedback on their progress . This is mainly what this content theory means . There is also the motivation for power and for affiliation all under McClelland 's Learned Needs . Content needs has advantages especially if the person is motivated internally . But if he is not motivated at all , then these content theories are of not much benefit (McClelland

Examples of the process theory Vroom 's Expectancy Model which suggests that people must choose among the alternative behaviors because they will be expecting that these behaviors will also lead to one or more desired outcomes and that the other behaviors will also bring undesirable outcomes . Expectancy states that effort will also lead to first- outcomes . Equity is the thinking of fairness which is involved in rewards given

Another process theory is the Attention , Relevance , Confidence and Satisfaction (ARCS ) Model of Motivational Design or Keller...


Titanoboa... Pt 2.

As you can probably infer by the lack blog posts, the past few months I've abstained from writing anything on this website. Yet to my surprise, the average amount of visitors has been steadily increasing over the past few months, with the post receiving the most hits being Titanoboa... OMG!

I guess people like gigantic snakes.

Even Titanoboa wasn't this big. This is why we have fiction: to fuel our ever growing need to escape the mundane.


Home  >>  Write  >>  Photography  >>  Professional Photography  >>  Macro-photography

One of photography’s greatest qualities is its ability to show us things that are either outside our normal field of vision, or that we could see if we’ve looked but usually fail to register in the hubbub of daily life. In few fields of photography are these qualities more powerfully expressed than in close-up and macro-photography, whether it is the intricate vein of a fallen leaf, or the fine hairs on the knee of an insect whose entire body would go unnoticed unless it happened to land on us.

Almost anything can be a suitable subject for close-up or macro photography. Collectors for stamps, coins and other small objects can record their examples; electronic students can photograph circuit boards, and so on; but overwhelmingly the most popular subject for close-up photos is nature. Going in close, however, presents numerous technical and aesthetic challenges.

The term “macro” is one of the most misused word in photography. For years, lens manufacturers have been using it to describe any lens that focuses slightly closer than average. In fact, what they are refer to as macro, should be called close-up. Technically speaking, a photograph cannot be considered a true macro shot until the subject is reproduced on the film at life size (1:1) or greater. You will need a small amount of special equipment for macro-photography,  but it is relatively inexpensive.

“Microphotography” is not about photographing very small objects close-up, but is in fact the process of making tiny photographic images, such as on microfilm. “Photomicrography” is the art of taking photos of things we can’t see with the human eye. You can do this by attaching your camera to the top of a microscope and shooting through it. To get the best shots you’ll need a good SLR camera for depth of field and focusing. Also, you’ll need the best lens you can afford. Prime lenses are generally more suitable than zooms for sharpness and a wider aperture. Consider the focal length of your lens. With a short (50mm) lens, you might be too close to your subject, creating shadow. A short telephoto is great, but also, ones with internal focusing is an advantage. Get a tripod if you can, to reduce camera shake and motion blur. There are accessories like a close-up diopter lens, which acts like a filter, but allows you to get closer to your subject. Extension tubes and bellows are good for focusing on subjects closely because it increases the distance between the lens and the film plane. Reversing Rings and Stacking Rings are also neat – they allow you to fit your lens on backwards, giving you a closer look.

In macro-photography, look for texture, design and pattern. You can get great shots if you get close enough to focus on a pattern on something. Also, keep in mind your depth of field: you can take a shot of the center of flower (which is crisp) while having the petals around it seemed slightly blurred. This is called a “limited depth of field” and it is achieved with longer lens at a wide aperture. They are great shots. Whatever your subject, experiment and have fun – there are so many things waiting to be photographed that you might normally not see.


Bed and Breakfast Andrea e Valentina, is located at Torre del Pozzo (Cuglieri), a village in the heart of Sardinia, and offers a cosy holiday accommodation 100 metres from the seashore, along with a friendly atmosphere for a truly unforgettable stay, surrounded by the natural beauty of the West Coast of Sardinia.
At a short walk from the marine hamlets of S’Archittu and Santa Caterina, our location is suitable for taking relaxing short trips to the main tourist attractions in the Province of Oristano: the Sinis peninsula and its gorgeous beaches; the archaeological sites of Tharros and Cornus; the villages inland, so replete with folklore and history, such as Cuglieri, Santu Lussurgiu, Fordongianus; the fishing village of Cabras and the town of Bosa, so tightly bound to the sea.


Rushing Through The Journey

“But don’t hurry the journey at all.

Better if it lasts for years,

so you’re old by the time you reach the island,

wealthy with all you’ve gained on the way,

not expecting Ithaka to make you rich.”

True Life: I’m a LOTRO Addict

-Sparling Wilson

LOTRO: A Test of Patience

– Logan W

LOTRO: The Quests Go Ever On and On

Playing Lord of the Rings Online has been interesting. For me, I have zero experience playing that type of computer game, so a lot of it is just me fumbling around, not sure where to go or what to do.
I have a lot of problems with that, actually. I can start quests, and that’s fine, but ask me to find out where to go? Man, I have problems enough getting around the city where I’ve lived for all of eight years, and you’re asking me to figure out a landscape with very few signs? Needless to say, it takes me twice as long to find a quest’s location/person than it does to finish it, despite the map and indicator icon thingies (yes, that’s a term).
I’d also prefer it if it was more interactive. I know that doesn’t really make sense, but I’d like to be able to do more, aside from click on different attacks (sorry, I’m one of the ones who prefers the shoot-em-up games).
Aside from that, however, there is a lot I find fascinating and interesting about the game. As a long time Tolkien fan, getting to see the locations that I know from the books (and from the movies) laid out on a landscape I can explore for myself is, well, awesome.
Unfortunately, there is a downside to being a Tolkien geek. Even as I explore the different areas and options, I can’t help but feel like it isn’t really the Lord of the Rings. The two don’t connect in my head.  Sure, the names are the same, and the land is made out to be Middle Earth, but it’s just not right. Can’t even put my finger on the why, but it doesn’t feel like Tolkien. And I kinda think that if Tolkien were able to see LOTRO, he’d be a bit aghast.
So, I guess the end result is that I can play the game, and I find it entertaining, but it will never be my favorite game.

Coming out of the Closet

Some people are GAME. Get over it.

I am a gamer.

-Deathly Hallowed

Team 7: Castle Joyous Plains

by: Calvin Patimeteeporn, Breon Guarino, and Aneel Henry

Book 3, Canto 1 Stanzas 20 – 30

From the forest, the PC is thrown into the midst of a small village in the plains surrounding Castle Joyous. Though the path to Castle Joyous is, indeed present, the road is blocked with construction, leaving the player at the hands of the villagers, who are in desperate need of assistance. It would seem as if the Lady of Castle Joyous, has neglected the villagers’ cries for help and has left the town completely isolated. Those townspeople with weak minds and souls have already left the town for the hedonistic castle of Lady Malecasta, leaving a handful of loyal and chaste villagers to deal with the problems. With no one to rely on, the town has fallen to a destitute state, being attacked by both wolves and bandits alike that emerge from the forest at night.
As the player enters the town past a rundown barn and two already abandoned watchtowers, the player witnesses the ruins of a once busy town square. A worried innkeeper is fretting over his dwindling food supplies that are continuously being pilfered by a wolf pack that has taken residence in an area of the forest near the town. Meanwhile, a small group of villagers are holding a meeting at the town well, discussing the bandit situation. While these villagers face these pressing matters, the rest of the village also holds a fair share of menial tasks that the townspeople cannot do alone. A small girl has lost her chickens around the town square and a young boy wishes that he could retrieve his family heirloom from one of the bandits.
While the menial tasks are up to the player to decide, the wolf and bandit situation, however cannot be left alone. Something must be done. Will the player pilfer the innkeeper’s store and blame it on the “undefeatable” wolves or will the player banish the wolves once and for all? Will the player help the bandits destroy and loot the entire village or will the player remain good and repel their advances? Regardless of choice, it would appear that after these events the road opens to Castle Joyous, allowing the player to move forward of his or her journey.
However, the player encounters a struggle between the six knights of the castle and a sole, brave knight, Redcrosse. The player must now defeat four of the six knights in order to gain entry to the next part of the journey, and gain access to the hedonistic castle that is Castle Joyous.

Main Quests:
1. The Road is Blocked (part 1)
•The player encounters road construction that obstructs the player from reaching the castle.
•The player must complete Quest 2 to proceed

2. A. The Wolves that Bite and Bandits That Catch!
•The player must talk to both the Innkeeper and the villagers meeting by the well

B1. The Wolves of the Forest
•In the forthcoming night, the player must confront the wolves that plague the Innkeeper
-Option A: Defeat the wolf pack that comes to raid the Inn’s storage (Chaste).
-Option B: Pilfer all the Inn’s store and lie to the Innkeeper and blame it on the wolves (Unchaste).

B2. Traveling Bandits
•In the forthcoming night, the player must confront the bandits.
-Option A: Kill all bandits that dare set foot in the town, expelling them forever from the village (Chaste).
-Option B: Join the bandits and raid and loot the entire town. Nothing escapes your wrath (Unchaste).

3. The Road is Blocked (part 2)
•After the Quest 2, the road is cleared and the player can move on.

4. Redcrosse and the Knights
•The player encounters Redcrosse and must defeat 4 of the 6 knights that are attacking them.
•The player is allowed entry to Castle Joyous.

Side Quests:
1. The Chickens
•The player talks to a young girl who seems to have lost her chickens.
•The player must collect all three chickens that are running around the village.
-Option A: Give back the chickens to the small girl (Chaste)
-Option B: Demand payment who in the end gives up a rare gem that has been passed down her family for years (Unchaste).

2. Lost Heirloom
•The player talks to a young boy in the square.
•The player must find and locate the heirloom which happens to be in the hands of a lone bandit near the village.
•Player must defeat the bandit.
-Option A: Return the heirloom to the boy (Chaste).
-Option B: Pretend you did not find the heirloom and keep it for yourself (Unchaste).

The Innkeeper: A worried middle-aged man in commoner clothing. Owns and operates the Inn which is plagued by wolves nightly.
The Villagers: A group of emaciated townsfolk with tattered clothing who are concerned about the future of their village with the pressing matter of bandits.
The Small Girl: A young girl with dirty and torn clothing who has lost all of her chickens.
The Small Boy: A young boy with dirty and tattered clothing with no other desire than to reclaim his family’s honor by having their stolen heirloom back in his hands.
Lone Bandit: A lone bandit in bandit attire, furs and ragged clothing. Though weak, he still poses somewhat of a threat. He has stolen the boy’s family heirloom.
Bandits: Gang of bandits dressed in furs and very aggressive. They raid the towns every night or so.
Wolf Pack: A group of 6 or so wolves that raid the Inn’s store nightly.
Redcrosse: A brave knight who refuses to succumb to Lady Malecasta’s knights and needs the player’s help to defeat them.
The Six Knights: Black knights of the Lady of the castle. Aggressive and intent on serving her.

Weaving the Threads Together


Mating system and reproductive success in eastern Pacific harbour seals

Sean A. Hayes, Fisheries Ecology Division, NMFS Southwest Fisheries Science Center, 110 Shaffer Road, Santa Cruz, CA 95060, USA. Fax: 831-420-3980; E-mail:

Harbour seals sometimes breed along inland travel corridors where females become clustered in space and time and males establish underwater acoustic display territories similar to terrestrial arenas known as resource-based leks. Under these conditions, we predicted that higher levels of polygyny would be observed than has been previously reported for this species mating in open coast environments without travel corridors. Reproductive success (RS) of 70 males was measured using 20 microsatellite DNA loci and likelihood-based paternity analysis of 136 offspring collected over 3 years. Most males were assigned either zero or one paternity with 80% confidence. The greatest number of pups assigned to one male in a season was two. Variance in RS was higher for males than females (which are biologically limited to one offspring per year) indicating low to mild polygyny. In addition, distributions of relatedness values among pups within year classes did not differ significantly from a simulated distribution with R = 0, indicating that half-siblings were uncommon. Overall, polygyny levels were low relative to terrestrial pinniped mating systems and similar to observations from a harbour seal population along an open coast. Due to large confidence intervals associated with our results, we cannot rule out the hypothesis that a travel corridor might increase the degree of polygyny skew relative to that observed in open coast environments. Habitat appeared to influence male strategies as the most successful males in open coast environments patrolled offshore, while the most successful male in this study defended a territory along the travel corridor.