Resistance and reconfiguration of natural flexible submerged vegetation in hydrodynamic river modelling

In-stream submerged macrophytes have a complex morphology and several species are not rigid, but are flexible and reconfigure along with the major flow direction to avoid potential damage at high stream velocities. However, in numerical hydrodynamic models, they are often simplified to rigid sticks. In this study hydraulic resistance of vegetation is represented by an adapted bottom friction coefficient and is calculated using an existing two layer formulation for which the input parameters were adjusted to account for (i) the temporary reconfiguration based on an empirical relationship between deflected vegetation height and upstream depth-averaged velocity, and (ii) the complex morphology of natural, flexible, submerged macrophytes. The main advantage of this approach is that it removes the need for calibration of the vegetation resistance coefficient. The calculated hydraulic roughness is an input of the hydrodynamic model Telemac 2D, this model simulates depth-averaged stream velocities in and around individual vegetation patches. Firstly, the model was successfully validated against observed data of a laboratory flume experiment with three macrophyte species at three discharges. Secondly, the effect of reconfiguration was tested by modelling an in situ field flume experiment with, and without, the inclusion of macrophyte reconfiguration. The inclusion of reconfiguration decreased the calculated hydraulic roughness which resulted in smaller spatial variations of simulated stream velocities, as compared to the model scenario without macrophyte reconfiguration. We discuss that including macrophyte reconfiguration in numerical models input, can have significant and extensive effects on the model results of hydrodynamic variables and associated ecological and geomorphological parameters

River Basin Water Quality Management Models: A State-of-the-Art Review

With the increasing human activities within river basins, the problem of water quality management is becoming increasingly important. Quality management can be achieved through control/prevention measures that have various economic and water quality implications. To facilitate the analysis of available management options, decision models are needed which represent the many facets of the problem. Such models must be capable of adequately depicting the hydrological, chemical and biological processes occurring in the river; while incorporating social, economic and political considerations within the decision framework. Management analyses can be performed using simulation, optimization, or both, depending on the management goal and the size and type of the problem. The critical issues in a management model are the nonlinearities, uncertainties, multiple pollutant nature of waste discharges, multiple objectives, and the spatial and temporal distribution of management actions. Literature on various management models were reviewed under the headings of linear, nonlinear and dynamic programming approaches; their stochastic counterparts, and combined or miscellaneous approaches. Dynamic programming was found to be an attractive methodology which can exploit the sequential decision problem pertaining to river basin water quality problems (downstream control actions do not influence water quality upstream). DP handles discrete decision variables which represent discrete management alternatives, and it is generic in the sense that both linear and non-linear water quality models expressing the relation between emissions and ambient quality levels can be incorporated. An example problem is presented which demonstrates the application of a DP-based management model to formulate least-cost strategies for the Nitra River basin in Slovakia. However, it is hardly possible for a single model to represent all the aspects of a complex decision problem. Different types of management models (e.g. deterministic vs stochastic models) have different capabilities and limitations. The only way to compensate for the deficiencies is to perform the analysis in a sensitivity style. The necessity for sensitivity analyses is further implied due to the fact that water quality problems are rather loosely formulated with respect to the quality and economic goals

Flow alteration-ecology relationships in Ozark Highland streams: Consequences for fish, crayfish and macroinvertebrate assemblages

We examined flowalteration-ecology relationships in benthic macroinvertebrate, fish, and crayfish assemblages in Ozark Highland streams, USA, over two years with contrasting environmental conditions, a drought year (2012) and a flood year (2013). We hypothesized that: 1) there would be temporal variation in flow alteration-ecology relationships between the two years, 2) flow alteration-ecology relationshipswould be stronger during the drought year vs the flood year, and 3) fish assemblages would show the strongest relationships with flow alteration. We used a quantitative richest-targeted habitat (RTH) method and a qualitative multihabitat (QMH) method to collect macroinvertebrates at 16 USGS gaged sites during both years. We used backpack electrofishing to sample fish and crayfish at 17 sites in 2012 and 11 sites in 2013.Weused redundancy analysis to relate biological response metrics, including richness, diversity, density, and community-based metrics, to flow alteration.We found temporal variation in flow alteration-ecology relationships for all taxa, and that relationships differed greatly between assemblages. We found relationships were stronger for macroinvertebrates during the drought year but not for other assemblages, and that fish assemblage relationships were not stronger than the invertebrate taxa. Magnitude of average flow, frequency of high flow, magnitude of high flow, and duration of high flow were the most important categories of flow alteration metrics across taxa. Alteration of high and average flows was more important than alteration of low flows. Of 32 important flow alteration metrics across years and assemblages, 19 were significantly altered relative to expected values. Ecological responses differed substantially between drought and flood years, and this is likely to be exacerbated with predicted climate change scenarios. Differences in flow alteration-ecology relationships among taxonomic groups and temporal variation in relationships illustrate that a complex suite of variables should be considered for effective conservation of stream communities related to flow alteration

From integrated to expedient: an adaptive framework for river basin management in developing countries

Water resource management / River basin management / Water allocation / Case studies / Africa South of Sahara / Great Ruaha River Basin

Development of the Water Potential in River Estuary (Loloan) Based on Society for the Water Conservation in Saba Coastal Village Gianyar Regency

Saba village is located in Gianyar regency near by the coastal area, which is currently ±9,176 inhabitants. Water is a major necessity for life processes on earth, which means water is very important to human life. Potential water of the river flows from upstream to downstream wasted into the sea through the river estuary. Water as the most important natural resources often had a problem in its existence of its circulation and its spreading, therefore it is necessary to conserve water. This research examines the development of water potential in the river estuary based on the society for water conservationin Saba village based on SWOT analysis. Data collected:water potential, watershed topography, Saba village management structures, environmental conditions at river estuary and beaches.Analysis of potential water data using Ribasim software. The result is the water potency in dry season 0.88 m3/s, and rain season 1.141 m3/s. The potential water in the river estuary can be developed by the society by prioritizing the society initiatives that is the ability of management and maturity of a uniform society. The society thinks, formulates, plans, implements, and evaluates the needs in the development of water potentials submitted to Saba society organizations

Capacity building for flood management in developing countries under climate change

Department Head: Luis A. Garcia.2010 Summer.Includes bibliographical references.Climate change will bring new flood threats, especially in developing countries. In addition, the contexts surrounding flood management have been shifting globally. If developing countries are to address serious flood risks caused by insufficient infrastructure and lack of legislation and enforcement programs, they must improve institutional, organizational, and individual capacities for flood management systems. The research for this dissertation explored how to alleviate flood damage and achieve sound economic growth in developing countries in the context of a global paradigm shift in flood management under climate change with a focus on capacity building. The research established a conceptual model to clarify the relationships between flood risks, elements of flood management systems, and the influence of institutional, organizational, and individual capacities on the system elements. The research also offered a tool to evaluate how capacity affects the systems and to identify the needs for capacity building. Additionally, the research established and tested capacity building methodologies for flood management in developing countries under climate change, including both principles and the procedures to implement them. Case studies in Jakarta, Indonesia and the Tokai region, Japan were analyzed to identify capacity building needs and constraints in developing countries as well as factors determining effectiveness of flood management systems. They showed that while institutional arrangements are essential for effective flood management, their effectiveness depends on the capacity to implement them. While infrastructure may mitigate flood damage, the limitations of infrastructure must be recognized and should not induce complacency. Awareness of flood threats and management by the local community is a key issue and data accessibility is fundamental to the flood management process. The conceptual model used here identified capacity-related flood management problems and their interrelationships clarified the needs for capacity building at institutional, organizational, and individual levels throughout the flood management processes. Case studies in Manila, the Philippines and the Nyando river basin, Kenya led to the following principles of capacity building for flood management in developing countries under climate change: 1. Capacity to implement both structural and non-structural measures needs to be developed, 2. All institutional, organizational, and individual capacity is crucial, 3. Leadership and decision-making capacity are more necessary under increased flood risks, and 4. Capacity to secure the 'three Es' (effectiveness, efficiency, and equity) is the key to increasing feasibility of flood management means. Then, capacity building procedures to implement the principles were formulated, which consisted of the processes of capacity assessments; integration of resources including formulation and prioritization of alternatives and implementation of priority measures; and human resources development to make the most use of the resources. The case studies also suggested that complexity of problems and levels of self-sufficiency differed between urban and rural areas regardless of the shared necessity of comprehensive capacity building. Following the recent paradigm shift on public policy and the increasing complexity and uncertainty under climate change, the requirements to identify and solve problems in a comprehensive and integrated manner are even more important. Considering that problems in developing countries are more complex and intertwined than those in developed countries, the trade-offs between the requirements for flood management and the need to cope with flood risks in developing countries take on greater urgency. Given these concerns, the research offered the tools to assess and improve flood management systems. Institutional, organizational, and individual capacity building based on appropriate problem identification and needs clarification is time-consuming yet ultimately, it is the fastest and the most inevitable road for effective flood management under climate change

Sensitivity of Flood Routing Models to Variations of Momentum Equation Coefficients and Terms (HES 41)

unpublishednot peer reviewe

Is the critical Shields stress for incipient sediment motion dependent on channel-bed slope?

Data from laboratory flumes and natural streams show that the critical Shields stress for initial sediment motion increases with channel slope, which indicates that particles of the same size are more stable on steeper slopes. This observation is contrary to standard models that predict reduced stability with increasing slope due to the added downstream gravitational force. Processes that might explain this discrepancy are explored using a simple force-balance model, including increased drag from channel walls and bed morphology, variable friction angles, grain emergence, flow aeration, and changes to the local flow velocity and turbulent fluctuations. Surprisingly, increased drag due to changes in bed morphology does not appear to be the cause of the slope dependency because both the magnitude and trend of the critical Shields stress are similar for flume experiments and natural streams, and significant variations in bed morphology in flumes is unlikely. Instead, grain emergence and changes in local flow velocity and turbulent fluctuations seem to be responsible for the slope dependency due to the coincident increase in the ratio of bed-roughness scale to flow depth (i.e., relative roughness). A model for the local velocity within the grain-roughness layer is proposed based on a 1-D eddy viscosity with wake mixing. In addition, the magnitude of near-bed turbulent fluctuations is shown to depend on the depth-averaged flow velocity and the relative roughness. Extension of the model to mixed grain sizes indicates that the coarser fraction becomes increasingly difficult to transport on steeper slopes

Photographic quantification of water quality in mixing zones

A method was developed to quantitatively delineate waste concentrations throughout waste effluent mixing zones on the basis of densitometric measurements extracted from aerial photography. A mixing zone is the extent of a receiving water body ultilized to dilute a waste discharge to a concentration characteristic of a totally mixed condition. Simultaneously-acquired color infrared photography and suspended solids water samples were used to quantitatively delineate the mixing zone resulting from the discharge of a paper mill effluent. Digital scanning microdensitometer data was used to estimate and delineate suspended solids concentrations on the basis of a semi-empirical model. Photographic photometry, when predicated on a limited amount of ground sampling, can measure and delineate mixing zone waste distributions in more detail then conventional surface measuring techniques. The method has direct application to: (1) the establishment of definite and rational water quality guidelines; (2) the development of sampling and surveillance programs for use by governmental and private agencies; and (3) the development of design and location criteria for industrial and municipal waste effluent outfalls