Lake Watershed Dynamics and Bathymetry Modeling of Rara and Begnas Lakes in Nepal

Lake evolution and its changes over time are an evident and easily measurable signal of human activities and climate change impacts in mountain regions. This study presents bathymetric modeling of permanent lakes (Begnas and Rara Lakes) located in two different geographic settings of Nepal. Moreover, temporal changes in land cover and soil erosion of the lake watersheds, as well as climatic trends around these lakes, are assessed. This study supports establishing reference sites for exploring scientific evidence on the impacts of anthropogenic and climate change on lake hydrological systems. Second-order polynomial models best represent the relationship between lake depth and volume. Rara Lake had a maximum depth of 169 m with an area of 10.52 km2 and a volume of 1013.305 million cubic meters (Mm3), whereas Begnas Lake had a maximum depth of 12.5 m with an area of 2.98 ± 0.10 km2 and a water volume of 13.539 Mm3 in the year 2019. Both lake regions are experiencing changes in temperature and rainfall. The area and volume of Rara Lake and its watershed have been relatively stable even with minimal land-cover change during the recent decades. Begnas Lake and its watershed have experienced significant changes in the last few decades. This study concludes that human activities in the Begnas Lake watersheds are the primary source of lake area variation rather than climate change.

Inventário de movimentos de massa na bacia hidrográfica do rio Mascarada/RS

Mass movements inventories play a key role to the understanding of watershed dynamics. The alteration of this dynamics occurs in the moment of failure and after it due the erosion when precipitation hits the uncovered soil at the mass movement scars. Thus, this paper has characterized these mass movements, which are classified as landslides, occurred in Mascarada´s river basin through different geomorphological parameters, as slope and curvature, and comparing shape parameters against different methodologies to determine the evaluation area. The proposed shape parameters Percentage of affected area (PAA), Drainage density of scars (Ddc) and Density of scars (Dcic) were evaluated against total area of Mascarada´s river basin, against two sub-basins and against a proposed “Area of influence”. 407 scars were mapped with an area of 2,2 km², a mean slope of 36,1° and all scars are in convergent areas. The evaluation of shape forms showed that “area of influence” improved the understanding of this mass movements magnitude. Thus, the elaboration of mass movement inventories with reliable methodologies can provide important information for the natural disaster management.

Advances and next steps exploring the role of groundwater storage in watershed variability across spatial scales

<p>Groundwater is  by far the largest unfrozen freshwater resource on the planet. Yet it is often excluded or greatly simplified in global and  continental scale models.   It’s well established that feedbacks between groundwater depth, surface runoff and land energy fluxes can influence watershed dynamics. However, we still don’t understand the large scale implications of these exchanges in evolving systems.  Advances in continental scale integrated hydrologic modeling increasingly allow us to explore these interactions across spatial scales. With large scale models we can start to quantify the total impact that groundwater surface water exchanges have on the water balance as a whole, as well as watershed dynamics.  Here I will explore the buffering effect that groundwater can have on both human and natural water stressors across the US and the physical drivers of these connections.  I will also explore the impacts of long term trends on the stability of groundwater surface water exchanges. These results demonstrate the importance of the subsurface for future hydrologic predictions, and the potential gains from improved groundwater representations large scale simulations.  While there have been great advances in large scale groundwater modeling in recent years, there is still significant need for continued community model development and intercomparison.</p>

Assessing methods for the estimation of response times of stream discharge: the role of rainfall duration

Lagtimes and times of concentration are frequently determined parameters in hydrological design and greatly aid in understanding natural watershed dynamics. In unmonitored catchments, they are usually calculated using empirical or semiempirical equations developed in other studies, without critically considering where those equations were obtained and what basic assumptions they entailed. In this study, we determined the lagtimes (LT) between the middle point of rainfall events and the discharge peaks in a watershed characterized by volcanic soils and swamp forests in southern Chile. Our results were compared with calculations from 24 equations found in the literature. The mean LT for 100 episodes was 20 hours (ranging between 0.6–58.5 hours). Most formulae that only included physiographic predictors severely underestimated the mean LT, while those including the rainfall intensity or stream velocity showed better agreement with the average value. The duration of the rainfall events related significantly and positively with LTs. Thus, we accounted for varying LTs within the same watershed by including the rainfall duration in the equations that showed the best results, consequently improving our predictions. Izzard and velocity methods are recommended, and we suggest that lagtimes and times of concentration must be locally determined with hyetograph-hydrograph analyses, in addition to explicitly considering precipitation patterns.

Light Absorption Budget in a Reservoir Cascade System with Widely Differing Optical Properties

Aquatic systems are complex systems due to the environmental pressures that lead to water quality parameter changes, and consequently, variations in optically active compounds (OAC). In cascading reservoir systems, such as the Tietê Cascade Reservoir System (TCSR), which has a length of 1100 km, the horizontal gradients are expressive due to the filtration process that is caused by the sequence of dams affecting the light absorption throughout the cascade. Our new observations showed that colored dissolved organic matter (CDOM) dominate two reservoirs; non-algae particles (NAP) dominate one, and phytoplankton dominates the other. The variability of light absorption along the cascade indicates the influence of watershed dynamics in the reservoirs as much as the flow driven by previous reservoirs. Despite the effect of the variability of light absorption, light absorption by phytoplankton strongly affects the total absorption in the four reservoirs in TCSR. The results obtained in this work may enable a better understanding of how the gradient pattern changes primary production and indicates a challenge in retrieving OAC concentrations using a bio-optical model for an entire cascade composed of different optical environments.

Assessment of water demand dynamics in Arror watershed in Elgeyo Marakwet County, Kenya

Water scarcity is a serious problem worldwide, which heightens the need to understand watershed dynamics and their impact on water quantity. The study examined water demand using the WEAP (Water Evaluation and Planning) model in the Arror watershed in Kenya. The primary sources of data included remotely sensed data and socio-economic data. The secondary data included climate, river discharge and soil data. Field surveys and questionnaires were used to collect socio-economic data. From the findings, the total annual water allocated (supply) for agriculture, domestic and livestock in the watershed was 10,333,441 m3, with the highest annual consumer being agriculture in the lower part of the catchment at 7,154,457 m3 for the reference scenario (1986–2012). The total mean annual demand for the same period was 10,461,123 m3 and thus a mean annual unmet demand of 127,682 m3. The highest mean monthly unmet water demand was that of agriculture in the lower part of the catchment in January (90,200 m3). Management practices that would enhance the sustainable management of water resources include construction of a reservoir and enforcement of minimum environmental flows maintenance in the river and these are recommended for the Arror watershed.

URBAN STREAM RESTORATION AND APPLIED PRACTICES IN NORTHEAST ILLINOIS

INTRODUCTION: In-stream and watershed dynamics in urban and urbanizing areas have significant impacts on local property and infrastructure, as well as the quality of the stream itself including: water quality, habitat, physical characteristics, and biodiversity. As land development occurs, natural vegetation and exposed soils are converted to buildings, pavement and other impervious surfaces. This leads to increased runoff during storm events as well as decreasing the time that it takes that stormwater to reach streams, wetlands, and other stormwater storage and conveyance systems. These hydrologic changes in a watershed often occur at a rapid pace which results in rapid destabilization and degradation of streams and rivers. Rivers and streams are naturally dynamic systems. They naturally erode and reshape themselves based on changes to the watershed or the stream itself. Erosion and deposition are natural processes that have always been important components of stream systems and in and of themselves are not undesirable. When natural stream dynamics are rapidly accelerated, however, an entire series of negative impacts to the stream and the biological systems that are depended on the stream occur. Rapid destabilization of streams often leads to significant bank and bed erosion that negatively impact stream health and frequently leads to negative impact to property, buildings and structures, as well as public infrastructure. Past approaches to stream bank and bed stabilization often involved channelization, armoring, and other gray infrastructure techniques to protect public and private property in the effected reaches of streams and rivers without taking into account the overall stream system dynamics. Early stabilization efforts frequently led to other unintended consequences by accelerating the rate of bank and bed erosion in untreated reaches, inadvertent flooding, and other infrastructure impacts. The complex nature of stream dynamics and fluvial geomorphology when applied to urban stream systems and significantly modified watersheds require the need for detailed analysis of the morphology of the stream. Consideration of the complex factors and processes that make up fluvial morphology are critical when selecting practices or methods of stream restoration. Many agencies and cooperative partners work to accumulate and analyze case studies and detailed research in order to develop a method of evaluating and prescribing different stream restoration techniques based on the morphologic conditions in the stream reach (Lyn D.A., and Newton J.F., 2015). An accumulation of case studies, research, and scholarly work on stream restoration techniques and practices helps shape and inform designers across multiple agencies in order to effectively select and design restoration practices. Ultimately, in urban streams, the designer is working to establish a condition of dynamic equilibrium in the treated stream reach. Dynamic equilibrium is defined as a stream reach that is in balance with sediment transport, aggradation, degradation, and bank and bed erosion. When those characteristics are in balance based on the inputs of sediment within the watershed, the bed load and sediments the stream transports, and discharge rate and volume, then the stream is considered to be in a relatively stable state (FISRWG, 1998). The selection then of stream restoration and stabilization practices in urban areas is dependent on not only the reach being treated, but also on the overall watershed dynamics. In addition to the physics of the actual practices implemented, including resistance to shear stresses and velocity of the water flow within the stream channel being treated, the practices must also take into account the larger picture of stream dynamics including sediment delivery and transport, within the watershed and not just within the treated reach. Successful urban stream restoration and stabilization techniques mimic the structures found in more undisturbed systems through the utilization of similar materials in an engineered configuration. In many streams the use of a combination of hard and soft armorment and stabilization solutions including stone, woody debris materials, modern geosynthetic reinforcement devices and native vegetation to stabilize and naturalize stream channels, thereby provided enhanced habitat, better water quality, and protecting property and infrastructure.