Wondmagegn Yigzaw

Climate feedback-based provisions for dam design, operations, and water management in the 21st century

As the world’s population increases, the rising demand for water will be compounded further by the need to sustain economic growth (Vorosmarty et al. 2000). According to one report by the United Nations Environment Program (UNEP), the stress on freshwater resources is expected to significantly magnify and spread to other regions of the world by 2025 (see Fig. 1; UNEP 2002). Historically, one of the common engineering solutions to guarantee a steady water supply against a rising demand has been to construct surface water impoundments on rivers. Such large-scale infrastructure, commonly known as dams and artificial reservoirs, trap a sufficiently large amount of water from the local hydrologic cycle to make up for a shortfall when demand exceeds the variable supply from nature. In other words, dams can be regarded as a strategic (long-term) solution to resolve the tactical (short-term) challenges of balancing the water deficit compounded by population growth and economic activity. In the United States, statistics suggest that building dams is outdated and considered a twentieth-century construct by the civil engineering profession (Fig. 2) Graf et al. 2010; Graf 1999). However, for vast regions of the underdeveloped or developing world, large dam-construction projects are being implemented in increasing numbers for tackling the rising water deficit in emerging economies (Fig. 3). Examples of such large dam projects are the Southeast Anatolia Project, or GAP (Turkish acronym) project, in Turkey, comprising 22 dams on the Tigris and Euphrates rivers (Unver 1997), the Three Gorges Dam (TGD) in China (Shen and Xie 2004), Itaipu Dam in Brazil (Pierce 1995), and the proposed Indian River Linking Project (Misra et al. 2007). From a global perspective, dam operations and water management in impounded basins remain relevant worldwide, while dam design and building are pertinent mostly to the developing world, comprising Africa, South America, and Asia, where most of the rivers remain unregulated. The heritage of modern dam building is nearly a century old. For example, the construction of the oldest dam in the Tennessee River Valley, called the Wilson Dam in Alabama, began in 1918 (Gebregiorgis and Hossain 2012). With a long heritage built on knowledge gained from previous failures and success stories, the civil engineering profession has made tremendous progress in dam safety against hazards of earthquakes (e.g., Marcuson et al. 1996), piping/seepage (e.g., Casagrande 1961; Sherard 1987), structural instability (e.g., Terzaghi and LaCroix 1964; Vick and Bromwell 1989), and optimization of dam operations to serve multiple, but competing, applications (Dai and Labadie 2001; Datta and Burges 1984). Similarly, much is now known about the management of postdam effects on aquatic ecology (e.g., Ligon et al. 1995; Richter et al. 1996), riparian vegetation (e.g., Merritt and Cooper 2000), geomorphology (e.g., Graf 2006), and dam removal as a result of sedimentation (Morris and Fan 1998; Graf et al. 2010). In general, the aspects of dam design and operations that have improved during the last century are those that are directly visible or have instantaneous impact on the land surface. This is not surprising, as the essence of engineering is hands-on in nature. What can be touched, sensed, and immediately visualized in the real world can be accounted for in the design and operation of an infrastructure. For example, the importance of fish ladders to minimize the disturbance to predam fish-migration paths was quickly appreciated by the engineering community during the early history of dam building. Now fish ladders are a common provision during the planning of a dam along a river. Similarly, when the Teton Dam failed (Sherard 1987), the importance of design provisions to minimize seepage, particularly in karstic geology, has now become a standard engineering practice. The Wolf Creek Dam, the largest artificial reservoir east of the Mississippi River, has periodically undergone grouting of seepage holes throughout its existence (Boynton and Hossain 2010). With increased fluctuation of flows downstream of dams, it did not take long for the concept of environmental flow (Tharme 2003) and indicators of hydrologic alteration (IHA) (Richter et al. 1996) to be devised for better ecosystem-centric dam operations in impounded basins. When more residential and commercial development is planned in an impounded river basin, it is intuitive to the engineer that the increase in imperviousness of the land surface may require larger detention basins at select locations to account for the increased runoff and erosion from excess rainfall. The climatic impacts (i.e., feedbacks) of dams, however, are unique areas that have received little consideration by the engineering profession for dam building and operations. Climate, by virtue of its definition, represents anything but a hands-on phenomenon. Unlike weather, climate impacts are not measured instantaneously. Given the current breadth of engineering curricula that exclude atmospheric and climate-science subjects as prerequisites at the freshmen and sophomore levels, a large artificial lake having an

Crossing the “Valley of Death”: Lessons Learned from Implementing an Operational Satellite-Based Flood Forecasting System

More than a decade ago, a National Research Council (NRC) report popularized the term “valley of death” to describe the region where research on weather satellites had struggled to reach maturity for societal applications. A similar analogy can be drawn for other satellite missions, since their vantage point in space can be highly useful for some of the worlds otherwise fundamentally intractable operational problems. One such intractable problem is flood forecasting for downstream nations where the f looding is transboundary. Bangladesh fits in this category by virtue of its small size and location at the sink of the mighty Ganges and Brahmaputra. There has been the claim made that satellites can be a solution for Bangladesh in achieving forecasts with lead times beyond three days. This claim has been backed up by scientific research done by numerous researchers, who have shown proof of concept of using satellite data for extending flood forecasting range. This article aims to take the reader on a journe...

A Promising Radar Altimetry Satellite System for Operational Flood Forecasting in Flood-Prone Bangladesh

Building on a recent suite of work that has demonstrated theoretical feasibility and operational readiness of a satellite altimeter based flood forecasting system, we recently put a progressively designed altimeter based transboundary flood forecasting system to the ultimate test of real-time operational delivery in Bangladesh. The JASON-2 satellite altimeter, which was in orbit at the time of writing this manuscript, was used as the flagship altimeter mission. This paper summarizes the entire process of designing the system, customizing the workflow, and putting the system in place for complete ownership by the Bangladesh stakeholder agency for a 100 day operational skill test spanning the period of June 1 2013 through Sept. 9, 2013. Correlation for most of the flood warning stations ranged between 0.95 to 0.80 during the 1 day to 8 days lead time range. The RMSE of forecast typically ranged between 0.75m to 1.5m at locations where the danger level relative to the river bed was more than an order higher (i.e., >20m). The RMSE of forecast at the 8 days lead time did not exceed 2m for upstream and mid-stream rivers inside Bangladesh. The RMSE of forecast at the 8 days lead time exceeded 2m at a few estuarine river locations affected by tidal effects, where danger level relative to river bed was smaller (i.e., <;20m). Such a satellite altimeter system, such as one based on the JASON-2 altimeter, is now poised to serve the entire inhabitants of the Ganges-Brahmaputra-Meghna river basins as well as 30 or more flood-prone downstream nations currently deprived of real-time flow data from upstream nations.

Comparison of PMP-Driven Probable Maximum Floods with Flood Magnitudes due to Increasingly Urbanized Catchment: The Case of American River Watershed

AbstractSince historical (predam) data are traditionally the sole criterion for dam design, future (postdam) meteorological and hydrological variability due to land-use and land-cover change cannot be considered for assessing design robustness. For example, postdam urbanization within a basin leads to definite and immediate increase in direct runoff and reservoir peak inflow. On the other hand, urbanization can strategically (i.e., gradually) alter the mesoscale circulation patterns leading to more extreme rainfall rates. Thus, there are two key pathways (immediate or strategic) by which the design flood magnitude can be compromised. The main objective of the study is to compare the relative contribution to increase in flood magnitudes through direct effects of land-cover change (urbanization and less infiltration) with gradual climate-based effects of land-cover change (modification in mesoscale storm systems). The comparison is cast in the form of a sensitivity study that looks into the response to the ...

Toward a Methodology to Investigate the Downstream Flood Hazards on the American River due to Changes in Probable Maximum Flood due to Effects of Artificial Reservoir Size and Land-Use/Land-Cover Patterns

AbstractRecent research in mesoscale hydrology suggests that the size of the reservoirs and the land-use/land-cover (LULC) patterns near them impact the extreme weather [e.g., probable maximum flood (PMF)]. A key question was addressed by W. Yigzaw et al.: How do reservoir size and/or LULC modify extreme flood patterns, specifically PMF via modification of probable maximum precipitation (PMP)? Using the American River watershed (ARW) as a representative example of an impounded watershed with Folsom Dam as the flood control structure, they applied the distributed Variable Infiltration Capacity (VIC) model to simulate the PMF from the atmospheric feedbacks simulated for various LULC scenarios. The current study presents a methodology to extend the impacts of these modified extreme flood patterns on the downstream Sacramento County, California. The research question addressed is, what are the relative effects of downstream flood hazards to population on the American River system under various PMF scenarios f...

Land Use and Land Cover Impact on Probable Maximum Flood and Sedimentation for Artificial Reservoirs: Case Study in the Western United States

AbstractUnanticipated peak inflows that can exceed the inflow design flood (IDF) for spillways and result in possible storage loss in reservoirs from increased sedimentation rates lead to a greater risk for downstream floods. Probable maximum precipitation (PMP) and probable maximum flood (PMF) are mostly used to determine IDF. Any possible change of PMP and PMF resulting from future land use and land cover (LULC) change therefore requires a methodical investigation. However, the consequential sediment yield resulting from altered precipitation and flow patterns into the reservoir has not been addressed in literature. Thus, this study aims to determine the combined impact of a modified PMP on PMF and sediment yield for an artificial reservoir. The Owyhee Dam of the Owyhee River watershed (ORW) in Oregon is selected as a case study area for understanding the impact of LULC change on PMF and sedimentation rates. Variable infiltration capacity (VIC) is used for simulating streamflow (PMF) and the revised uni...

Water sustainability of large cities in the United States from the perspectives of population increase, anthropogenic activities, and climate change

Balancing water demand and supply with depleting sources and increasing demand needs a multi-dimensional approach given the pace at which the world is urbanizing. This study selected the contiguous United States (CONUS), 42 specific cities and their river basins to determine: Which basins and cities are more susceptible to increased water shortage? Population, water use, hydrologic model and climate model data from CMIP5 were used. Representative Concentration Pathways scenarios: RCP2.6, RCP4.5, RCP6, and RCP8.5 represented different climate change conditions. Period 1 (1950–2004) showed that more areas are affected by monthly runoff and streamflow than annual averages. In some cases, significant decreasing trends in water availability were observed during the summer (June–July–August) and spring (March–April–May) seasons. The second period (2005–2049) indicated an annual increasing trend (more water available) with higher intensity for the RCP6 scenario. Summer and spring showed areas of decreasing trend (less water available) for RCP4.5 and RCP6. Period 3 (2050–2099) exhibited a decreasing trend for the RCP2.6 (Western and Central CONUS, Great Lakes, and FL), RCP4.5 (Southwest CONUS), RCP6 (Western United States), and Central CONUS (RCP8.5). The Mississippi River has a mixed sensitivity to future climate change. The Central Valley of California, Los Angeles, Phoenix, and Tucson can face further challenges as the Colorado River becomes depleted. Seawater desalination and inter-basin water transfer can be considered in future and present policies and structural developments. The West, Southeastern Coast, and FL may consider desalination, while the West and Central CONUS can use the Mississippi for inter-basin transfer.

Water Resources Vulnerability in the Context of Rapid Urbanization of Dhaka City (a South Asian Megacity)

Megacities of South Asia face the challenges of decreasing recharge and dwindling ground water resources because of rapid urbanization, high population growth, and rural-to-urban migration. Sustainable approaches for water resources in the future should account for such trends and patterns in the context of increasing urbanization, imperviousness, and dwindling recharge. This study explores the water resources vulnerability for one of the fastest growing megacities in Asia, Dhaka (in Bangladesh), using a bottom–up contextual approach. Using observational evidence, it pursues questions such as what are the patterns of rainfall and urban runoff around Dhaka city and how can they be leveraged for sustainable water resources planning ? The study finds that rainfall experiences strong spatial signature, where the region downwind of the city seems to receive statistically higher rainfall than the upwind region. In the wider context of the country, the study also finds that urban regions in general receive less rainfall than nonurban regions. Finally, at the current state of urbanization, approximately 62% of the rainfall is predicted to be available as urban runoff for Dhaka city, which currently is untapped as a potential mitigating source. Projected water demand and population growth indicate that this source of urban runoff could be used for artificial recharge and buildup of groundwater stock by reducing the pressure on groundwater extraction until 2025. An independent pilot-scale study conducted by Bangladesh Institute of Water Modeling on artificial recharge from rain water harvesting has recently verified the effectiveness of the vulnerability assessment approach of the study as a decision-making tool for the adaptation community.