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In this study, a method was developed for the baseline characterization of river bathymetry and time-varying heights using globally available datasets from the Shuttle Radar Topography Miss...

The Mekong River Basin (MRB) is undergoing rapid dam development, which is altering the river suspended sediment concentration (SSC). In this study, we used satellite remote sensing records...

This study explored the operational feasibility of an empirical approach to flood inundation forecasting using quantitative precipitation forecasting (QPF) from high-resolution numerical we...

In this study, a numerical modeling framework for simulating extreme storm events was established using the Weather Research and Forecasting (WRF) model. Such a framework is necessary for t...

The design of the dams usually considers available historical data for analysis of the flood frequency. The limitation of this approach is the potential shift in flood frequency due to physically plausible factors that cannot be foreseen during design. For example, future flood extremes may change, among other factors, due to strong local atmospheric feedbacks from the reservoir and surrounding land use and land cover (LULC). Probable maximum flood (PMF), which is the key design parameter for hydraulic features of a dam, is estimated from probable maximum precipitation (PMP) and the hydrology of the watershed. Given the nonlinearity of the rainfall-runoff process, a key question that needs to be answered is How do reservoir size and/or LULC modify extreme flood patterns, specifically probable maximum flood via climatic modification of PMP? Using the American River Watershed (ARW) as a representative example of an impounded watershed with a large artificial reservoir (i.e., Folsom Dam), this study ...

The ongoing drought in California seems to indicate that water managers are now paying greater attention to the use of numerical models of the atmosphere for short-term (7–10 days) weather forecasts. At the time of writing this article, a bill to Congress was being formulated that essentially aims to make the rule curves for large dams more adaptive through the use of numerical models for weather forecast. The use of such models is expected to reduce wastage of impounded water for dam managers and allow more flexibility in water storage and release during periods of anomalous/ off-season big droughts or floods. The purpose of this opinion article is to shed light on the current state of hydropower generation in the United States and discuss how the use of such numerical models of the atmosphere can also maximize energy production while conserving water or protecting against floods. As a clean and renewable energy source, hydropower has been extensively exploited by human beings for over 100 years. According to the 2014 Hydropower Market Report released by the Department of Energy (DOE), there are 2,198 active hydropower plants with a total operational capacity of 79.64 gigawatts (GW) in the United States. Hydropower accounts approximately 7% of the total power generated in the United States (Uria-Martinez et al. 2015). Unfortunately, hydropower generation capacity has stagnated the last two decades since the 1990s owing to lower economic growth (Hall et al. 2003), stricter environmental regulations, a stagnant energy market, and recent breakthroughs in the shale gas and oil industries (such as fracking). Nevertheless, hydropower remains the single largest source of renewable energy because of its relatively low-cost and sustainable characteristics. Compared to other renewable energy sources, hydropower has several unique advantages (USBR 2005). For example, a dam, which is normally considered an expensive investment to build, has a long service life spanning at least 50–100 years. Hydropower remains a more stable and durable source compared to wind or solar power, which are vulnerable to changing or unpredictable weather conditions. Hydropower production is relatively easier to ramp up or scale back depending on the transient nature of power demand. There are also no greenhouse gas emissions as byproducts during hydropower generation. A few U.S. states that are gifted with abundant water resources and topography have already harnessed hydropower as a clean and reliable electricity generation source, such as Washington, Oregon, and California (Fig. 1). Collectively, these three states have the largest installed hydropower capacity, which is equivalent to half of the total installed capacity across the United States. Among these three states, Washington has the largest share with approximately 30.4% of total hydropower generation in the United States, which also amounts to 70% of total electricity generation in the state of Washington. Oregon and California contribute 13.5% and 6.3%, respectively to the national grid in hydropower sector. Compared to the Northwest’s large amount of installed capacity, the Northeast has the most hydropower facilities, which typically are aged and small-capacity. The states that rely more on locally available hydropower apparently have lower electricity price compared to other states that have limited access to hydropower generating resources (UriaMartinez et al. 2015). Because building a new power plant is expensive, the low prices are usually in the states that have extensive power facilities where owners have already paid off the capital cost. The three northwestern states (Washington, Oregon, Idaho) are clear examples of cheap electricity pricing due to abundant hydropower resources.

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

This case study presents a risk analysis reassessment for the oldest dam in the Tennessee River basin—the Wilson Dam—based on postdam flow data. The hydrologic risk of old Wilson Dam was computed from historical flow data (spanning pre and postdam periods) and reservoir volume at the dam site. Additional flow data not previously used in the design phase of the dam helped to update more robustly the probability of flood occurrence that exceeded a particular return period during the life of a dam. The generalized extreme value (GEV) distribution was fitted to historical peak flow (at the dam site) and annual maximum reservoir volume using the L -moment method. This reassessment approach has wide application in reservoir water and safety management for aging dams. The study underscores the need for a review of risk analysis for aging dams that have extensive postdam flow data, particularly in the United States. Furthermore, this case study also demonstrates the unique value of the L -moment method in incorpo...

Unanticipated 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...

Retired, Subcommittee on Water Resources and Environment, Committee on Transportation and Infrastructure, B-375 Rayburn House Office Building, Washington, DC 20515. Forum papers are thought-provoking opinion pieces or essays founded in fact, sometimes containing speculation, on a civil engineering topic of general interest and relevance to the readership of the journal. The views expressed in this Forum article do not necessarily reflect the views of ASCE or the Editorial Board of the journal.

This study presents the development of a probabilistic discharge prediction scheme based on an uncertainty framework called generalized likelihood uncertainty estimation ~GLUE!. By being explicit about a hydrologic model's parameter uncertainty, historical data is used adaptively on a storm-to-storm basis to derive ensembles of representative parameter sets, along with the corresponding likelihood weights of discharge prediction quantiles. The quantile with highest likelihood weight represents the most probable discharge hydrograph, with upper/lower uncertainty limits represented by the various upper/lower likelihood weight quantiles. On the basis of new data, the Bayesian theorem is used to update for the posterior representative parameter sets and likelihood weights of prediction quantiles. The probabilistic scheme is evaluated using 15 flood-inducing storms over a medium-sized watershed in northern Italy. The scheme's dis- charge predictions on the basis of its highest likelihood quantile are evaluated comparatively to the conventional single optimum parameter set prediction. It is observed that the two methods have comparable accuracy in terms of the overall hydrograph prediction, but the probabilistic scheme is subject to 50% less variability in time to peak error. The probabilistic scheme has an added value important to decision making and risk assessment, which is its ability to provide consistent assessment of uncertainty in such major flood parameters as peak runoff and time-to-peak. The procedure is simple in design, model-independent, and can be easily implemented in real-time for computationally efficient rainfall-runoff models. DOI: 10.1061/~ASCE!1084-0699~2005!10:2~141! CE Database subject headings: Floods; Predictions; Uncertainty analysis; Probabilistic methods; Decision making .

Modern dams are overwhelmingly designed under the assumption of climatic stationarity by using a static design value known as probable maximum precipitation (PMP). Therefore, it is worthwhile to explore the impact of relaxing the assumption of stationarity and recalculating design PMP values by using currently practiced procedures enhanced by numerical modeling or observational climate trends. This study reports the findings of nonstationary PMP recalculations at three large dam sites in the United States (South Holston Dam in Tennessee, Folsom Dam in California, and Owyhee Dam in Oregon). The results indicate that currently accepted PMP values are significantly increased when future changes in dew points from observational trends or numerical models are taken into account. It is plausible that such future changes in these meteorological thresholds, had they been known among the engineering community when PMPs were designed, would have received the necessary attention regarding the future uncertai...

Almost all observational studies report that extreme precipitation in the U.S. has increased in magnitude over the last several decades (Groisman et al. 1999, 2013; Kunkel et al. 2013). Although such studies differ regarding the geographic influence of trends, the consensus on extreme precipitation (i.e., short-term events with a 5% exceedance probability or less) is surprisingly unequivocal. The American Meteorological Society (AMS) 2013 State of Knowledge report on extreme precipitation (Kunkel et al. 2013) states that “There is strong evidence for a nationally averaged upward trend in the frequency and intensity of extreme precipitation events : : : ” and that the in situ measurement network is considered “adequate to detect such trends.” In a slightly more recent study, Groisman et al. (2013) reported that the very heavy precipitation rates (in the upper 5% of all records) have increased over approximately two-thirds of the eastern U.S. during the last 30 years, whereas the number of days with maximum daily convective available potential energy (CAPE) values exceeding 1,500 J=kg has increased ∼30% in the same period during the spring season. Although the potential causes of this increasing trend may be multifactorial, the most recent AMS report also indicates increasing atmospheric water vapor as a leading causative factor (Kunkel et al. 2013). Despite the overwhelming consensus on the rising trend of extreme precipitation rates, the response of peak stream flow is not as unequivocal. Although regulation of surface flow, increasing imperviousness, and altering infiltration rates through land cover change are some of the many ways peak flow distribution can be impacted during a stationary precipitation regime, a clear signal of the rising trend of extreme precipitation may be expected in peak flow records. However, the paradox of peak flow is that any rising trend in peak flows is much more elusive to observe over statistically significant locations. Vogel et al. (2011) analyzed as many as 14,000 U.S. streamflow records and found statistically significant increases in flood risk at only approximately 10% of the stations. They also attributed most of this increase to hydrologic changes in land cover (increasing imperviousness, and hence, increased surface runoff generation) rather than global warming. Villarini et al. (2009) analyzed 50 stream flow stations with more than a centurylong record of flow observations using sophisticated methods for change point detection, trend analysis, and nonstationarity. However, they concluded that “it is easier to proclaim the demise of stationarity of flood peaks than to prove it through analyses of annual flood peak data.” Hydrologic extremes are the foundation of most design, operation, and risk management of water management systems that currently serve society. Yet, the current hydrology that traditionally models only the natural laws of physics of a watershed has become increasingly limited in its ability to provide relevant answers for emerging changes that are observed (Vogel 2011). This is because traditional hydrology continues to assume that the extensive replumbing of the natural water network, along with changes to land cover and hemispheric forcing of climate change attributable to extensive human activity, are only an external forcing rather than an integral part of the coupled human–natural system. The massive but gradual redistribution of water through artificial reservoirs, numerous irrigation schemes, land cover change, and urbanization since the early 1900s has resulted in a nonnegligible contribution to increased moisture availability and altered atmospheric convergence patterns overland in the U.S. (Puma and Cook 2010; DeAngelis et al. 2010). For example, USGS records (Kenny et al. 2009) indicate an increase in irrigation acreage from 141; 000 km (in 1950) to 263; 000 km (in 2005). The latter is equivalent to a withdrawal of 144 million acre-ft (or 177 km) of surface and ground water per year that evaporates directly to the atmosphere [and may be recycled as precipitation (Eltahir and Bras 1996)], and likely balances any increases in peak flow attributable to rising precipitation rates. Similarly, approximately 75,000 artificial reservoirs were built in the U.S. during the last century, with a total capacity almost equaling one year of mean runoff (Graf 1999, 2006; Global Water Systems Project 2008). The cumulative effect of these extensive impoundments has been to triple the average residence time of surface water from 0.1 years (in 1900) to 0.3 years in 2000 (Vorosmarty and Sahagian 2000), an aspect that clearly has not received attention during the assessment of peak flow trends. Similar large-scale alterations have happened to the natural land cover in the U.S., which have modified both hydrologic behavior (water partitioning) and radiative behavior (energy partitioning) in nonnegligible amounts (Pielke et al. 2011). The explicit consideration of the human replumbing of natural water systems may only explain part of the peak flow paradox. For example, global warming may intensify evaporative fluxes and initiate regional drying of soils. This would compensate for increasing precipitation rates through increased abstraction of precipitation and potentially lowering of peak flows. Thus, the hydrologic engineering community may need to employ a multifactorial approach involving, as a fundamental premise, the human impact (feedback) on local-to-regional weather and climate that have been researched for over many decades (Pielke 2009; Mahmood et al. 2010), but overlooked in most studies of hydrologic extremes (Hossain et al. 2012). Understanding the causative factors behind the historical evolution of extreme precipitation and peak flow is probably the most urgent priority for current hydrologists to adapt the design and operation of infrastructure. Through an investigation of the combined role of this land–atmosphere feedback owing to artificial redistribution of water, land cover change and climate change, one may postulate that the paradox of peak flows not having responded in sync with rising extreme precipitation may be better understood. Consequently, this approach may allow the hydrologic engineering community to understand how peak flow patterns, which are used in the frequency analysis and design of