Search

In view of the rapid proliferation of water infrastructures worldwide, balancing human and ecosystem needs for water resources is a critical environmental challenge of global significance. While there is abundant literature on the environmental impacts of individual water infrastructures, little attention has been paid to their cumulative effects in river networks, which may have basin‐to‐global impacts on freshwater ecology. Here we developed a methodological framework based on Pareto frontier analysis for optimizing trade‐offs between water withdrawal and ecological indicators. We applied this framework to a mountainous Ecuadorian headwater river network that is part of a continental water transfer for supply and demand management to optimize ecological conditions and the operation of 11 water intake structures used to provide potable water to the city of Quito. We found that the current water intake configuration has an important effect on the total length of fifth‐order stream sections (65% reduction compared to premanaged condition) and isolates 70.9% of the headwater stream length. The Pareto frontier analysis identified water intake portfolios (i.e., different combinations of intake sites) that decreased ecological impacts by 7.8% points (pp) and 13.0 pp for connectivity and stream order change, respectively, while meeting Quito's water demands. Additional portfolios accounting for monthly variability in water demand and resources further decrease the ecological impact up to 9.6 pp in connectivity and 13.4 pp in stream order. These eco‐friendly portfolios suggest that adaptive management at basin level may help optimize water withdrawal to fulfill urban demands while preserving ecological integrity. Key Points: We develop a methodological framework to perform trade‐off analyses between water withdrawal and ecological impacts at the basin scaleThrough a Pareto frontier analysis, the operation of 11 water intake structures used to provide potable water to Quito City is optimizedApplication of new water management practices are necessary to reach a more dynamic operation strategy to balance human and ecological needs [ABSTRACT FROM AUTHOR]

Outlet point positions taken from hydrometric stations commonly do not coincide with stream locations extracted from digital elevation models (DEMs). This is a serious problem for accurate watershed delineation of data sets containing numerous outlets, which is critical in regional-scale studies that relate catchment characteristics to basin responses. The advanced outlet repositioning approach (AORA), presented here, replicates the processes involved in manual outlet placement while reducing inefficiency and potential for blunders. The technique uses water body names to identify locations for outlet repositioning that are consistent with nearby outlets. The AORA performance was compared against two existing automated techniques using 993 stations in seven basins in northwest England. The AORA had the fewest repositioning errors in each basin and nearly halved the overall number of errors in the data set, compared with the second-best method. This work highlights the potential errors that may be present in studies that have employed existing automated watershed mapping methods. [ABSTRACT FROM AUTHOR]

A probabilistic model for material transport in a stream network is developed based on geomorphology of the subcatchment and water transit time distribution. A tracer may be a point source or a source distributed over the entire catchment. The tracer particles are transported by advection through streams of different order and also diffuse and react chemically with the sediments lying at the bottom of the streams. Stochastic analysis of travel time is complicated by microscopic exchange processes, which act to retain the tracer in the surrounding medium. These include kinetically controlled exchange with the storage zones, diffusion into the bed sediment, and linear equilibrium sorption. In addition, degradation delays the downstream tracer movement. The sensitivity analysis indicates that for 50% mass arrival the mean arrival time is increased by 3 times for a change in mass transfer parameter, χ*, by 10 times. This increase is further pronounced for higher mass arrivals and higher χ*. The results on a specific application example show that a mere doubling of the uncertain value of diffusive mass transfer rate in the bed sediment reduces the probability that 25% of solute mass arrives at the outlet by ≈90%. The high sensitivity of the probability of the solute mass arrival at the outlet to the uncertain diffusive mass transfer rate implies uncertainty also in predictions of the solute transport process. Thus it can be concluded that the correct estimation of mass transfer rate in the bed sediments within a catchment plays an important role in field-scale estimation of transport parameters. [ABSTRACT FROM AUTHOR]