Journal of Hydrologic Engineering

We describe a system for forecasting flood risk in the 370 km², largely urban Kifissos Basin, Athens, Greece, located in moderate to steep terrain (∼3 h hydrologic response time). A 42 h flood forecast lead time is achieved through the use of an integrated hydro-meteorological system. Rainfall is forecast, on a 6 km grid, with a chain of nested numerical weather prediction models, consisting of a limited area model initialized with results of a global circulation model. Flood risk is assessed by driving a hydrologic model with the forecasted rainfall. The system’s forecast skill is evaluated for two recent, medium-size storm events. Results are encouraging for this initial operational stage, however, they also indicate that integrated hydro-meterological models are not yet mature tools. The weaker part of flood risk assessment is the rainfall forecast, which underestimated cumulative depths and maximum intensities and overestimated duration.

A solution is obtained for flow depleted from a stream when water is pumped from an adjacent well in a semiconfined aquifer. The streambed partially penetrates the aquitard, which forms the top boundary of the pumped aquifer, and the distance between the well and stream is assumed large enough to allow the stream to be modeled with a zero width. The governing partial differential equations for this problem are shown to be equivalent to the equation postulated and solved by Boulton for flow to a well in a delayed-yield aquifer. Consequently, drawdown curves and plots of stream depletion versus time are all found to have two inflection points. However, unlike the solution behavior for Boulton’s problem, aquifer recharge furnished by the stream causes all drawdown and stream depletion curves to approach horizontal asymptotes as time becomes infinite. The solution calculated herein is general enough to reduce to a solution calculated earlier by Hunt when the aquitard becomes impermeable.

A computationally simple method for the estimation of aquifer hydraulic diffusivity from observed piezometric-head variation because of an arbitrary variation in stream stage is proposed. The method makes use of the Fourier series representation of the arbitrary stream-stage variation. The piezometric-head variation due to a sinusoidal change in stream stage is derived in a computationally simple form, which was used as a basic solution in the method. Application of the method on a published data set shows that it accurately estimates the aquifer hydraulic diffusivity with less computational effort and can take into account any variation in stream stage.

This paper presents the results of numerical simulations of groundwater circulation and solute transport at the Salar de Atacama through use of a numerical model to solve the two-dimensional problem of flow in an aquifer when considering the effects of variable density. The phenomena associated with solute transport are modeled by means of an advection–dispersion equation, and a linear relationship is assumed between fluid density and concentration of the dissolved solids. Simulations considered conditions of high groundwater evaporation, which depends on the depth of the phreatic surface. Results indicate that the discharge of groundwater occurs essentially in freshwater–saline water interface zones, where a number of lagunas begin. Different freshwater recharge scenarios were simulated, while it was verified that the effects of evaporation are important and minimize or buffer the variations in the phreatic surface and the discharges of groundwater that are the source of water supply for the lagunas.

A scenic and mountainous area of ancient tropical rainforest in the Caribbean Island of Trinidad has considerable potential for eco-tourism. However, it does not have significant groundwater resources, and its ecologically sensitive nature precludes the construction of impoundment reservoirs. Therefore, the sustainable yield, i.e., 7-day 20-year low flow (7Q20) minus instream flow, of its rivers is one of the critical factors affecting the area’s carrying capacity for eco-tourism. Unfortunately, hydrologic data for the watersheds in this area are either unavailable or insufficient for independently estimating the aforementioned sustainable yield by the conventional methods. Therefore, a hydrologic similarity method was used to obtain 7Q20 of the ungauged rivers. Further, the instream flow was estimated, in the absence of any local criterion, by instream flow incremental methodology. This paper describes the application of these two methodologies and presents the results, which indicated that owing to the presence of a hydraulic threshold for the commencement of habitat stress, the sustainable yield should not exceed 20–30% of 7Q20. It is believed that this technical note would be of interest to practicing hydrologic engineers, whose work may sometimes relate to an area where rainfall and stream flow data are sparse, discontinuous, and nonconcurrent, and the criteria for instream flow are not yet developed.