Journal of Hydrologic Engineering

Hydrologists have attempted to relate the hydrologic response of watersheds as runoff production from rainfall to watershed topographic structures for many years. The recently proposed geomorphologic instantaneous unit hydrograph (GIUH) method is perhaps the most promising development in this direction; if successful, it would allow the derivation of the unit hydrograph (UH) for ungauged or inadequately gauged watersheds without the need of observed runoff and rainfall data. In this method, the geomorphic ratios of the Horton-Strahler stream-ordering laws are incorporated in the GIUH model for UH generation. In view of the variety of project requirements and the different levels of topographic detail available from maps or geographic information systems (GISs), five different levels of geomorphic data are allowed for incorporation with a kinematic-wave and stream-law based instantaneous UH model. Testing of the model on two hilly watersheds in the eastern United States and two relatively flat-slope watersheds in Illinois are presented. Comparison between the simulated and observed hydrographs for a number of rainstorms indicate the potential of this model as a useful tool in watershed rainfall-runoff analysis.

Two methods for predicting direct runoff from rainfall data were applied to several basins and the resulting hydrographs compared to measured values. The first method uses a geomorphology-based unit hydrograph to predict direct runoff through its convolution with the excess rainfall hyetograph. The second method shows how the resulting hydraulic routing flow equation from a kinematic wave approximation is solved using a spectral method based on the matrix representation of the spatial derivative with Chebyshev collocation and a fourth-order Runge-Kutta time discretization scheme. The calibrated Green-Ampt (GA) infiltration parameters are obtained by minimizing the sum, over several rainfall events, of absolute differences between the total excess rainfall volume computed from the GA equations and the total direct runoff volume computed from a hydrograph separation technique. The improvement made in predicting direct runoff using a geomorphology-based unit hydrograph with the ephemeral and perennial stream network instead of the strictly perennial stream network is negligible. The hydraulic routing scheme presented here is highly accurate in predicting the magnitude and time of the hydrograph peak although the much faster unit hydrograph method also yields reasonable results.

Two methods of analysis were utilized in the evaluation of over 70 sets of slug test data taken from a contaminated site in southwestern Ohio. The tests were performed in till and a variety of underlying glacial outwash sediments ranging from clay to gravel. During data analysis it was necessary to carefully evaluate the geometry of the test well and local flow conditions for their conformance to the assumptions of the method of analysis. This paper introduces several situations where the well construction and the flow conditions at the site affected the accuracy and interpretation of the collected test data.

Logarithmically based functions were used to translate wind-speed measurements from weather stations to cropped fields. The translations adjusted the wind measurements for both instrument siting height and effects of vegetation height and roughness. The roughness of the original measurement site, of the vegetation for which wind data were desired and of the general region, were considered. The transfer function is necessary for wind measurements over clipped grass in order to directly predict evapotranspiration from agricultural crops using the Penman-Monteith equation. Differences in crop height and roughness between clipped grass and taller agricultural crops can reduce wind speed over the taller crops by as much as 50% in the lower internal boundary layer.

Recently developed integrated circuit technology and new reliable pressure transducers have made it possible to develop a battery-operated system to automatically fill class A evaporation pans from stored water. The system records and stores the average of 12 pan level records during a 1 min time period at the end of each 15 min period for later transmission to a central data storage facility. The measurement sensitivity of the system is 0.02 cm of evaporation over a range of 3.5 cm. A field calibration of the system showed that there was a very good (R²= 0.999) linear relationship between standard hook gage and pressure transducer water level measurements. This system is being used in remote locations because the circuitry draws very little quiescent current. A small solar panel keeps the system's 12 V battery fully charged.

The free surface occurs as one of the boundaries in all unconfined ground-water flow problems. Determination of the free surface has received considerable attention in the literature. For computing free surface, models have been either developed neglecting the vertical velocity or including the effect of vertical velocity. However, it is found that in certain situations, none of these models are able to simulate the steady-state free surface profiles. With this in view, a new model based on the considerations of vertical velocity is proposed to analyze the free surface in case of steady-state radial seepage. It is found that the existing models of computing free surface are the particular cases of the present model. Also, the computed free surface profiles using the present model are found to match well with the observed profiles. Thus, the present model can be used to represent steady-state free surface profiles.