R. P. Hansen | Geology Reports

USGS1988

The effects of two multipurpose reservoirs on the water temperature of the McKenzie River, Oregon

A one dimensional, unsteady-state temperature model using the equilibrium temperature approach (with air temperature used to estimate equilibrium temperature) is used to evaluate the effects of two Army Corps of Engineers dams and resulting reservoirs on the McKenzie River, from Delta Park (River Kilometer 99.9) to Leaburg Dam (River Kilometer 62.4). Both Corps of Engineers projects are on tributaries to the McKenzie River and at present have only bottom withdrawal capabilities. An effective top width parameter (ETW) was introduced into model calibrations to account for the high turbulence of the reach. Extensive data were collected from May to October, 1983 and 1984. Using these data, water temperatures were predicted to within 0.30 C mean absolute deviation (MAD) at Finn Rock (at River Kilometer 87.2, 4.5 km below the second tributary confluence) and near Vida (River Kilometer 76.8), and to within 0.40 C at Leaburg Dam (River Kilometer 62.4). Since these data represent hydrologic and meteorologic conditions over a very short period, analyses were extended to include three additional historic years and an average conditions year. The average conditions values were obtained by using the mean daily values for the period of record at key stations. Accuracy was lost when simulating historic years, since the only meteorological data available were collected outside the basin, and hence were less representative. Simulation of historic data showed that Corps of Engineers projects have little or no effect on water temperatures of the McKenzie River near Vida (River Kilometer 76.8) from the end of November to the end of May. Projects have a cooling effect from the beginning of June to the first part of September and a warming effect from the middle of September to the end of November. Warming and cooling effects average just over 1 C. There is little or no temperature effect during periods of flood control operation or reservoir filling. Cooling effects are due to conservation holding, when releases are cooler than inflows. Drafting of reservoirs in preparation for flood control causes a warming effect when heat stored in the upper water layers during conservation holding is released as reservoir water levels are lowered. (Author 's abstract)

Water-Resources Investigations Report↗

USGS1988

Simulation of three lahars in the Mount St Helens area, Washington using a one-dimensional, unsteady-state streamflow model

A one-dimensional, unsteady-state, open-channel model was used to analytically reproduce three lahar events. Factors contributing to the success of the modeling were: (1) the lahars were confined to a channel, (2) channel roughness was defined by field information, and (3) the volume of the flow remained relatively unchanged for the duration of the peak. Manning 's 'n ' values used in computing conveyance in the model were subject to the changing rheology of the debris flow and were calculated from field cross-section information (velocities used in these calculations were derived from super-elevation or run-up formulas). For the events modeled in this exercise, Manning 's 'n ' calculations ranged from 0.020 to 0.099. In all lahar simulations, the rheology of the flow changed in a downstream direction during the course of the event. Chen's 'U ', the mudflow consistency index, changed approximately an order of magnitude for each event. The ' u ' values ranged from 5-2,260 kg/m for three events modeled. The empirical approach adopted in this paper is useful as a tool to help predict debris-flow behavior, but does not lead to understanding the physical processes of debris flows.

Washington↗