Browsing by Author "Simons, Daryl B., advisor"

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Open Access
Known discharge uncoupled sediment routing
(Colorado State University. Libraries, 1982) Brown, Glenn O. (Glenn Owen), author; Simons, Daryl B., advisor; Li, Ruh-Ming, advisor; Doehring, Donald O., committee member
A known discharge, uncoupled, sediment routing model, KUWASER has been developed. The model sequentially solves the steady flow and sediment continuity equations. This procedure allows for efficient solution of sediment routing problems on large river systems. The model can perform backwater calculations and sediment routing in main stem and multiple tributaries including divided flow reaches. The user can determine river response to river management practices such as channel improvement, realignment, dredging or tributary modifications. The model was tested against two other models, a stage-discharge relationship and a fixed bed model by comparing the frequency of model errors in stage prediction. A sensitivity analysis was performed to determine the sensitivity of the models results to variations in six input parameters. The Yazoo River Basin in Mississippi was used as a case study to demonstrate the model capabilities. The model can be an effective tool in the prediction of river response.
Open Access
Laboratory study of alluvial river morphology
(Colorado State University. Libraries, 1971-03) Khan, A. K. M. Hamidur Rahman, author; Simons, Daryl B., advisor; Schumm, Stanley, advisor; Richardson, E. V., committee member; Gessler, J., committee member
A concrete recirculating flume 100 feet long, 24 feet wide, and about 3 feet deep was used to study the different alluvial river channel patterns. The flume was filled with sand and a series of tests were made in which discharge was varied from 0.1 to 0.3 cfs and slope was varied from 0.001 to 0.020. Four channel patterns, straight, meandering thalweg, meandering, and braided were observed in the laboratory. Straight channels developed at very flat slopes (slopes flatter than 0.0047 or 0.0026 depending on whether the flow entered the channel straight or at an angle to the axis of the flume) with very low bedload concentrations (less than 740 ppm). Meandering thalweg channels developed for slopes between 0.0023 and 0.013 and for bedload concentrations of 740 and 2180 ppm. The sinuosity was very low in these channels. Braided channels occurred at very steep slopes (slopes equal to or greater than 0.016) with high concentrations of bedload (equal to or greater than 3110 ppm). No meandering channel developed in noncohesive material. Meandering channel developed with 3% concentration of clay in the flow. Velocities were very low in straight channels (less than 0.84 fps). Meandering thalweg channels developed for velocities between 0.84 and 1.53 fps, and braided channels developed for velocities higher than 1.53 fps. Because of such variation of velocity with channel pattern, Froude number of flow, shear, and stream power was very high in a braided channel, very low in a straight channel, and intermediate in a meandering thalweg channel. Because of its low velocity, the flow in a straight channel was incapable of causing any significant erosion and as a result it maintained its original straight alignment. Meandering thalweg and braided channels developed only when the flow conditions were such that there were pronounced erosion of the channel banks. For any given bed material, thalweg meander geometry and channel geometry depend on discharge and slope or discharge and bedload concentration. Thalweg sinuosity in a meandering channel depends on discharge, slope, and bedload concentration. Width-depth ratio of channels was found to increase with bedload concentration. Laboratory experiments showed that a change in the sediment type from bedload to suspended load transforms a wide, shallow, less sinuous meandering thalweg channel into a narrow, deep, and more sinuous meandering channel. The smoothness of bed and banks, caused by the deposition of clay among the coarser materials, reduced the resistance to flow and increased the average velocity. The increased velocity caused scour of the bed. Some of the clay also deposited on the alternate bars. Continued building up of bars and scour of bed along the thalweg caused exposure of bars above water surface and the flow took place in a narrow, deep, and sinuous meandering channel.
Open Access
Mathematical modeling of response from small watershed
(Colorado State University. Libraries, 1974) Li, Ruh-Ming, author; Simons, Daryl B., advisor; Karaki, Susumu, committee member; Labadie, John W., committee member; Meiman, James R. (James Richard), committee member; Shen, H. W., committee member
The physical quantities which describe the major watershed response to the precipitation are the water yield, the sediment yield, and the resultant stream morphology. This study provides the theoretical background and numerical methods for modeling physical processes governing the watershed response. A method of nonlinear kinematic wave approximation for flow routing has been developed to route water and sediment over land and in channels. The numerical scheme developed in this study is unconditionally stable and may be used with a wide range of time increment to space increment ratio without loss of significant accuracy. From theoretical considerations, it has been found that the flow discharge is the better selection for the unknown in numerical computations than the depth or area. The applicability of the numerical method has been tested in various cases - overland flow, natural channel, and small drainage system and has been found satisfactory for modeling of watershed response. As the applications of this flow routing procedure, a rainfall-runoff model for simulating hydrographs from small watersheds and a rainfall erosion model for calculating time-dependent erosion rates from overland flow areas have been developed. The rainfall-runoff model simulates hydrographs on the single storm basis. The model includes the water balance simulation for land surface hydrologic cycle and the water routing features for both overland flow and channel systems. Unlike the conventional approach to parametric modeling of watershed response, this model contains much more information on the physics of flow and requires much less assistance from optimization schemes than any existing water models known to the writer. For the tested basin the simulated hydrographs agree reasonably well with the measured hydrographs. The sensitivity analysis indicates that soil data are very sensitive to the computed hydrograph. Flow resistance parameters and vegetation data are less sensitive to the simulated results. In addition, this physically oriented model has the capability to predict watershed treatment effects on water yields. The rainfall-erosion model simulates both water flow and sediment flow routing in overland flow areas and produces time-dependent erosion rates comparable with the available experimental data from a soil plot. The model can generate time-dependent land forms, and the generated land form tends to be concave in shape which frequently appears in nature. It was also found that the soil erosion rate was very sensitive to the bed slope and shape. The general practice of assuming a uniform shape may result in serious errors. The mathematical models in this study may provide the short-term and the long-term responses. Theoretical interpretation of the long-term response was also made. The equations describing the basic physical processes in small watershed channels sculptured in noncohesive alluvial materials have been employed to derive the hydraulic geometry equations. Both downstream and at-a-station relations were developed. This work provides information on stream morphology response to the modified amount of precipitation or to watershed treatment effects.
Open Access
Scour at culvert outlets
(Colorado State University. Libraries, 1967) Opie, Thomas Roy, author; Simons, Daryl B., advisor; Remmenga, E. E., committee member
The procedures used in, and results of, experiments to determine the size and geometry of scour holes in flat, loose rock beds at culvert outlets are given. A review of four recent approaches to the problem is also included. From a dimensional analysis, the depth of scour at such an outlet is related to the discharge and bed characteristics. The depth of scour has then been related to the length, width and volume of scour. The relations are severely restricted in their application to the range of outlet conditions. Practical examples of data use are given. Results are presented in graphic form.