Rollin H. Hotchkiss

Disturbance is known to be a dominant variable in stream ecology. Disturbance can be the result of hydraulic or physical modifications to the environment. Periphyton assemblages are composed of attached algae, bacteria, and fungi growing on the streambed. The assemblages can be viewed as a necessity or a nuisance depending on stream productivity. Periphyton community structure is highly dependent on disturbance regime. The objective of this research was to investigate temporal variations in periphyton resistance to shear stress scour. The research was accomplished by colonizing clay tiles in a natural stream for various time periods. The tiles were periodically collected and subjected to increasing levels of shear stress in a laboratory flume. The tiles were then analyzed to determine the level of periphyton scour. It was found that periphyton ash free dry mass increased significantly with colony age and time of the growth season. Periphyton resistance to scour increased with colony development but was not significantly influenced by time. The results can be used to improve restoration and management of stream systems.

Global climate change will likely modify the availability of surface and ground water. It is necessary to evaluate the potential impacts of climate change on water resources to assist in policy decisions. Water resources impact assessments are often completed with hydrologic models. This draws into question the temporal and spatial scales over which these models are developed and evaluated. The objective of this paper was to evaluate the impacts of climate change on Missouri River Basin water yields at multiple temporal scales. This was accomplished by developing a hydrologic model of the basin. The model was conducted for baseline and changed climate conditions. The climate change data was provided by a Global Circulation Model and downscaled with a Regional Climate Model. Water yield increased significantly under the changed climate simulation for all temporal scales. The insensitivity of results to temporal scale was likely due to the large sample size and the strong effects of climate change on water yield. Future research will expand this work to include assessment of spatial model scales.

Experiments were performed to investigate the energy dissipation realized at the outlet of a culvert using two simple design alternatives: (1) Design I, a simple weir near the culvert outlet, and (2) Design II, a weir with a drop upstream in the culvert outlet barrel. The two designs are intended to reduce the flow energy at the outlet by inducing a hydraulic jump within the culvert barrel, without the aid of tailwater. This paper examines the jump geometry, the effectiveness of each jump type, and proposes a design procedure for practicing engineers. The design procedure is applicable to culverts with approach Froude numbers from 2.6–6.0. Both designs are effective in reducing outlet velocity 0.7 to 8.5 ft/s (0.21–2.59 m/s), momentum 10–48%, and energy 6–71%. The design layouts allow easy access for maintenance activities.

In 2000, the first author presented a report on the ability to simulate a swimming fish using numerical solutions to the equations of motion. This paper is a report of significant progress towards the solution of this complex problem. The propulsion mechanism of a 10 cm rainbow trout (oncorhynchus mykiss) swimming steadily in undulatory mode was investigated. A 2-D laminar unsteady incompressible Navier-Stokes computational model was developed which utilized a moving adaptive mesh (Fluent 6.1). The simulated wake was dominated by a reverse von Karman vortex street previously observed experimentally. Thrust and drag forces acting on the trout were quantified and the equilibrium condition was satisfied within 5%. To better evaluate the models' ability to investigate swimming mechanisms, a logical next step would be a comparison of a wider variety of swimming cases. This could be accomplished by varying the wave speed, the swimming speed, the amplitude function, and several other parameters. Body thickness should be added to the model since it will most likely increase drag and better simulate the equilibrium condition for steady swimming. Adding turbulence and creating a 3-D simulation would provide the most accurate and realistic numerical simulation of a rainbow trout.

Flow over a sharp-crested weir can create dangerous countercurrents downstream under high tailwater conditions. A comprehensive experimental design project in open-channel hydraulics used in a senior/graduate course and in a freshman exploratory experience is illustrated. This applied problem allows the instructor to demonstrate hydraulic jumps, aerated versus nonaerated nappes, similitude and modeling, and the need for experimentation in hydraulics. A series of experiments requires students to compare their predictions of several parameters to those measured, and asks them to design a supplemental structure for the weir to reduce the power of the frontal vortex such that people are ejected and carried downstream to calmer water. The student designs are then tested in the flume during class. During the course of the project, spontaneous discussions occur about the extent to which engineers should be held liable for designs that may increase the likelihood of death. The experiments have been well received ...

Water from the Missouri River Basin is used for multiple purposes. The climatic change of doubling the atmospheric carbon dioxide may produce dramatic water yield changes across the basin. Estimated changes in basin water yield from doubled CO₂ climate were simulated using a Regional Climate Model (RegCM) and a physically based rainfall‐runoff model. RegCM output from a five‐year, equilibrium climate simulation at twice present CO₂ levels was compared to a similar present‐day climate run to extract monthly changes in meteorologic variables needed by the hydrologic model. These changes, simulated on a 50‐km grid, were matched at a commensurate scale to the 310 subbasin in the rainfall‐runoff model climate change impact analysis. The Soil and Water Assessment Tool (SWAT) rainfall‐runoff model was used in this study. The climate changes were applied to the 1965 to 1989 historic period. Overall water yield at the mouth of the Basin decreased by 10 to 20 percent during spring and summer months, but increased during fall and winter. Yields generally decreased in the southern portions of the basin but increased in the northern reaches. Northern subbasin yields increased up to 80 percent: equivalent to 1.3 cm of runoff on an annual basis.

The Great Plains of the United States, drained primanly by the Missouri River, are very sensitive to shifts in climate. The six main stem dams on the Missouri River control more than one‐half of the nearly 1.5 million square kilometer basin and can store three times the annual inflow from upstream. The dams are operated by the U.S. Army Corps of Engineers using a Master Manual that describes system priorities and benefits. The complex operational rules were incorporated into the Soil and Water Assessment Tool computer model (SWAT). SWAT is a distributed parameter rainfall‐runoff model capable of simulating the transpiration suppression effects of CO₂ enrichment. The new reservoir algorithms were calibrated using a 25‐year long historic record of basin climate and discharge records. Results demonstrate that it is possible to incorporate the operation of a highly regulated river system into a complex rainfall‐runoff model. The algorithms were then tested using extreme climate scenarios indicative of a prolonged drought, a short drought, and a ten percent increase in basin‐wide precipitation. It is apparent that the rules for operating the reservoirs will likely require modification if, for example, upper‐basin precipitation were to increase only ten percent under changed climate conditions.