Please use this identifier to cite or link to this item: https://hdl.handle.net/11681/13439
Title: Kahoma Stream channel improvement project, Maui, Hawaii : hydraulic model investigation
Authors: United States. Army. Corps of Engineers. Pacific Ocean Division
George, John F.
Keywords: Channels
Hydraulic engineering
Hydraulic models
Channel improvement
Kahoma stream
Maui
Hawaii
Streams
Rivers
Publisher: Hydraulics Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Series/Report no.: Technical report (U.S. Army Engineer Waterways Experiment Station) ; HL-82-19.
Description: Technical Report
Abstract: Tests were conducted on a 1:30-scale model of Kahoma Stream to determine the adequacy of proposed channel improvements for Kahoma Stream and the offshore area. The model reproduced approximately 6,100 ft of Kahoma Stream and approximately a 350-ft-long by 500-ft-wide offshore area. The model was constructed so that the slopes of the high-velocity channel could be adjusted to reproduce various energy gradients equivalent to those resulting from different prototype Manning's η roughness factors. Unsatisfactory flow conditions were observed in the debris basin due to entrance conditions into the debris basin. Large cross waves were also present in the transition just downstream of the debris basin which resulted in pronounced superelevation of the water surface several hundred feet downstream in the high-velocity channel. A weir and transition design, which consisted of a three-sided weir with a wedge-type transition, was developed that provided satisfactory flow conditions in the transition, but little improvement in flow conditions was observed in the debris basin. Improvements in flow conditions in the debris basin were observed when debris was present in the basin resulting from debris tests or when the invert of the debris basin was unlined. The slopes of the high-velocity channel were initially adjusted to produce an energy gradient resulting from a Manning's η roughness factor of 0.015 in the prototype. Satisfactory flow conditions were observed in the high-velocity channel from the transition just downstream of the weir to the bridge transition at Cane Haul Road. However, flow conditions from Cane Haul Road Bridge to the downstream end of the channel were unsatisfactory due to the bridge transition design. This wedge-type transition design caused cross waves to develop in the transition and trapezoidal channel downstream. A warped-surface transition design with a 60-ft width significantly reduced the cross waves in the transition which provided satisfactory flow conditions throughout the transitions and trapezoidal channel. The slopes of the high-velocity channel were adjusted to reproduce the energy gradient resulting from a Manning's η roughness factor of 0.013 in the prototype. An increase in surface waves in some areas of the channel was indicated when compared with those measured with a channel slope simulating a Manning's roughness value of 0.015, but flow conditions were still satisfactory throughout the proposed high-velocity channel. Additional roughness placed on the channel invert downstream from Front Street Bridge for aesthetic purposes increased water-surface elevations that exceeded proposed wall heights between Front Street Bridge and the end of the trapezoidal channel. Raising the elevation of the left slope and placing a vertical wall on the right slope contained the increased water-surface elevation, thus providing adequate protection for this reach of channel. During a Standard Project Flood hydrograph, a large scour hole developed in the offshore area just downstream of the high-velocity channel and a considerable amount of deposition occurred between the two rock groins. Extending the trapezoidal channel and placing a boulder concrete section immediately downstream of the channel minimized the scour and deposition that occurred in the offshore area.
Rights: Approved for public release; distribution is unlimited.
URI: http://hdl.handle.net/11681/13439
Appears in Collections:Technical Report

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