查看更多>>摘要：In response to recent and ongoing adaptation of culvert designs to environmentally sensitive installations, inlet loss coefficients and inlet control flow performance data are presented that are specific to environmentally sensitive culvert geometries. A common practice for such culvert designs is to bury the culvert inverts and create a simulated streambed through the culvert. Common cross-sectional geometries of such culverts typically include circular, elliptical, or pipe arch. These buried- or depressed-invert culverts create inlet geometries for which inlet loss information and inlet control flow performance curves have not been developed. Regardless of the method used to design environmentally sensitive culverts, the ability of the culvert to pass the design flood must be determined. In an effort to provide such information, an elliptical smooth-wall culvert with an invert burial depth of 50% was tested under various conditions (e.g., various end treatments, inlet and outlet control, submerged and unsubmerged inlet conditions, and ponded and channelized approach flow conditions) to determine the inlet loss coefficient and flow performance curve characteristics. The test results show that the inlet loss coefficient is relatively independent of both Reynolds number and the ratio of the distance from the inlet invert to the upstream total energy grade line to the culvert diameter (HW/D) and that the inlet loss coefficients for the elliptical culvert with 50% burial depth are approximately equal to the published coefficients for traditional culvert inlets. The inlet control data adapt well to the Form 1 and Form 2 unsubmerged and the submerged equations recommended by FHWA.
查看更多>>摘要：More than 47,000 culverts have been installed under the highways of Utah. The Utah Department of Transportation (DOT) maintains these culverts but has no comprehensive system for assessing condition and planning maintenance activities. Utah DOT initiated a study to determine the condition of its culverts by field surveys. The objective was to develop a system of qualitative and quantitative performance measures to assess both the long- and short-term behavior of highway culverts and to support the Utah DOT effort to modify and populate a computerized database designed to store culvert inspection data that can be used for statewide culvert asset management. Culvert management practices currently used by Utah DOT and other agencies are described. A total of 272 culvert inspections conducted during this project showed the inventory to be aging but not generally in need of immediate maintenance. The Utah DOT database, developed to track culvert condition, is effective but could be improved. Improvements would streamline both culvert inspections and priority ranking of culvert repairs. The FHWA system for rating culvert maintenance action was adopted, with a new proposed table for rating thermoplastic pipe. Culvert ratings were adjusted with an importance modifier that focused inspection and maintenance activity on critical culverts with higher consequence of failure. Critical culverts should be placed on a regular inspection schedule, whereas other culverts can be inspected during periodic roadway repaying or rehabilitation. Culvert inspection results will be added to the database to provide more insight eventually into culvert service life than is now possible.
Rollin H. HotchkissEmily A. LarsonDavid M. Admiraal
p.124-132页
查看更多>>摘要：Riprap and concrete stilling basins are often built at culvert outlets to keep high-energy flows from scouring the streambed. Two simple alternatives to large basins are examined: a horizontal apron with an end weir and a drop structure with an end weir. 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 research examines the jump geometry and 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 to 6.0. Both designs are effective in reducing outlet velocity 0.7 to 8.5 ft/s (0.21 to 2.59 m/s), momentum 10% to 48%, and energy 6% to 71%. The design layouts allow easy access for maintenance activities.
查看更多>>摘要："First flush" is a term for the initial period of stormwater discharge from a storm event. Conventional thinking is that the first flush exhibits high pollutant concentrations. The existence of a first flush in highway runoff has been documented through a comprehensive 4-year runoff monitoring from three highway sites in Los Angeles, California. As part of this study, a numeric definition of the mass first flush ratio is developed; it characterizes the normalized mass of pollutants in the first portion of the normalized runoff volume. Mass first flush ratios have been developed for more than 30 conventional water quality parameters, heavy metals, nutrients, and organic pollutants. This study explores the improved performance that some best management practices (BMPs) exhibit when they can take advantage of the high concentrations of pollutants at the beginning of a storm event. A range of hypothetical events corresponding to the observed mass first flush ratios were simulated. These simulations demonstrate that improved mass removal rates are possible when BMPs can be managed to treat a greater volume of the early runoff. For example, it was shown that for pollutants such as total suspended solids, chemical oxygen demand, total organic carbon/compounds, and oil and grease, infiltration basins that can capture the first 20% of the storm volume and bypass the remaining volume can be twice as effective as a practice that treats 20% of the storm volume throughout the entire period of runoff. Similarly, when a seasonal first flush exists, treating the first few storms of the season entirely is more effective than treating a constant volume throughout the season.
NETL
NSTL