Category: Hydraulics

Various types of drainage facilities are required to protect the highway against surface and subsurface water. Drainage facilities must be designed to convey the water across, along, or away from the highway in the most economical, efficient, and safe manner without damaging the highway or adjacent property. The purpose of this manual is to provide detailed information on the subjects of hydrologic and hydraulic analysis related to highway design. This manual should be used in conjunction with the Washington State Department of Transportation (WSDOT) Highway Runoff Manual and the WSDOT Design Manual, specifically Section 1210.

Category: Hydraulics Mean Annual Runoff

Sometimes it is necessary to determine the mean annual flow or runoff for a given stream. When published flow records are available they are the best source of information. Minor streams which do not have any gaging records available can be estimated by the following procedure: Metric Units and English Units

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Category: Hydraulics Flood Reports

Flood reports have been developed for many rivers in Washington State. Most of these reports, and the ones that are most readily accessible, have been developed by the Federal Emergency Management Agency (FEMA). Other reports have been developed by the United States Army Corps of Engineers and by some local agencies. These reports are a good source of flow information

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Category: Hydraulics USGS Regression Equations

While measured flows provide the best data for design purposes, it is not practical to gage all rivers and streams in the state. A set of equations have been developed by the USGS to calculate flows for drainage basins that do not have a streamflow gage. The equations were developed by performing a regression analysis on streamflow gage records to

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Category: Hydraulics Published Flow Records

When available, published flow records provide the most accurate data for designing culverts and bridge openings. This is because the values are based on actual measured flows and not calculated flows. The streamflows are measured at a gaging site for several years. A statistical analysis (typically Log Pearson Type III) is then performed on the measured flows to predict the

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Category: Hydraulics Santa Barbara Urban Hydrograph Method

When designing flood control structures and some stormwater treatment facilities, the designer must know more than just the peak flow that will occur. Along with the peak flow, the volume of runoff must be calculated as well as the relationship between time and the rate of runoff. The only way to accomplish this is to use a method of analysis

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Category: Hydraulics The Rational Method

General The rational method is used to predict peak flows for small drainage areas which can be either natural or developed. The rational method can be used for culvert design, pavement drainage design, storm drain design, and some stormwater facility design. The greatest accuracy is obtained for areas smaller than 40 hectares (100 acres) and for developed conditions with large

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Category: Hydraulics Drainage Basin

The size of the drainage basin is one of the most important parameters regardless of which method of hydrologic analysis is used. To determine the basin area, select the best available topographic map or maps which cover the entire area contributing surface runoff to the point of interest. Outline the area on the map or maps and determine the size

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Category: Hydraulics Selecting hydrology analysis method

Each of the first five methods listed above are appropriate to use for different design conditions and none of the methods will cover all situations. The first step in performing a hydrologic analysis is to determine which method is most appropriate. Generally there is no need to select more than one method. 1. Rational Method: This method is used when

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