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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


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  Full Article…


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  Full Article…


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  Full Article…


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  Full Article…


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  Full Article…


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  Full Article…


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:  Full Article…


General Hydrology

The Washington State Department of Transportation (WSDOT) Olympia Service Center (OSC) Hydraulics Branch uses several methods of determining runoff rates and/or volumes. Experience has shown them to be accurate, convenient, and economical. The following methods will be discussed in detail in subsequent sections of this chapter 1. The Rational Method 2. The Santa Barbara Urban  Full Article…


Construction Value engineering

In our consideration of the role of the project planner and designer, we have discussed the importance of constructability analysis and value engineering. Formal value engineering is an essential activity throughout the construction process as well. In this process, the contractor is invited to suggest changes to the design that will result in cost savings;  Full Article…


Construction Cost-estimating software

The process described above for compiling construction cost estimates might be described as simple, routine, time consuming, even boring, but also essential, with requirements for accuracy, organisation, no omissions and no duplications. The spreadsheets used to prepare Tables 4.1 through 4.4 are examples of the use of information technology to manage effectively and efficiently the large amounts of  Full Article…


A unit-price/measure-and-value example

Our second example of a cost estimate is for the construction of an embankment and roadway. Once again, the example is oversimplified but still includes the basic concepts. In this example, the result of our effort will be a series of unit prices for each of the specified bid items, as required by the tender  Full Article…


Construction A lump-sum/fixed-price example

Consider a ‘project’ that will construct a cast-in-place concrete foundation wall, as shown in Figure 4.5. We desire to compile a single price for submittal to the owner for this lump-sum contract. The work will consist of mobilisation; clearing and grubbing an area of 400m2; excavating through silt and rock to a depth of 400  Full Article…


Construction Subcontract work

The final category of direct cost includes work that will be performed by subcontractors. Typically these are specialty contractors that will sign a contract with the general contractor for work in such areas as painting, plumbing, electrical work, concrete finishing and traffic control, if their proposals are accepted and if the general contractor is chosen.  Full Article…