Library builder

The time of concentration or rainfall duration is equivalent to the length of time it takes for the runoff to travel from the most remote point of the watershed to the point of solution. This assumes that there is a uniform rate of rainfall over the entire water­shed resulting in the maximum flow at the […]

Where there are no or insufficient stream-gauging records available, peak-flow methods such as the “rational method” and the Natural Resources Conservation Service (NRCS) method may be used. The rational method is the most common procedure for determin­ing the quantity of flow for the design of minor hydraulic structures. Its use in the United States dates […]

Estimating the peak discharge for which highway drainage structures are to be designed is one of the most common problems and biggest challenges faced by the highway engineer. The problem may be separated into two categories: (1) watersheds for which historical runoff data are available, those with gauged sites, and (2) areas for which no […]

There are two accepted alternatives for determining the design flood frequency at a specific site: (1) by policy and (2) by economic assessment. An example of an estab­lishment of a design flood frequency by policy is the Code of Federal Regulations, which specifies that the design flood for encroachment onto through lanes of interstate highways […]

Characteristics of the watershed area directly affect the hydrologic analysis. Basic fea­tures of the watershed basin include size, shape, slope, land use, soil type, storage, and orientation. The size of the watershed basin is the most important characteristic affecting the determination of the total runoff. It is generally measured in acres, square miles, or square […]

The science of hydrology is concerned with the estimation of the intensity of rainfall, thedistribution of the flow of the rainwater over the land, and the determination of the flow quan-tity (peak and total) that eventually reaches some specified point, the “point of solution.” Of primary concern to the highway engineer is the frequency of […]

Principal Hydraulic EngineerE. L. Robinson EngineeringColumbus, Ohio A properly designed highway requires a well-designed drainage system. This requires a determination of the quantity of runoff reaching the drainage structures and an accurate analysis of water flow through the structures in order to properly size them. Also, a working knowledge of structural characteristics of buried pipe […]

In recognition of the serious potential destructive effects of earthquakes, AASHTO specifications contain comprehensive provisions for seismic design. Although earlier speci­fications contained some provisions, the more comprehensive provisions were not adopted until the 1980s. They were based on a detailed study by consultants who were specialists in that field, with review and participation by bridge […]

In the design of a new bridge, provision must be made for maintenance inspection. For example, plate girders can be provided with safety handrails, safety railings can be specified on top of wide piers for inspectors to check bearings, and safety ladders can be installed to provide access to elements of the bridge otherwise difficult […]

For concrete-slab bridges where expansion is not provided, the slab is normally sup­ported directly on the substructure, concrete on concrete. A “centerline of bearing (singular)” is denoted on plans at each support. (Some states do not identify a centerline of bearing at the end bent of a slab bridge. Instead, they measure the end span […]