Estimation of Design Storm and Design Flood

Standard methods/models for flood estimates in gauged catchments are described in various textbooks on hydrology and manuals of the Central Water Commission (CWC) in India. But industrial sites are generally located in small ungauged catchments and generally have a source of water from ungauged catchments. Therefore, this chapter focuses on the methods of flood estimation in ungauged catchments with illustrative examples. This chapter begins with examples on the probability of hydraulic events, followed by an explanation of probable maximum flood (PMF), standard project flood (SPF), isopluvial maps, return period flood, and criteria for design flood for various types of hydraulic structures. Examples on the estimation of 1-day and 2-day annual maximum rainfall of various return periods for the hydrologic design of a solar park are given. Design storm computation and application of the unit hydrograph (UH) method of flood estimation are illustrated with an example. Regional flood formula and synthetic unit hydrograph (SUH) methods are commonly used in India for flood estimation in ungauged catchments. The methods are illustrated with examples. The CWC, in association with other agencies, has prepared Flood Estimation Reports for 26 hydro-meteorologically homogenous subzones of India (Website https://www.w3.org/1999/xlink" xlink:href=" https://cwc.gov.in/regional-flood-estimation-report "> https://cwc.gov.in/regional-flood-estimation-report ). These reports elaborate the SUH method for flood estimation and provide isopluvial maps of 24-hour rainfall for 25-, 50-, and 100-year return periods. Design storm analysis is explained with an example of a solar park in the Luni River basin in India. The rational method, updated and modified for catchments in India, is popularly used for the estimation of floods in small catchments (less than 25 km)