Summary of dimensionless Texas hyetographs and distribution of storm depth developed for Texas Department of Transportation research project 0–4194

Hyetographs and storm depth distributions are important elements of hydraulic design by Texas Department of Transportation engineers. Design hyetographs are used in conjunction with unit hydrographs to obtain peak discharge and hydrograph shape for hydraulic design. Storm-depth distributions can be used to assess the probability of a total rainfall depth for a storm. A research project from 2000–2004 has been conducted to (1) determine if existing Natural Resources Conservation Service (NRCS) dimensionless hyetographs are representative of storms in Texas, (2) provide new procedures for dimensionless hyetograph estimation if the NRCS hyetographs are not representative, and (3) provide a procedure to estimate the distribution of storm depth for Texas. This report summarizes the research activities and results of the research project. The report documents several functional models of dimensionless hyetographs and provides curves and tabulated ordinates of empirical (nonfunctional) dimensionless hyetographs for a database of runoff-producing storms in Texas. The dimensionless hyetographs are compared to the NRCS dimensionless hyetographs. The distribution of storm depth is documented for seven values of minimum interevent time through dimensionless frequency curves and tables of mean storm depth for each county in Texas. Conclusions regarding application of the research results are included in the report.