Theodore G. Cleveland

Updated Rainfall Coefficients for Texas—The EBDLKUP-NEW.XLS Tool

EBDLKUP.xls is a spreadsheet tool in current use by the Texas Department of Transportation (TxDOT) engineers and other design engineers for estimating intensity-duration-frequency (IDF) of design rainfall by county; the tool differs from discrete-duration IDF in that it facilitates estimation for real-value durations (not discrete durations). This real-value duration capability is a great utility tool for many hydrologic methods such as the rational method. The rainfall coefficients ( E , B , and D ) for the spreadsheet were created by interpreting the rainfall depth contours by duration and frequencies from research by the National Weather Service completed in the early 1960s and augmented in the 1970s. (TP-40 Hershfield, 1961; NWS Hydro-35, 1977). Recent research projects sponsored by TxDOT have produced newer knowledge related to rainfall depths from longer rainfall records, newer statistical methods, and improved presentation methods. The results of these studies are incorporated into a new tool EBDLKUP-NEW.xls . The new tool was designed to maintain a similar interface and data structure to ensure that the revised coefficients can be inserted into existing design software (GeoPack-Drainage, WinStorm, and other drainage design tools that directly use the E , B , and D values). Added features include embedded depth-duration-frequency (DDF) estimates for use with a companion tool to parameterize empirical Texas hyetographs, embedded documentation, and embedded video training. This paper presents the new tool, the underlying database analysis, and the embedded training concept.

TXHYETO.XLS: A Tool to Facilitate Use of Texas-Specific Hyetographs for Design Storm Modeling

EBDLKUP.xls is a spreadsheet tool in current use by the Texas Department of Transportation (TxDOT) engineers and other design engineers for estimating intensity-duration-frequency (IDF) of design rainfall by county in Texas; the tool differs from discrete-duration IDF in that it facilitates estimation for real-value durations (not discrete durations). Research projects sponsored by TxDOT produced newer knowledge related to rainfall depths and the results of these studies are incorporated into a new tool EBDLKUP-NEW.xls projected for deployment in 4th Quarter of 2015. Added features are imbedded depth-duration-frequency (DDF) estimates for use with a companion tool TXHYETO.XLS to parameterize empirical Texas hyetographs, and imbedded documentation, including imbedded video training. The paper presents the companion tool, TXHYETO.XLS that simplifies the task of using the Texas dimensionless hyetographs; An example of tool use is presented - combined the two tools enhance hydrologic design capability for instances where either a single intensity is needed (EBDLKUP-NEW.XLS), or where an entire design hyetograph is needed (TXHYETO.XLS).

Simple Rainfall Loss Models for Rainfall-Runoff Modeling

Unit hydrographs are developed for a specific watershed using two basic approaches. If unit rainfall-runoff data are available, then numerous techniques can be applied to estimate a unit hydrograph from the data. If no data are available, then methods of synthetic hydrology must be applied. Current practice is regionalization of measured behavior used to transfer known hydrographs (or other hydrologic entities) from a location where measurements are available to unmonitored watersheds. The regionalization involves determining time parameters for the unit hydrograph procedure, which may include time to peak, time base, or time of concentration. Regionalization also involves development of regional regression equations for time parameters, watershed and/or rainfall characteristics. The principal elements required for the synthetic approach are the determination of characteristic loss features (loss model) and characteristic response time (unit hydrograph model). The authors observe that even if the temporal redistribution of excess rainfall is performed using hydraulic models, which is certainly feasible and often the most appropriate approach, then there is still need to understand how to convert the rainfall signal into an excess rainfall signal, and this will be accomplished with some kind of loss model. In the collective literature losses are correlated with watershed soil properties, while the characteristic response time is associated with physical characteristics such as watershed drainage areas, main channel and overland flow slopes, characteristic lengths, and characteristic velocities. Unit hydrograph parameterization was examined based on topographic information and simple loss models to predict the runoff volume, rate and timing with minimal watershed characterization, using data readily available to drainage engineers. Results from the approach were compared with observed rainfall-runoff responses and are reported herein.