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<br />tf <br /> <br />~ <br /> <br />-'- <br /> <br />TECHNICAL RELEASE 20 <br />COMPUTER PROGRAM FOR PROJECT FORMULATION <br />HYDROLOGY <br /> <br /> <br />CHAPTER 1. INTRODUCTION <br /> <br />This chapter describes the Computer Program for Project Formulation, <br />Hydrology (TR-20) in terms of the purpose~ computer requirements, and <br />availability of the program. The remaining chapters describe in detail: <br />the program organization, capabilities, and limitations; input preparation; <br />and output description. The appendices contain five sample jobs showing <br />different levels of complexity, blank input forms, a description of the <br />reach routing procedure and guidelines for rating curve coefficients and <br />reach lengths. <br /> <br />1.1 PROGRAM PURPOSE <br /> <br />The TR-20 computer program assists the engineer in hydrologic evaluation <br />of flood events for use in analysis of water resource projects. The <br />program is a single event model which computes direct runoff resulting <br />from any synthetic or natural rainstorm. There is no provision for <br />recovery of initial abstraction or infiltration during periods of no <br />rainfall. It develops flood hydrographs from runoff and routes the flow <br />through stream channels and reservoirs. It combines the routed hydrograph <br />with those from tributaries and computes the peak discharges, their <br />times of OCCUrrence and the water surface elevations at any desired <br />cross section or structure. Anyone of the above items can be printed <br />out as well as discharge hydrograph elevations, if requested. The <br />program provides for the analysis of up to nine different rainstorm <br />distributions over a watershed under various combinations of land <br />treatment, floodwater retarding structures, diversions, and channel <br />work. Such analysis can be performed on as many as 200 reaches and 99 <br />structures in anyone continuous run. The program uses the procedures <br />described in the SCS National Engineering Handbook, Section 4, Hydrology <br />(NEH-4) except for the reach flood routing procedure. The reach routing <br />is described in Appendixes G & H until Chapter 17, NEH-4 can be revised. <br /> <br />The program was originally developed by the Hydrology Branch of the Soil <br />Conservation Service (SCS) in cooperation with the Hydrology Laboratory, <br />