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<br />CHAPTER 1. INTRODUCTION <br /> <br />Various hydrologic processes contribute to the formation of a runoff <br /> <br /> <br />hydrograph resulting from rainfall and snowmelt on a watershed. The <br /> <br /> <br />study of these processes and the determination of the key parameters affec- <br /> <br /> <br />ting them give insight to hydrograph production. This volume will describe <br /> <br /> <br />certain methods of deriving fundamental hydrologic parameters from observed <br /> <br /> <br />events, and will suggest techniques of utilizing these deduced parameters <br /> <br /> <br />in the hydrologic design of water resource developments. It presents some <br /> <br /> <br />highly useful and up-to-date procedures concerned with hydrograph analysis, <br /> <br /> <br />with emphasis devoted to areas where the quantity of hydrologic data is <br /> <br /> <br />limited. Several of these procedures are illustrated in sufficient detail <br /> <br /> <br />to facilitate a thorough understanding, not only of the principles and <br /> <br /> <br />procedures, but of application and the management of the basic data as <br /> <br /> <br />well. Although the emphasis in this volume is placed on computer-oriented <br /> <br /> <br />techniques, it is recognized that these same techniques may not be as use- <br /> <br /> <br />ful when electronic computers are not readily available. Accordingly, <br /> <br />Appendix 1 describes some techniques that are oriented toward desk calcu- <br /> <br /> <br />lator use. Where pertinent, certain generalized hydrologic engineering <br /> <br /> <br />computer programs that have been found to be useful to the engineer engaged <br /> <br /> <br />in water resource studies are described, and two of them are included as <br /> <br /> <br />appendices to this volume. <br /> <br /> <br />This volume is not intended to be a compendium of available methods. <br /> <br /> <br />The methods presented have been selected for their applicability to the <br /> <br /> <br />more frequent types of problems encountered in hydrograph analysis. While <br /> <br /> <br />it is known that many of these techniques contain assumptions (such as <br /> <br /> <br />linearity) that do not accurately describe the processes actually occur- <br /> <br /> <br />ring in nature, experience has shown that these assumptions need not be a <br /> <br /> <br />major handicap, considering the quality of the basic data that are usually <br /> <br /> <br />available, and provided that the techniques are applied with judgment and <br /> <br /> <br />understanding of the assumptions. In addition, many of the functions <br /> <br /> <br />described in this volume are based in part on the fact that the hydrologic <br /> <br /> <br />quantities utilized in hydrograph analysis are averaged or "lumped" for <br /> <br /> <br />computation purposes. This assumption can severely limit the techniques <br /> <br />1-01 <br />