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<br />APPENDIX IV
<br />UNIT HYDROGRAPH COMPILATIONS
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<br />1. GENERAL. The planning and design of flood control and multiple-purpose projects involves exten-
<br />sive hydrologic studies in which unit hydrograph determinations are of great importance. The accuracy
<br />of spillway design flood, standard project flood, and project design flood estimates for many important
<br />projects is governed to a major extent hy the accuracy of the unit hydrographs used in the computations.
<br />Thc unit hydrograph procedure is also applicable to many hydrologic problems involved in interior drain-
<br />age investigations and similar studieso
<br />The determination of proper unit hydrographs for project, drainage areas is often complicated by the
<br />lack of reliable hydrologic records for the specific basins, In other cases, limitations in time preclude
<br />the derivation of unit hydrographs by detailed analyses of hydrologic records. To overcome these diffi.
<br />culties, insofar as practicable, and to provide a rational basis for adjustment of data from one station
<br />for application at adjacent locations, methods of deriving "synthetic" unit hydrograpbs have been de.
<br />veloped, which are based on correlations of certain drainage basin factors with observed runoff char-
<br />acteristics. In order to determine the accuracy and limitations of various synthetic unit hydrograph
<br />procedures, and to evaluate empirical coefficients involved in their application, unit hy.drograph determi-
<br />nations based on adequate hydrologic observations in a large number of drainage basins, ranging in size
<br />and runoff char,acteristics, are required. Inasmuch as the e.omputation of unit hydrographs from
<br />hydrologic records is a procedure that requires considerable time for the compilation and analysis of
<br />rainfall and runoff data, Division and District Engineers are requested to submit to the Chief of Engineers
<br />all reliable data on unit hydrographs that are assembled by their respective offices in connection with
<br />routine preparation of project reports.
<br />2. UNIT HYDROGRAPH FOUOS. Unit hydrograph determinations submitted to tbe Chief of
<br />Engineers have been processed by the District Engineer, Washington, D.C. as a part of Civil Works
<br />Investigation ]'1;0. CW-153. Those determinations found suitable for general distribution have been
<br />reproduced in Part II, Unit Hydrograph Compilations, Volumes 1,2, 3, and 4, the initial issue including
<br />data for drainage areas ranging from 50 to 3,000 square miles in size. The unit hydrograph determina-
<br />tions have been grouped geographically by Divisions as follows:
<br />Volume 1. New Engla,nd and North Atlantic Divisions.
<br />Volume 2. South Atlantic, Lower Mississippi Valley and Southwestern Divisions.
<br />Volume 3. Great Lake-s, Ohio River, Upper Mississippi Valley, and Missouri River Divisions.
<br />Volume 4, All of the above Divisions excepting Missouri River and I,ower Mississippi Valley
<br />Divisions.
<br />Copies of the folios listed above have been furnished to field offices engaged in Civil Works activities.
<br />Arca-di~tance curves, area-eleva.tion curves, and stream profiles were not included in data submitted
<br />by District Offiecs for some drainage basins, and therefore are not presented in the OW - [,<;3 compila-
<br />tions. In the event these missing data are now available in District Offices, or can be compiled with
<br />reasonable effort, they should be submitted to the Chief of Engineers, in order that appropriate additions'
<br />ean be made to the original data forms and revised sheets distributed for insertion in the folios.
<br />3.. UNIT HYDROGRAPH FORMS PREPARED BY SUBCOMMITTEE ON HYDROLOGY. FIARBC.
<br />Reference is made to Bulletin No.1, "Instructions for Compilation of Unit Hydrograph Data," prepared
<br />by the Subcommittee on Hydrology of the Federal Inter-Agency River Basin Committee, dated April
<br />1948 and distributed with the minutes of the 28th meeting of the subcommittee. Bulletin:-l o. 1 presents
<br />the recommendations of the Subeommitt(o(' on HydroloKv as to the content and form of unit hydrograph
<br />compilations with the iutrnt of systemizing thp: procedures and facilitating the exehange of data among
<br />Governffirll t agencies.
<br />U lIit h~'dl'Ograph data compiled by Federal ageneics represented on the Subcommittee 011 Hydrolog.,'
<br />llre bring presented in accordance with forms and instructions eontaiucd in Bull<,t,ill Xo, 1, ,insofar as
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