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<br />32.lle <br /> <br />001582 <br /> <br />WATER INFORMATION MANAGEMENT SYSTEM HANDBOOK <br /> <br />watershed area or other appropriate basin characteristics. With the <br />relationship developed, watershed area or other basin characteristics above <br />the point of quantification are used to directly calculate a log-Pearson <br />type III peak flow approximately equivalent to bankfull discharge. <br /> <br />32.11e - Method E. Apply Method E to those channel reaches which do not <br />adjust their dimension in response to changes in frequent flows. An <br />abbreviated flow requirement is developed which eliminates certain portions <br />of the calculated channel maintenance hydrograph. <br /> <br />32.2 - Station Selection. All five analysis methods use certain basic <br />relations to calculate bankfull discharge at the ungaged point(s) of <br />quantification. These relations are developed from the available gaging <br />station data. Gaging stations used in this procedure will most commonly be <br />operated by the USDI Geological Survey. However, gaging stations operated <br />by a state, an university, a water conservancy district, a ditch company, <br />the USDA Forest Service, or some other organization may be appropriate. <br />The important consideration is that the data be of good quality, of <br />sufficient length and accessible. <br /> <br />Data from two types of gaging stations may be used in the procedure: <br />representative and suitable gaging stations. A "representative" gaging <br />station is one that is most similar hydrologically to the ungaged point(s) <br />of quantification. This similarity should be expressed in hydrologic <br />response rather than size. Therefore, consider elevation, geology, <br />precipitation patterns, relief, and similar characteristics when selecting <br />a representative station. In addition, if a log-Pearson type III analysis <br />is to be made, the representative gage statipn should have no more than 10 <br />percent regulation upstream and a minimum of 10 years of record. Use data <br />from the representative gage station to develop a normalized flow-duration <br />curve and a normalized hydrograph. <br /> <br />"Suitable" stations are all other stations that are similar to the ungaged <br />point(s) of quantification, but are not so similar as to be selected as <br />representative. The principle criteria for identifying which stations may <br />be suitable for a particular point, or group of points of quantification, <br />are amount of flow regulation and precipitation. For example, if the <br />ungaged watershed(s) to be quantified has significant stream regulation (10 <br />percent or more of the flow) in either withdrawals or augmentation, then <br />the suitable gaged watershed(s) should have similar regulation. <br /> <br />Remember, most gaging stations are located at controlled sections; that is, <br />at locations in the channel where either naturally, or through artificial <br />intervention, channel cross section dimensions are not likely to change <br />with time. All methods, except E, rely on the ability of a channel <br />