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32.3--1 WATER INFORMATION MANAGEMENT SYSTEM HANDBOOK Department of the Interior (USOI) Geological Survey. However, gaging stations operated by a State, an university, a water . conservancy district, a ditch company, the Forest Service, or some other organization may be appropriate. The important consideration is that the data be of good quality, of sufficient length, and accessible. Data from two types of gaging stations may be used in the procedure: representative and suitable gaging stations. A representative gaging station is one that is most similar hydrologically to the ungaged point(s) of quantification. This similarity should be expressed in hydrologic response rather than size. Therefore, consider elevation, geology, precipita- tion patterns, relief, and similar characteristics when select- ting a representative station. In addition, if a log-Pearson type III analysis is to be made, the representative gage station should have no more than 10 percent regulation upstream and a minimum of 10 years of record. Use data from the representative gage station to develop a normalized flow-duration curve and a normalized hydrograph. Suitable stations are all other stations that are similar to the ungaged point(s) of quantification, but are not so similar as to be selected as representative. The principal criteria for identifying which stations may be suitable for a particular point, or group of points of quantification, are amount of flow regulation and precipitation. For example, if the ungaged watershed(s) to be quantified has significant stream regulation (10 percent or more of the flow) in either withdrawals or augmentation, then the suitable gaged watershed(s) should have similar regulation. Remember, most gaging stations are located at controlled sec- tions; that is, at locations in the channel where either naturally, or through artificial intervention, channel cross section dimensions are not likely to change with time. All methods, except E, rely on the ability of a channel to adjust its boundaries in response to changes in frequent flows. As a result, it is usually impractical to measure channel charac- teristics at the gage station in the literal sense. Therefore, make channel measurements above or below the gaging site. ~ - Method A. Use Method A where. stream cross-sectional area and water surface slope can be measured at gaged sites and all points of quantification. *-FSH 4/89 AMEND 3-*