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001006 31.31b WATER INFORMATION MANAGEMENT SYSTEM HANDBOOK 31.3 - Data Needs. Maintenance flow quantification requires some basic nyarologic data. These include streamflow, channel geometry, and watershed characteristics data. ( \ It is neither practicable nor reasonable, however, to presume that streamflow data is necessary on all channels administered by the USDA Forest Service before such channels can be managed so as to secure a favorable condition of water flows. Therefore, the procedure is designed to achieve the favorable flow objective without the benefit of on-site data. 31.31 - Streamflow Data. Obtain data for as many streamflow gaging stations as practical within the area to be quantified. In most cases, the USDI Geological Survey will be the only available source of these data. 31.31a - Criteria. Streamflow data utilized in the analysis should meet the following criteria: 1. Flow regimes described by gaging station data should be representative of areas where maintenance flows will be calculated. 2. Data should consist of at least a representative 10 years of record. 3. Gaging stations used in the analysis of unregulated watersheds should have less than 10 percent of the total annual flow volume above the gaging station diverted or regulated. 4. Data sets utilized should, as much as practicable, represent long term average conditions. 31.31b - Gaging Station Data. The following data should be obtained for each gaging station. However, not all methods require all listed data items. 1. LOg-Pearson type III flood frequency analysis for the period of record. 2. Log-Pearson type III low flow frequency analyses for 1- , 3- , 7- , 14- , 30- , and 90-day low flows. 3. Selected basin characteristics [such as mean basin elevation, and drainage area]. 4. Flow duration data of daily mean discharges for period of record. i. Mean ann4al discharge. 1D No. 1 9/10/85