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31.32 001578 WATER INFORMATION MANAGEMENT SYSTEM HANDBOOK 6. Daily mean hydrograph for the period of record. 7. Stage-discharge relationship. 8. Hydraulic geometry of the station cross section including bankfull width and water surface slope at bankfull discharge. 9. Field measured bankfull discharge. 10. Velocity as a function of discharge. Most of the data and analyses listed above are available from the USDI Geological Survey WATSTORE assistance centers or local state offices (sec. 30.72). Some data and analyses can also be obtained directly using the Flow Data file of the EPA STORET system. 31.32 - Channel Geometr and Basin Characteristics. Data for channel geometry an basin characteristlcs are not genera y available and must be measured in the field or interpreted from maps. Appendix C, sec. 36.3, describes the measurement of bankfull channel top width. Items such as weighted mean basin elevation are well destribed in hydrologic literature and are not repeated here. Caution must be exercised if the USDI Geological Survey basin-characteristics method is being used rather than a locally developed relationship. Any basin characteristic used must be quantified in accordance with the procedures described in the parent USOl Geological Survey document. 31.33 - Field Measurements. The importance of field data to support the calculation of required maintenance flows is especially important in cases where legal challenge or controversy may arise. Collect field data to establish the local relationships used, to support the decisions underlying the application of the procedure, and to verify the calculated maintenance flow requirements. Visit the watershed and the stream channel site to be quantified if possible. Prepare photo documentation of stream and channel conditions and a brief description of the capacity of the stream bed and/or banks to adjust their dimensions in response to frequent flows. 32 - PROCEDURE FOR MAINTENANCE FLOW QUANTIFICATION FOR SNOWMELT DOMINATED PERENNIAL STREAMFLOW. Use gaging station data and the appropriate application of statistical techniques to develop basic relationships that can be extrapolated to ungaged watersheds. Calculate the bankfu1 discharge for the ungaged point of Quantification by applying these relationships. This value can then be used, along with gage station records, to schedule a range and duration of required maintenance flows.