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Memo: Seneca II AHR - 2 - April 8, 1986 Group 1 SW-S2-5 Group 2 NPDES 004 SW-S2-1 SW-S2-6 NPDES 002 NPDES 003 SW-S2-2 The stations are grouped by receiving stream for maximum information barring any unforeseen problems during sampling. Time constraints would probably preclude monitoring both groups within a single day. 3. With the reduction to a tri-annual monitoring program, is the sampling schedule for full-list analysis determined by time (seasonal) or flow conditions? If a mean annual representation is desired, sampling at intervals throughout the year based on seasonal differences would be preferred. If monitoring is to determine extremes of water quality, then a flow-dependent sampling is required. This could be further defined into: 1. Low flow, cold temperature; 2. High flow, cold or warm temperature; and, 3. Low flow, warm temperature, when only three samples are allowed on an annual basis. Condition No. 2 could be either a snowmelt event or a storm runoff event. I was unable to determine from available correspondence which objective was defined for monitoring under the reduced program. My preference would be to sample based on extremes of flow. A clarification on this and a statement at the beginning of discussion in Section V would be appreciated. 4. 'Stage-rating curves were included in the report as in 1984. The use and purpose of these is uncertain. The gages constructed at surface sites are of the crest-stage type which implies they are used for estimating unmonitored data alone. Is this correct? The ratings are said to be based on Manning equation velocities, of which no indication of Manning "n" value is supplied in the report, or if different n estimates are used as channel conditions change between high and low flows. As Manning's n cannot be directly measured, then its use can give only a very approximate estimate of flow for rating a station. A more valid procedure for developing a stage-rating curve, if needed, would employ a step-backwater analysis. Without going to this extent, however, the existing curves could be improved by obtaining more calibration points at high and low flows, periodic updating of the curve with recent observations, and/or adjusting the best fit line into a curve at the lower end. If a considerable improvement in station flow monitoring is desired, then construction of a weir or other control along with continuous recorder is advised to improve discharge monitoring. In future AHR's, the rating curves should be relocated to Appendix D or omitted rather than included in the discussion section of the report. 5. The daily flow tables could be improved by also calculating an annual mean flow (in cfs) and an annual summation of flow volume (in acre-feet). This would supplement reporting of flow conditions year-to-year in quantitative terms and assist in the narrative discussion in the AHR.