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Chatfield Reservoir Water Budget

Chatfield Reservoir Water Budget. Jim Saunders and Jamie Anthony WQCD, Standards Unit 13 Dec 2007. Roadmap for Technical Review. Purpose of Water Budget. Identify and quantify flow sources Rank sources in terms of importance (for determining phosphorus concentrations and loads)

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Chatfield Reservoir Water Budget

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  1. Chatfield Reservoir Water Budget Jim Saunders and Jamie Anthony WQCD, Standards Unit 13 Dec 2007

  2. Roadmap for Technical Review

  3. Purpose of Water Budget • Identify and quantify flow sources • Rank sources in terms of importance (for determining phosphorus concentrations and loads) • Aim is to understand hydrology well enough to support development of a phosphorus budget

  4. Inflows • USACE computed inflow is “gold standard” • Surface inflows • Gaged (South Platte, Plum Creek) • Ungaged (Deer, Massey) • Direct runoff • Alluvial inflow (chiefly Plum Creek) • Direct Precipitation

  5. Gaged Surface Inflows

  6. Add Precip (directly to surface)

  7. What’s Left?...~7% • Ungaged surface flow, mostly from low elevation • Alluvium • Both are more likely to be controlled by factors in common with Plum Creek than with the South Platte

  8. Further Parsing of Flows • Strong association between Plum Creek and residuals; slope and intercept useful

  9. Interpreting Graphs Intercept is residual when no flow in Plum; =alluvium Slope is proportional increase in Plum Cr runoff; =ungaged area

  10. Overview of Graphical Analysis

  11. Take Home from Graphs • Parsing a very small % of inflow (~7%) • Alluvial contribution (intercept) relatively stable; use constant for each 5-y block • Added runoff (slope) similar to ungaged area (24% of Plum Creek area) for first 20 years • Trend in slope over last decade is puzzling; we’re still seeking an explanation

  12. Chatfield Annual Water Budget

  13. Conclusions and Comments • Water budget provides a solid basis for estimating phosphorus loads • Some snags with high resolution approach (measured inflows tended to exceed computed inflows in last 10 years), but still a solid basis • Alternative could be developed on basis of two gages and precip (>90% of computed inflow) • Fortunately, uncertainty affects only very small components of inflow • Open to ideas about approach

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