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SUMMARY OF FINDINGS

SUMMARY OF FINDINGS. COHYST Pilot Project Wood River Watershed Surface Runoff Model COHYST Technical Committee Update January 19, 2010. PILOT STUDY OBJECTIVES.

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SUMMARY OF FINDINGS

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  1. SUMMARY OF FINDINGS COHYSTPilot ProjectWood River WatershedSurface Runoff ModelCOHYST Technical Committee UpdateJanuary 19, 2010

  2. PILOT STUDY OBJECTIVES • Develop and perform a pilot test of a spatially-distributed, CN-based rainfall-runoff model for the COHYST area that can predict the impacts of land use changes on edge-of-field runoff from rainfall. • Team selected Wood River Watershed above Alda • Assess whether COHYST calibration is creating or destroying water. • What do the findings imply regarding use of CN method in future COHYST (and Conjunctive Management) work?

  3. “Primer” on CN Method This project status report does not include a presentation of the CN method, but a set of slides is included at the end for anyone wanting a brief overview of the method.

  4. Presentation format • Too Much Info to Cover Everything • Focus on Key Findings vs. Details • Include “Samples” of .xls tables • Jump to .xls files as needed at T.C. • Refine for “Condensed” Presentation to Sponsors • Need for Final Report

  5. PROJECT BACKGROUND • July 12, 2007 PPT* on Surface Water Modeling to Sponsors – Four Options • Sponsors Oked Option 3 – “Weekly,” but no Routing • Selection of Pilot Watershed • Subcommittee Formed, J.B., R.V., R.K. • Selected two 7-yr G.S. Tests, 1964-1970, 1999-2005 • GIS Work Completed by Rick V. • Spreadsheet Work by J.B./G.L. • Several Progress Reports to T.C. *Attached at end of this PPT for reference.

  6. HANDOUTS TODAY • Inventory of Key Spreadsheets and Contents • Original Scope of Work • Descriptions of Six “Tests” with Commentary • Copies of Slides not Provided but are Available on the ftp Site All posted on ftp site under “Wood River Pilot Study/New Folder”

  7. METHODOLOGY PILOT TEST OF CN • Determine total daily edge-of-field runoff above stream gauges by CN method • Identical to method used in Cropsim • Estimate direct runoff (D.R.) from USGS discharge records (requires base flow estimate) • Compare Nos. 1 and 2 for annual, seasonal, monthly, all single runoff-rainfall events, and individual, single events • “Success” measured by results of No. 3 Comparison of CN results with gauged flows is considered better at Riverdale vs. Alda because there is little or no base flow evident at Riverdale.

  8. BASE FLOW AT RIVERDALE AND ALDA? Groundwater elevations provided by CPNRD, field surveying provided by NDNR, all in NGVD 88. Data suggests that there is little (if any) Darcy-induced base-flow in the Riverdale and Gibbon gauge readings, and possibly at Alda. Small continuous releases by the Gibbon Wastewater Plant probably reach the Alda Gauge during wet periods.

  9. Wood River Watershed

  10. CN MODEL 2001* CALMIT LAND USE CLASSIFICATIONS *2001 Calmit data used for both 7-yr study periods

  11. KEY QUESTIONS ANSWERED TODAY • What were the results of comparing the edge-of-field runoff by the CN method with gauged flows (and estimates of direct runoff) at Riverdale and Alda? • Annual? • Growing Season? • Monthly? • By “Identifiable” Events as a group? • By individual “Identifiable” Events? • What do the findings imply regarding future COHYST (and Conjunctive Management) work? Key results spreadsheets are posted on ftp site under “Wood River Pilot Study.”

  12. “IDENTIFIABLE” RUNOFF-RAINFALL EVENTS • Definition: • Stand-alone runoff events with 1- to 10-day rain, and no apparent AMC I, III “Problem” • Identification: • Use WHAT estimates to identify dates of direct runoff hydrographs (0.0 to 0.0 cfs) • Examine daily precipitation to assess amounts of rainfall that produced each hydrograph *The “AMC I, III Problem” is described in detail later.

  13. sample OF “Identifiable” runoff-rainfall event at Riverdale

  14. “IDENTIFIABLE”* RUNOFF-RAINFALL EVENTS • Riverdale Gauge, 1964 – 1970 35 Events • Alda Gauge, 1964 – 1970 6 Events • Alda Gauge, 1999 – 2005 15 Events *Isolated runoff event with 1- to 10-day rain, and no apparent “AMC I, III Problem.”

  15. REVIEW – TESTS CONDUCTED • Test #1:  Run the Riverdale runoff model for the 1964-1970 growing seasons with the 3-day “irrigation algorithm” applied to all lands classified as irrigated • Test #2:  Run the Riverdale runoff model for the 1964-1970 growing seasons without the irrigation algorithm • Test #3:  Run the Alda runoff model for the 1964 – 1970 period with the irrigation algorithm on all lands classified as irrigated • Test #4:  Run the Alda runoff model for the 1964 – 1970 period without the irrigation algorithm  • Test #5:  Run the Alda runoff model for the 1999 – 2005 period with the irrigation algorithm on all lands classified as irrigated • Test #6: Run the Alda runoff model for the 1999 – 2005 period without the irrigation algorithm •  Test #6a: Run the Alda model for the 1999 – 2005 period with all land classified as irrigated converted to “native” conditions (pasture & rangeland) • Test #6b: Run the Alda model for the 1999 – 2005 period with all crops (irrigated and dryland) converted to “native” conditions (pasture & rangeland)

  16. ALGORITHM DEFININTIONS Two algorithms were used for CN modeling, and assessments of each are described later: • AMC I, II, III Algorithm with Discrete CNs • Irrigation Algorithm for Irrigated Crops

  17. Scs AMC I, II, III GROWING SEASON algorithm*Applied Daily 5-day Antecedent P: P < 1.4” 1.4” < P < 2.1” 2.1” < P Then: Switch CN to AMC I Switch CN to AMC II Switch CN to AMC III *Algorithm used in both Cropsim and COHYST.

  18. AMC I, II, III CONVERSION TABLE

  19. BEST FIT EQS* TO AMC I, II, III TABLES • Curve Number Conversion: AMC II to AMC I CN1 = CN2 / (2.281-(0.0128*CN2)) • Curve Number Conversion: AMC II to AMC III CN3= CN2/ (0.427+ (0.0057* CN2)) *Used in both CROPSIM and Pilot Study

  20. LITERATURE ON AMC I, II, III METHOD • Data for published tables “cannot be found.” • AMC classes I, II, III “abandoned” by NRCS in 1993. • Application is widespread but “discouraged” • Instead, NRCS recommends 2008 ARC I, II, III Curves based on frequency of runoff event • Can also use soil moisture accounting such as in SWAT where ARC I and III are the soil’s wilting point and field capacity, respectively.

  21. “IRRIGATION ALGORITHM” The edge-of-field runoff for both the Riverdale and Alda watersheds was modeled with and without the “irrigation algorithm” running. The following steps were used in the irrigation algorithm: • For irrigated crops only, if the previous 4-days’ ∑ P ≤1”, add 0.33” to the precip, P, each day for 3 days • Include the 0.33” amounts to the AMC algorithm’s 5-day count, then test for any changes in AMC • Change the AMC to I, II, or III if the 5-day precip count with the added “irrigation” water met any of the three AMC ranges • Delete the 0.33” amounts before determining runoff by CN • Wait at least 4 days before turning the algorithm on again (Note: Tests with this showed that about 10 applications of irrigation water would occur during the growing season)

  22. SUMMARY OF FINDINGSWith and Without Irrigation Algorithm • RIVERDALE SUBWATERSHED RESULTS, 1964-1970 • ALDA WATERSHED RESULTS, 1964-1970 AND 1999-2005 • COMPARISONS OVER BOTH PERIODS, AND BOTH AREAS ’64-’70

  23. STUDY RESULTS Riverdale Subwatershed • CN-Based Annual Estimates of Runoff Compared to Gauged Values • Totals During all 7 Growing Seasons • By Individual Growing Seasons • Monthly • By Each Set of “Identifiable” Events • By Individual “Identifiable” Events

  24. FINDINGS: BASEFLOW QUESTION RIVERDALE GAUGE • Total gauged flow for entire 1964-1970 growing seasons = 42,700 af • WHAT method estimated base flow = 12,294 af (29%) • WHAT method direct runoff = 30,406 af (71%) • CN model with irrigation estimated edge-of-field runoff = 40,911 af (96%) Observations: Even though not supported by elevations, fact that EOF < Gauge suggests there may be “base flow” at Riverdale; for single “identifiable” rainfall-runoff events, WHAT method runoff much better match to CN method.

  25. RESULTS: Calculated Annual CN Runoff vs. Gauged Discharge • We have no basis of comparing annual CN runoff estimates with the Pilot Study results. • Pilot Study only tested growing season edge-of-field CN runoff against growing season gauged discharge. • But, SCS annual runoff charts* are available, which are also CN-based. *SCS Engineering Field Manual, Notice from the SCS Nebraska State Office as a Supplement to the Standard Field Manual.

  26. SCS Runoff Charts for Annual Runoff Estimates Provide annual runoff estimates in inches everywhere across Nebraska as function of watershed CN and chance (%) of annual rainfall amount (50% chance = normal year)

  27. Isogram 2.5 Isogram 3.0 Annual Runoff, ac-in/ac 10% 50% Chance Of Occurrence 80% 70 CN SCS Engineering Field Manual Wood River ~ Isogram 2.5

  28. Check 1964-70 Runoff by SCS Runoff Charts - Riverdale Normal Year (1968) Data (50 % Chance Curve) 23.22” (NOAA) 24.39” (105 % of Avg.) 0.26 inches * 0.148” (57 % of Gauged) 0.257” (99 % of Gauged) 0.460” ( 177% of Gauged) “on the nose” if CN = 70 • Average Annual precip: • 1968 Kear/Ocon precip: • Gauged D.R. all of 1968: • Chart Runoff if CN = 65: • Chart Runoff if CN = 70: • Chart Runoff if CN = 75: • Conclusion: SCS chart is *Note: 1968 Growing Season Discharge was 0.18” (of 14.5” total precip) and the Average 1964-1970 Growing Season Discharge was 0.22” (of 14.8”)

  29. Wettest Year 1964-1970 Runoff by SCS Runoff Charts - Riverdale Wettest Year - 1965 Data (10 % Chance Curve) 23.22” (NOAA) 35.06” (151 % of Avg.) 1.01” 1.100” (109 % of Gauge) 1.520” (150 % of Gauge) 2.200” (218 % of Gauge) “on the nose” if CN = 64 • Average Annual precip: • 1965 Kear/Ocon precip: • Gauged D.R. 1965: • Chart Runoff CN = 65: • Chart Runoff CN = 70: • Chart Runoff CN = 75: • Conclusion SCS chart is :

  30. Driest Year 1964-1970 Runoff by SCS Runoff Charts - Riverdale Driest Year - 1970 Data (80 % Chance Curve) 23.22” (NOAA) 18.52” (80 % of Avg.) 0.12” 0.046” (39 % of Gauge) 0.090” (77 % of Gauge) 0.175” (149% of Gauge) “on the Nose” if CN = 72 • Average Annual precip: • 1970 Kear/Ocon precip: • Gauged D.R. 1970: • Chart Runoff CN = 65: • Chart Runoff CN = 70: • Chart Runoff CN = 75: • Conclusion SCS chart is :

  31. GROWING SEASON RUNOFF COMPARED TO ANNUAL Make Sense?

  32. RIVERDALE* SUBWATERSHED RESULTS OF CN MODEL • Annual (Only by SCS Charts) • Growing Season • Monthly • By “Identifiable” Event *Comparison of CN results with gauged flows is considered better at Riverdale vs. Alda because elevations suggest there is no base flow at Riverdale.

  33. Monthly and Growing Season CN Model Results (Test 1 - w/Irrig)CN Model as Percent of Gauged Streamflow 1964-1970, Riverdale Observations: (Note: Gauged Flow ~ Direct Runoff at Riverdale) Generally poor monthly results, some “fair.” Events cross months. Average G.S. Modeled R.O. = 5,844 af, Gauged R.O. = 6,100 af (Difference may be due to some base flow)

  34. Conclusions?

  35. Results of Tests 1 and 2Comparison of Monthly and Seasonal CN Model Results with and without Irrigation Algorithm Running at Riverdale Observations: (Note: Gauged Flow was 42,700 af) Moderately variable by year; both models had EOF runoff for most months < gauged, suggesting possible base flow in gauged amounts. If there is no base flow, Test 1 over all 7 years is within 4 % of gauged flow.

  36. Tests 1 and 2“BEST” Years1965, 1967

  37. Tests 1 and 2“WORST” Years1964, 1969

  38. Tests 1 and 2“WORST” Years1964, 1969 1969 AMC I Problem 1964 AMC III Problem

  39. Example AMC III Problem - Riverdale

  40. Example AMC III Problem - Alda

  41. Partial AMC III Problem

  42. CONCLUSIONSRiverdale Watershed Runs • SCS annual charts surprisingly accurate • CN model edge-of-field runoff generally < gauged flow, suggesting base flow in gauged amounts • Matching by month N.A. due to overlapping events • CN model gives very good match by individual “identifiable” events (well within ranges in literature) • Runs w/o irrigation probably better because algorithm introduces additional AMC III problems, and NRCS CNs mostly derived in “humid” areas

  43. STUDY RESULTS Alda Watershed • Annual Comparisons of Modeled with Gauged Values • Totals During all 7 Growing Seasons • By Individual Growing Seasons • Monthly • By each Set of “Identifiable” Events • By Individual “Identifiable” Events *Comparison of CN results with gauged flows is considered better at Riverdale vs. Alda because there is ‘no’ base flow evident at Riverdale, and the WHAT method appears to overstate long-term base flows.

  44. ANNUAL RESULTS AT ALDA • SCS Annual Runoff Charts could not be tested at Alda because of the uncertainty in the long-term WHAT estimates of direct runoff • However, as noted below, the WHAT method appears to give reasonable values for “identifiable” events

  45. Compare Tests 3 and 4Comparison of Monthly and Seasonal CN Model Results with Irrigated Lands Irrigated versus Dryland at Alda Observations: (Note: Total 7-season Gauged Flow was 62,384 af) *Significant number of AMC III problems occur in both models. Both models had G.S. EOF runoff for all seasons > gauged; intuitive with base flow and transit losses?

  46. Comparisons of Average Growing Season RUNOFF Tests 1-4, 1964-1970 Riverdale and Alda, ac-ft Avg G.S. Gauged Flow at Riverdale: Avg G.S. Gauged Flow at Alda: Test 1. Riverdale w/irrig: 2. Riverdale w.o./irrig: 3. Alda w/irrig: 4. Alda w.o./irrig: • 4,348 ac-ft • 8,912 ac-ft • 5,260 121% • 5,054 116% • 16,961 190% • 16,027 180% CN Model Results a.f.% Gauged (Edge-of-field) Observations: CN model w or w.o./irrig closely predicts average seasonal outflows at Riverdale, suggests EOF runoff at Alda is ~ 185% of gauged

  47. Test 5 - CN Growing Season and Monthly Results at AldaRunoff Model w/Irrig Algorithm Running as Percent of Gauged Streamflow 1999-2005 Observations: 1999-2005 Results for Alda had many AMC I, III Problems Generally poor monthly results, numerous over-end-of-month events. Unlike ‘64-’70 G.S. results, many months and G.S.s had EOF runoff < gauged. Does (can?) difference for those cases = base flow minus transit losses?

  48. Test 6 - CN Growing Season and Monthly Results at AldaRunoff Model W.O./Irrig Algorithm Running as Percent of Gauged Streamflow 1999-2005 Observations: Many months & G.S.s had EOF runoff < gauged (base flow minus losses?) But 7-yr Average G.S. Modeled = 3,296 af, Gauged = 3,518 af (close) 7-yr Average G.S. Modeled if Exclude 2004 = 3,969 af

  49. Cn MODEL Results for 6 “Identifiable” runoff-rainfall Events at alda for 1964 to 1970

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