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FINAL REPORT (Updated 02/16/2010 with Footnotes)

FINAL REPORT (Updated 02/16/2010 with Footnotes). COHYST Pilot Project Wood River Watershed Surface Runoff Model COHYST Technical Committee Final Report with Footnotes. TWO VERSIONS. Two versions of this presentation are available: Tech Committee version – this one.

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FINAL REPORT (Updated 02/16/2010 with Footnotes)

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  1. FINAL REPORT (Updated 02/16/2010 with Footnotes) COHYSTPilot ProjectWood River WatershedSurface Runoff ModelCOHYST Technical Committee Final Reportwith Footnotes

  2. TWO VERSIONS • Two versions of this presentation are available: • Tech Committee version – this one. • Sponsor’s version – less detailed. • This Tech Committee version has greater detail with footnotes, and constitutes the final report for this project.

  3. Review - July 12, 2007 Proposal to SponsorsSurface Water Model Options • Annual CN Model – Develop a model to estimate land use impacts on surface runoff on an annual basis using annual rainfall and composite CNs for subareas of the test watershed ($5K) . • Monthly CN Model – Develop a model to estimate land use impacts on surface runoff on a month-by-month basis using monthly rainfall and composite CNs for subareas of the test watershed ($10K). • Weekly CN Model – Develop a model to estimate land use impacts on surface runoff on an annual, monthly, and week-by-week basis using weekly rainfall and spatially-varied, GIS-distributed CNs to determine field runoff ($25K). • Daily CN Model – Develop a model to estimate land use impacts on surface runoff on a daily basis using time-varied, GIS-distributed CNs to calculate daily values of field runoff, then route the field runoff to the river using time of travel methods ($100K). No. 3 was approved, but actual effort was ~ 90% of No. 4

  4. PILOT STUDY OBJECTIVES • Develop and perform a pilot test of a spatially-distributed, CN-based weekly daily rainfall-runoff model for the COHYST area that can predict the short and long-term impacts of land use changes on runoff from rainfall. • Evaluate whether the CN method can be used to reveal anything about the validity of the recharge “bump” used in the COHYST models.

  5. PILOT STUDY OBJECTIVES • Compare CN Model estimates of field-level runoff with WHAT estimates of direct surface runoff at the gauges (not a definitive study of WHAT). • Recommend how the CN method can best be applied in future COHYST (and Conjunctive Management) work.

  6. IS “CN” AN ACCEPTED TOOL FOR predicting impacts of land use changes? ASCE Task Force, “Curve Number Hydrology, State of the Practice,” 2009, p. 73: “Applying the CN technology to determine land use influences on hydrology should be encouraged.”

  7. “Primer” SCS CN Method Decreasing CN CN = 90 Smaller CNs give less runoff for the same rain amount CN = 70

  8. CN TABLE Effect on CN (and runoff) of converting from row crops to small grain crops to meadows to pasture Direction of decreasing CN and decreasing runoff for same rain

  9. EXAMPLES – EFFECTS OF CN ON RUNOFF FOR SAME RAIN AMOUNT AMC = “Antecedent Moisture Condition”: I = dry, II = normal, III = wet

  10. 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, G.L., J.B., R.V., R.K. • Selected two 7-yr Growing Season 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.

  11. HANDOUTS • Inventory of Key Spreadsheets and Contents • Original Scope of Work • Descriptions of Six “Tests” with Commentary • Copies of Slides • AllAvailable on the ftp Site All posted on ftp site under “Wood River Pilot Study/New Folder”

  12. PROCEDURE PILOT TEST OF CN-METHOD • Determine total daily edge-of-field runoff from the area above two stream gauges by CN method during two 7-yr test periods for (a) individual runoff events, (b) monthly runoff, (c) growing season runoff, and (d) annual runoff. • Identical to method used in Cropsim • Determine the gauged amount of streamflow from USGS discharges for the same periods. • Compare and interpret differences between Nos. 1 and 2. • What could the differences in Nos.1&2 represent?

  13. Model CellsRiverdale and Alda GaugesRiverdale 58% of Total Area above Alda 163,186 ac 221,737 ac

  14. CN MODEL 2001* CALMIT LAND USE CLASSIFICATIONS

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

  16. “IDENTIFIABLE” RUNOFF-RAINFALL EVENTS • Definition: • Stand-alone direct runoff hydrograph with 1- to 10-day rain, and no apparent AMC I, III “Problem” * • How Found (21 years of daily flows): • Use WHAT estimates to identify beginning and ending dates of direct runoff hydrographs. • Examine daily precipitation to assess dates and amounts of rainfall that produced each hydrograph. • Determine CN model estimates for runoff on each day of rain that produced the hydrograph. *The “AMC I, III Problem” is described in more detail later.

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

  18. “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.”

  19. ALGORITHM DEFININTIONS Two algorithms were used for CN modeling, and assessments of each are described later: • AMC I, II, III Algorithm • This is a built-in part of the SCS CN Method, also used in CROPSIM • Irrigation Algorithm for Irrigated Crops • This was added by the Technical Committee

  20. AMC I, II, III 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 *Growing season algorithm used in both Cropsim and COHYST, dormant season rainfall amounts also available from NRCS.

  21. PARTIAL AMC I, II, III CONVERSION TABLE These are discrete steps, not uniformly distributed.

  22. 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

  23. LITERATURE ON AMC I, II, III METHOD • Data for published tables “cannot be found.” • AMC classes I, II, III “discouraged” by NRCS in 1993 but admit that “application is widespread.” • 2008 NRCS recommended ARC I, II, III Curves based on frequencies of runoff events. • 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.

  24. “IRRIGATION ALGORITHM” The edge-of-field runoff for both the Riverdale and Alda watersheds was modeled for both 7-year periods with and without the “irrigation algorithm” running. Because the CN method doesn’t distinguish between irrigated crops and dryland, this algorithm was created by the Technical Committee in order to evaluate runoff for irrigated crops. The algorithm adds 1” of water in 3 days whenever a 4-day rainless period precedes “today.” This caused the CN method to recognize that the soil would be “wetter” if the crop was irrigated, increasing the CN from I to II, or II to III depending on the 5-day amounts. (Note: Tests with this showed that about 10 applications of irrigation water would occur during the growing season)

  25. “DETAILS OF 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)

  26. 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)

  27. SUMMARY OF FINDINGSWith and Without Irrigation Algorithm • RIVERDALE SUBWATERSHED, 1964-1970 (Tests 1 & 2) • ALDA WATERSHED, 1964-1970 (Tests 3 & 4) • ALDA WATERSHED, 1999-2005 (Tests 5 & 6, and 6a and 6b)

  28. Riverdale Subwatershed RESULTS • Compare CN-Based Annual Estimates of Direct Runoff to Gauged Flows and WHAT D.R. Values at Riverdale • By Individual “Identifiable” Events • By “Identifiable” Events as a Group • Monthly • Growing Season • Annual • Is there base flow at Riverdale?

  29. 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.

  30. IS THERE BASE FLOW AT RIVERDALE? Distance, miles above Alda Gauge

  31. RIVERDALE RESULTS: “IDENTIFIABLE” EVENTS35 Events, 1964-1970 Growing Season

  32. 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)

  33. Riverdale ResultsMonthly, Tests 1 and 2 “BEST” Years 1965, 1967

  34. Riverdale ResultsMonthly, Tests 1 and 2 “WORST” Years 1964, 1969

  35. Example AMC III Problem - Riverdale

  36. Example AMC III Problem - Alda

  37. Growing season Results of Tests 1 and 2Comparison of Growing Season CN Model Results with and without Irrigation Algorithm Running at Riverdale Observations: Gauged Flow was 42,700 af (0.193”), Total Precip was 99.46” Moderately variable by year; both models had EOF runoff for most months < gauged, suggesting possible base flow in gauged amounts. WHAT direct runoff at gauge = 30,407 af (71 percent of gauged flow), suggesting “loss” of 10,504 af (0.05”)

  38. RIVERDALE ANNUAL RESULTSCN Runoff vs. Gauged Discharge • 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, EFM Notice NB-26, 4/81.

  39. 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)

  40. 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

  41. 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 Flow CY 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 0.26” total gauged)

  42. 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 :

  43. 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 :

  44. GROWING SEASON RUNOFF COMPARED TO ANNUAL Reasonable?

  45. FINDINGS: BASEFLOW QUESTION RIVERDALE GAUGE, TESTS 1&2 • Total gauged flow for entire 1964-1970 growing seasons = 42,700 af • CN model with irrigation estimated edge-of-field runoff = 40,911 af (96% of Gauged) • WHAT method direct runoff at gauge = 30,407 af (71% of Gauged) Observations: Even with the data on elevations, the fact that EOF < Gauge suggests there may be “base flow” at Riverdale; saw earlier that for single runoff-rainfall events, WHAT method runoff at gauge reasonably agrees with CN method EOF runoff.

  46. CONCLUSIONSRiverdale Watershed (Tests 1 & 2) • SCS annual charts are surprisingly accurate. • Gauged, WHAT, & CN runoff are < 2.3% of 99” rain. • CN model with irrigation algorithm estimates growing season runoff as 96% of gauged flow. • Because CN model edge-of-field runoff < gauged flow, suggests there is some base flow in the gauged amounts. • WHAT predicts that 71% of the gauged is direct runoff; CN predicts that 96% of gauged is available at EOF, so these are not out of line.

  47. ALDA WATERSHED RESULTS Paired Runs 3-4; 5-6; 6a-6b 1964-1970 Growing Seasons 1999-2005 Growing Seasons By individual “Identifiable” Events By “Identifiable” Events as a group Monthly Growing Season Annual

  48. Cn MODEL Results for 15 “Identifiable” runoff-rainfall Events at alda for 1999 to 2005 EVENTS AS A GROUP Model Runoff w/irrig, Percent of Gauged: 50% Model Runoff w0/irrig, Percent of Gauged: 37% WHAT Runoff, Percent of Gauged: 48%

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

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