Simulation and Evaluation of Surface Irrigation Systems Using WinSRFR’s Simulation Engine

1. Simulation and Evaluation of Surface Irrigation Systems Using WinSRFR’s Simulation Engine Eduardo Bautista and Albert J. Clemmens Presentation to Arizona NRCS November 2007

2. Training Session Objectives • Familiarize participants with the Simulation component of the WinSRFR program • Suggest a strategy for using WinSRFR when evaluating EQIP proposals

3. Presentation Outline • Fundamental concepts in surface irrigation analysis • Hydraulics • Performance concepts and indicators • WinSRFR • Program functionalities (Worlds) • Data organization • Conducting a simulation analysis in WinSRFR • Inputs • Outputs

4. Presentation Outline (Continued) • Analyzing an EQIP proposal • Establishing current conditions: data requirements • Analyzing operational and design alternatives • Sensitivity/reliability of results • Examples

5. Fundamental Concepts Hydraulics

6. Surface irrigation hydraulics • Surface irrigation is an example of unsteady open-channel flow (flow changes with time and distance).We use the 1-D equations of unsteady open channel flow to model this process

7. Conservation of mass (Volume balance) • Applied Volume (Vin) is equal to the sum of volume of surface storage (Vy), infiltrated volume (Vz) and runoff volume (Vro) • WinSRFR calculates infiltration using empirical equations (e.g NRCS infiltration families)

8. Conservation of momentum • Derives from F = ma, flow acceleration is the result of forces acting on the mass of water • Main forces are pressure gradient, the weight component in the direction of flow, and hydraulic drag (friction slope) • The empirical Manning formula is used to calculate hydraulic drag Friction slope Weight Pressure gradient

9. Surface irrigation simulation model • Computational solution of the governing equations • The solution predicts the evolution of surface flow depths, surface discharge, and infiltrated depths as a function of space and time

10. Important model limitations • WinSRFR assumes one-dimensional flow • not applicable to situations where the flow is affected significantly by cross-slope • Difficulties in modeling irregularly shaped fields

11. Models available in WinSRFR • Zero-inertia(equilibrium model) • Kinematic-wave (normal depth model)

12. Accuracy of WinSRFR results • Depends on: • differences between the model and the actual physical system (as explained in limitations) • Uncertainty in modeling infiltration and hydraulic resistance processes • the accuracy of inputs (GARBAGE IN = GARBAGE OUT)

13. Fundamental Concepts Performance concepts and indicators

14. Ultimate water distribution and irrigation performance measures lq L

15. Application efficiency

16. Low-quarter distribution uniformity

17. Adequacy of the low-quarter

18. Potential application efficiency

19. Important! Application efficiency ≠ Irrigation efficiency • Application efficiency is a measure of hydraulic performance, measured relative to a defined application target • Irrigation efficiency is a measure of beneficial uses of water (and thus of management performance). Its calculation considers • All beneficial uses (e.g., ET, leaching) • Ultimate water destinations (water in storage, return flows) • Events over seasonal or longer time frames • Water budgets over regions with well-defined boundaries

20. The WinSRFR Software Functionalities and data organization

21. WinSRFR 2 1 3

22. Field geometry Length Cross section Bottom description (slope or elevations) Management variables Inflow as a function of time Downstream boundary condition Observed outputs Advance/recession Runoff Water penetration profile Performance measures Application efficiency (AE) Distribution uniformity (DU) Adequacy (AD) Runoff and deep percolation fractions (RO% and DP %) Infiltration parameters (resistance parameters in future versions) Evaluation Given Find

23. Field geometry Length Cross section Bottom description (slope or elevations) Soil and crop hydraulic properties Infiltration Hydraulic resistance Management variables Inflow as a function of time Downstream boundary condition Evolution of surface and subsurface flows Q(x,t) A(x,t) Z(x,t) Performance measures Application efficiency (AE) Distribution uniformity (DU) Adequacy (AD) Runoff and deep percolation fractions (RO% and DP %) Simulation Given Find

24. Field geometry Cross section Slope or bottom elevation Soil and crop hydraulic properties Infiltration Hydraulic resistance Management variables Available flow rate Downstream boundary condition Field dimensions (length, border width/furrow set width) that will attain feasible and practical levels of performance Design tools Given Find

25. Field geometry Cross section Slope or bottom elevation Field dimensions Soil and crop hydraulic properties Infiltration Hydraulic resistance Management variables Downstream boundary condition Unit discharge and cutoff time (or location) combination(s) that will attain feasible and practical levels of performance Operational analysis Given Find

26. Why are we not providing training in the use of the operational and design analysis tools? • WinSRFR 1.2 has been approved by NRCS but complete design/operations tools are available for graded open-ended bordersonly • WinSRFR 2.1 will have tools for borders, basins, and furrows, but will not be released until the end of November (at earliest)

27. The analysis explorer and data organization • Hierarchical data structure, allows organizing related scenarios • Data exchange using copy and paste

28. Conducting a Simulation analysis in WinSRFR

29. 1) Creating a new Simulation scenario Right-click (pop-up menu)

30. 2) Defining the system type and downstream boundary conditons (border example) • In simulation, border = basin

31. 3) Defining the system geometry • Length –width • Berm height (overtop height) • Changing input units

32. 3) Defining the system geometry • Options for describing the bottom elevation • Constant slope • Modified slope • Elevation table • Calculated slopes** (needed when specified elevations/slopes cause computational problems) • Copy-and-paste from Excel

33. 4) Defining the system’s roughness characteristics • NRCS suggested Manning n values • User entered values • Ignore other options (for advanced users)

34. 5) Defining the system’s infiltration characteristics - Options • NRCS Infiltration Families • Characteristic infiltration time • Time Rated Infiltration Families • Kostiakov formula • Extended Kostiakov formula • Branch function

35. 5) Defining the system’s infiltration characteristics - Assumptions • Empirical formulations, assume one-dimensional flow and infiltration as a function of opportunity time only • Analysis assumes “average” infiltration properties for the field τ Z=f(τ, k,a,..)

36. 5) Defining the system’s infiltration characteristics – NRCS Families (NRCS, 1997. National Irrigation Guide)

37. 5) Defining the system’s infiltration characteristics – Characteristic infiltration time • Characteristic depth can be • Required depth • Typical application depth • Requires reasonable estimate of a • 0.6 or greater for lighter soils • 0.4 or less for tight soils • Not a good choice for cracking soils

38. Accuracy of infiltration functions and sensitivity of simulation results to infiltration estimates

39. 6) Defining the inflow hydrograph • Standard and tabular options • Cutoff options • Time-based • Distance-based • Cutback options • Time-based • Distance-based

40. 7) The Data Summary tab • Allows quick changes of some variable/ parameter values but not of analysis options • Cannot select a new NRCS family

41. 8) Execution • Simulation model • Default user execution options • For many applications, adequate • Errors and warnings

42. The animation window

43. Modifications for furrows • Geometry • Infiltration • Inflow

44. Geometry options • Trapezoid • Parabola (power law)

45. Defining furrow geometry ss b0

46. Estimating furrow geometry from field data

47. Modifications for furrows-infiltration • Calculation of furrow infiltration using the NRCS approach (SCS, 1984, NEH, Section 15, Chapter 5)

48. Limitations of the NRCS approach • Empirical WP calculations results in systematic errors under some conditions • Uses another empirical formula to calculate hydraulic gradient and WP under zero slope • Estimates are best under steep slope conditions (where the kinematic wave model is applicable) • Bugs discovered in SRFR engine, to be corrected in WinSRFR V2.1 • Other improvements target for V3

49. Modifications for furrows-inflow • Inflow specified on a per furrow basis (V 1.2)

50. Simulation outputs