Simulation and Evaluation of Surface Irrigation Systems Using WinSRFR’s

Simulation Engine

Eduardo Bautista and Albert J. Clemmens

Presentation to Arizona NRCS November 2007

Training Session Objectives

Familiarize participants with the Simulation component of the WinSRFR program

Suggest a strategy for using WinSRFR when evaluating EQIP proposals

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

Presentation Outline (Continued)

Analyzing an EQIP proposal– Establishing current conditions: data requirements– Analyzing operational and design alternatives– Sensitivity/reliability of results

Examples

Fundamental Concepts

Hydraulics

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

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)

ROZYin VVVV

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

fSSx

y

0

Weight

Friction slope

Pressure gradient

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

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

Models available in WinSRFR

Zero-inertia(equilibrium model)

Kinematic-wave (normal depth model)

fSSx

y

0

fSS 0

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)

Fundamental Concepts

Performance concepts and indicators

Ultimate water distribution and irrigation performance measures

X

D

DappDinf

DreqDrz

Dlq

Ddp

DroDreq = soil water deficit + leaching requirement

Llq

Application efficiency

100(%) app

rz

D

DAE

X

D

DappDinf

DreqDrz

Dlq

Ddp

DroDreq = soil water deficit + leaching requirement

Low-quarter distribution uniformity

infD

DDU lq

lq X

D

DappDinf

DreqDrz

Dlq

Ddp

DroDreq = soil water deficit + leaching requirement

Adequacy of the low-quarter

req

lqlq D

DAD

X

D

DappDinf

DreqDrz

Dlq

Ddp

DroDreq = soil water deficit + leaching requirement

Potential application efficiency

)%100(

)(

lossessurfaceDU

DDD

DPAE

lq

reqlqapp

rzlq

X

D

DappDinf

DreqDrz

Dlq

DdpDro

Dlq=Dreq

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

The WinSRFR Software

Functionalities and data organization

WinSRFR

12

3

Evaluation

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)

Given Find

Simulation

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 %)

Given Find

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

Operational analysis

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

Given Find

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)

The analysis explorer and data organization

Hierarchical data structure, allows organizing related scenarios

Data exchange using copy and paste

Conducting a Simulation analysis in WinSRFR

1) Creating a new Simulation scenario

Right-click (pop-up menu)

2) Defining the system type and downstream boundary conditons (border example)

In simulation, border = basin

3) Defining the system geometry

Length –width Berm height (overtop height) Changing input units

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

4) Defining the system’s roughness characteristics

NRCS suggested Manning n values

User entered values Ignore other options

(for advanced users)

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

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,..)

5) Defining the system’s infiltration characteristics – NRCS Families

(NRCS, 1997. National Irrigation Guide)

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

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

6) Defining the inflow hydrograph

Standard and tabular options

Cutoff options– Time-based– Distance-based

Cutback options– Time-based– Distance-based

7) The Data Summary tab

Allows quick changes of some variable/ parameter values but not of analysis options

Cannot select a new NRCS family

8) Execution

Simulation model Default user execution

options – For many applications,

adequate

Errors and warnings

The animation window

Modifications for furrows

Geometry Infiltration Inflow

Geometry options

Trapezoid Parabola (power law)

Defining furrow geometry

Furrow geometry

0

1

2

3

4

5

6

7

-25 -20 -15 -10 -5 0 5 10 15 20 25

x(ft)

y(ft)

5

25

125

225

325

425

525

b0

ss

mCyT

Furrow geometry

0

1

2

3

4

5

6

7

-25 -20 -15 -10 -5 0 5 10 15 20 25

x(ft)

y(ft)

5

25

125

225

325

425

525

Estimating furrow geometry from field data

Modifications for furrows-infiltration

Calculation of furrow infiltration using the NRCS approach

(SCS, 1984, NEH, Section 15, Chapter 5)

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

Modifications for furrows-inflow

Inflow specified on a per furrow basis (V 1.2)

Simulation outputs

The Scenario Comparison Tool

Graphs and underlying data can be transferred to other applications

Housekeeping – managing file size

The “File/Clear all Results” command

Analyzing a proposal

Can performance be improved with the current system? What is the potential impact of the proposed improvement?

Current conditions: Data challenges

Limited data Unreliable data Short time to complete the assignment

Data requirements

Data spreadsheet “Hard” data “Soft” data and measures of error Validation data

Hard data

System typeborder/basinfurrow

Target application depthDepth value

Downstream boundary condtionOpenClosed

DimensionsLengthWidthTrapezoidal field

minimum lengthmaximum length

Border geometryBorder widthFurrow guides?Other?

Furrow geometrySpacingFurrows/setDepthBottom widthTop width

Bottom slopeSlope valueUniformity

Cross slopeSlope value

Soft data

RoughnessCropSurface conditioning

InfiltrationSoil taxonomic description orSoil texture orInfiltration family orTime to infiltrate target application depth (preferred)

Hard/soft data

Inflow ManagementWater sourceDischarge valueIf discharge is not constant between irrigation events

Discharge minDischarge max

Cutoff criteriaIf time, typical set timeIf distance, typical cutoff distanceIf ponding time (Upstream or downstream), typical time

Runoff recovery (open ended systems)On farm recoveryOff-farm recoveryPercent recovered

Validation measures

Performance variablesAdvance time to the end of the field (Typical, max, min)Recession time (time needed for water to disappear after cutoff)Typical upstream depth of flowPuddle areas?Maximum outflow rate (as percent of inflow)Labor use (acres/irrigator)

What can go wrong?

Incorrect or non-uniform field slope Incorrect inflow rate

– Is the flow measured?– Is the flow measurement method reliable?

Downstream boundary condition Infiltration/roughness Computational issues

Example

Analyzing a proposal

Operational and Design Alternatives

Assess Potential Application Efficiency with Current Design: Graded Basin GC3-01-05

Find an alternative operational strategy (Q-tco)

Based on field dimensions (L * W), required depth (Zreq), and PAE, compute required application volume (Vapp)

Divide Vapp by a reasonable inflow rate (Q) to obtain a set time (tco) or…

Divide Vapp by a reasonable set time (tco) to obtain an inflow rate (Q)

Test strategy with simulation

Example: calculate adjusted Q/tco

Adjusted inflow for Example GC-3-01-05: simulation results

Sensitivity analysis

Objective is to assess the impact on performance of likely variations in design inputs from actual field conditions

In general, a well-designed and managed system will tolerate some variations in inputs, with a well-defined management strategy (time-based or distance-based cutoff)

Performance of suggested operation

Improved system– PAEmin = 81.6 % – PAElq = 90.8 % – AE = 82.3 % – DUmin = 0.82 – DUlq = 0.915 – ADmin = 0.991 – ADlq = 1.106

Original system– AE = 61.7 %– ADlq = 1.00– DUmin = 0.61– DUlq = 0.61– RO = 0.00%– DP = 38.3%

Testing the effect of infiltration

Infiltration families or characteristic time are useful concepts for testing the sensitivity of our solution to infiltration

Faster infiltration

Slower infiltration

Sensitivity of results based on recommended Q (10 cfs) and tco (39 min)

Still getting good infiltration distribution when infiltration rate is faster than assumed in the analysis…

… but we will underirrigate the upper part of the field if infiltration is substantially slower than assumed.

AE = 77.2 % DUmin = 0.638DUlq = 0.707 ADmin = 0.771ADlq = 0.855

AE = 82.3 % DUmin = 0.787DUlq = 0.89 ADmin = 0.951 ADlq = 1.075