Return Flows Discussion Continued ESHMC Meeting 6 May 2008 Stacey Taylor

Why Return Flows are Important Snake River Diversion Return Field end of canal Wet lands

Return Flows 101 Return flow - irrigation water returning to the surface water system (includes end of canal spills and surface run-off) Irrigation diversions deplete and affect timing of flows in the river where some of diverted water returns to the river as surface or ground water return flows

Importance of Return Flows in ESPAM1 Along with ET, canal seepage, pumping, and crop mix, return flows are used to estimate aquifer recharge and discharge associated with irrigation. Field Delivery = Diversions - Canal Leakage - Return Flows Net Recharge (surface) = (Field Delivery + Precipitation) – (ET x Adjustment Factor) For some entities, return flows are as big of a part of the water budget as ET

Reach Gain/Loss Program (RGLP) Water Budget ComponentReach-Gain Targets Diversion – Return – ET – Canal Leakage Downstream gage + Diversions – Tributary Inflows – Returns Diversions: from IDWR data files Diversion x lag factors (applied month-by-month) Return = Div x ∑(lag factors) 6 month periodShorter period

Questions to Answer at the END Current status: – Returns = 0 + b 1 *Div (Recharge tool); where b 1 = ∑ (RGLP lags) – Reach-Gain/Loss Program: 1.Do we change the above equation for recharge? 2.Do we change coefficients year-to-year? 3.If “YES” to previous question, do we rebuild the RGLP? Month: Lag Coefficient:

Sample Calculations for Returns in RGLP Returns: R May = 0.05 * 100 R June = 0.05 * * 100 R July = 0.05 * * * Lag Coeff: MayJunJul Div: Month 1 Month 2 Month 3 ∑ (lag coefficients) = = 0.10  Goes into water budget

The Last Meeting on 3/6/2008 (1) Historical records of Big Wood and Richfield Calculation methods Rasters Plots of returns vs. diversions Returns = b 1 * Diversions Returns= -b o +b 1 *Diversions) Returns = exponential fct

The Last Meeting on 3/6/2008 (cont) (2) Ongoing Snake River return data “Group” data for Plotted returns vs. diversions Plotted returns vs. normalized diversion New idea from the March meeting: Plot indexed returns vs. normalized diversion

Big Wood Entity (IESW007)

Big Wood Entity (IESW007)

SLOPE Shared range: to (excludes p>10%) Average value: (excludes p>10%) Y-INTERCEPT Shared range: -4.5 to -4.0 (excludes p>10%) Average value: (excludes p>10%) P>>10%

Big Wood Entity (IESW007) Proposed equation to use in the recharge tool for this entity: y = 0.019x – 4.25 Assumed negative intercept because average y-intercept value is significant over the scale of plot returns vs. diversions. Average slope value where: y = return in 1000 ac-ft X = diversion in 1000 ac-ft Average intercept value

Richfield Entity (IESW054)

SLOPE Shared range: 0.17 to 0.21 (excludes p>10%) Average value: 0.19 (excludes p>10%) Y-INTERCEPT Shared range: -9.8 to -2.8 (excludes p>10%) Average value: -6.3 (excludes p>10%) P>>10% P>10%

Richfield Entity (IESW054) Proposed equation to use in the recharge tool for this entity: y = 0.19x Assumed negative intercept instead of zero intercept since this value (-6.3) is relatively significant over the scale in the plot of returns vs. diversions (excluding abnormal points in the years ) Average slope Average intercept where: y = return in 1000 ac-ft x = diversion in 1000 ac-ft

Conclusion on the Historical Data The Big Wood entity and the Richfield entity may agree on a similar form of an equation (linear line with negative intercept)

Ongoing Snake River Return Data Involves “group” data for At the last meeting, very few data points were available to determine an equation Incorporated more data points using 80s data provided by Dick Lutz for groups 3, 4, 5 and 1/11 Goal: determine general equation from the returns/diversions for the recharge tool

Notice Scale on X-axis (0.5 to 1 to show points better)

Appears to be no general trend between the 80s and 2000s OR is there just not enough data to tell??

Note different X and Y scales

2000s 1980s Note different X and Y scales

2000s 1980s Note different X and Y scales

2000s 1980s Note different X and Y scales

Conclusion on “Groups” Data Few data points for the “groups” (recent data) do not allow for a distinct equation to compare to the historical data.

Questions to Answer Today 1.Do we change the equation for recharge calculations? – YES, because a better equation may fit the lines – NO, because then there’s consistency with the RGLP 2.Do we change coefficients year-to-year? – YES, because the change in slopes between years we see must be real so we must change them. – NO, because we don’t have enough data to know 3.If “YES” to previous question, do we rebuild the RGLP? – YES, because it may be better in the long run – NO, because we can just run the RGLP in 3 sections (80s, 2000s, 2007)