Return Flows Discussion Continued ESHMC Meeting 6 May 2008 Stacey Taylor

Return Flows Discussion Continued

ESHMC Meeting6 May 2008

Stacey Taylor

Why Return Flows are Important

Snake

River

Diversion

Return

FieldField

Field

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 Component Reach-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 period Shorter period

Questions to Answer at the ENDCurrent status:– Returns = 0 + b1*Div (Recharge tool); where b1 = ∑ (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:RMay = 0.05 * 100RJune = 0.05 * 200 + 0.03 * 100RJuly = 0.05 * 300 + 0.03 * 200 + 0.02 * 100

1 2 3 4 5 6 7 8 9 10 11 12

0.05 0.03 0.02 0 0 0 0 0 0 0 0 0Lag Coeff:

May Jun Jul

100 200 300Div:

Month 1

Month 2

Month 3

∑ (lag coefficients) = 0.05 + 0.03 + 0.02 = 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 = b1 * Diversions Returns= -bo+b1*Diversions) Returns = exponential fct

The Last Meeting on 3/6/2008 (cont)

(2) Ongoing Snake River return data• “Group” data for 2002-2006• 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)

19771961



SLOPEShared range: 0.014 to 0.023 (excludes p>10%)

Average value: 0.019 (excludes p>10%)

Y-INTERCEPTShared range: -4.5 to -4.0 (excludes p>10%)

Average value: -4.25 (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-ftX = diversion in 1000 ac-ft

Average intercept value

Richfield Entity (IESW054)




SLOPEShared range: 0.17 to 0.21 (excludes p>10%)

Average value: 0.19 (excludes p>10%)

Y-INTERCEPTShared range: -9.8 to -2.8 (excludes p>10%)

Average value: -6.3 (excludes p>10%)

P>>10%

P>>10%

P>10%


• Proposed equation to use in the recharge tool for this entity:

y = 0.19x - 6.3

• 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 1928-1950)

Average slope

Average intercept

where:y = return in 1000 ac-ftx = 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 2002-2006• 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


2000s

1980s


2000s

1980s


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 Today1. 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)

Documents

Return Flows Discussion Continued ESHMC Meeting 6 May 2008 Stacey Taylor