a Water Management - United States Bureau of Reclamation€¦ · Figure 26: SID total annual...

Development of a Daily Water Management Model of the Lower Umatilla River Basin, Oregon, using RiverWare

U.S. Department of the Interior Bureau of Reclamation Pacific Northwest Region Pacific Northwest Regional Office Boise, Idaho

U.S. Department of the Interior

The U.S. Department of the Interior protects America’s natural resources and heritage, honors our cultures and tribal communities, and supplies the energy to power our future.

Bureau of Reclamation

The mission of the Bureau of Reclamation is to manage, develop, and protect water and related resources in an environmentally and economically sound manner in the interest of the American public.

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Development of a Daily Water Management Model of the Lower Umatilla River Basin, Oregon, using RiverWare

U.S. Department of the Interior Bureau of Reclamation Pacific Northwest Region Pacific Northwest Regional Office Boise, Idaho

November 2020

Table of Contents

1.0 Introduction .....................................................................................6

2.0 Lower Umatilla River Basin...........................................................6

3.0 RiverWare Model Development.....................................................7

3.1 Model Structure.................................................................................8

3.2 Model Inputs....................................................................................10

3.2.1

3.2.2 Reservoirs............................................................................10

3.2.3 Diversions ...........................................................................13

3.2.4 Columbia River Exchanges .................................................14

3.2.5 Water Rights .......................................................................16

3.2.6 Groundwater Response Functions ......................................16

Model Operation............................................................................18

Calibration .....................................................................................18

Reservoirs ........................................................................................18

Stream Gages ...................................................................................23

Water User Diversions and Exchanges ...........................................27

Gains and Losses .................................................................10

6.0 Model Limitations and Uncertainty ............................................36

4.0

5.0

5.1

5.2

5.3

7.0 Summary and Conclusion.............................................................36

8.0 Literature Cited .............................................................................37

Appendix A: Gains And Losses Calculations .....................................................39

Appendix B: Gains And Losses Dataset ..............................................................41

Appendix C: Live Flow and Storage Water Rights ...........................................43

List of Figures

Figure 1: Lower Umatilla River Basin and modeled reservoirs (red triangles). ........................ 7 Figure 2: Schematic of RiverWare representation of Lower Umatilla River Basin. ................. 9 Figure 3: Illustration of Cold Springs Reservoir storage capacity levels (not to scale). .......... 11

Umatilla RiverWare Development–November 2020 ii

major canals without exchanges............................................................................................... 29

Figure 4: Illustration of McKay Reservoir storage allocation and capacities (not to scale). ... 12 Figure 5: Illustration describing the return flow calculation within RiverWare Water User objects. ..................................................................................................................................... 17 Figure 6: Historical (blue) and model simulated (red) reservoir contents for McKay Reservoir. .................................................................................................................................................. 19 Figure 7: Simulated versus historical annual maximum (left) and minimum (right) reservoir contents for McKay.................................................................................................................. 19 Figure 8: Historical (blue) and model simulated (red) reservoir contents for Cold Springs Reservoir. ................................................................................................................................. 20 Figure 9: Simulated versus historical annual maximum (left) and minimum (right) reservoir contents for Cold Springs......................................................................................................... 20 Figure 10

Figure 14Figure 15annual floFigure 16Figure 17annual floFigure 18Figure 19annual floFigure 20Figure 21annual floFigure 22

: Historical (blue) and model simulated (red) outflow for McKay Reservoir. .........

: Historical (blue) and model simulated (red) flow at the YOKO. ........................... 23: Simulated versus historical irrigation season (left) and non-irrigation season (right) w volume at YOKO. ................................................................................................ 24: Historical (blue) and model simulated (red) flow at UMUO. ................................ 24: Simulated versus historical irrigation season (left) and non-irrigation season (right) w volume at the UMUO gage. ................................................................................. 25: Historical (blue) and model simulated (red) flow at UMDO. ................................ 25: Simulated versus historical irrigation season (left) and non-irrigation season (right) w volume at UMDO. ................................................................................................ 26: Historical (blue) and model simulated (red) flow UMAO. .................................... 26: Simulated versus historical irrigation season (left) and non-irrigation season (right) w volume at UMAO. ................................................................................................ 27: Historical (blue) and model simulated (red) diversions for irrigation districts and

21 Figure 11: Simulated versus historical irrigation season (left) and non-irrigation season (right) annual outflow volume from McKay. ...................................................................................... 21 Figure 12: Historical (blue) and model simulated (red) outflow for Cold Springs Reservoir. 22 Figure 13: Simulated versus historical irrigation season annual outflow volume from Cold Springs. Cold Springs does not release water during the non-irrigation season. ..................... 22

Figure 23: Historical diversions (blue), historical exchanges (green), model simulated diversions (red), and modeled exchanges (purple) for WEID. ................................................ 30 Figure 24: WEID total annual volumes for the historical canal (blue), modeled canal (green), historical pumping (red), modeled pumping (purple), historical total canal and pump total volume (orange), and modeled total canal and pump volume (black). .................................... 31 Figure 25: Historical diversions (blue), historical exchanges (green), model simulated diversions (red), and modeled exchanges (purple) for SID. .................................................... 32 Figure 26: SID total annual volumes for the historical canal (blue), modeled canal (green), historical pumping (red), modeled pumping (purple), historical total canal and pump total volume (orange), and modeled total canal and pump volume (black). .................................... 33

November 2020–Umatilla RiverWare Development iii

Table 7: Details of local gain between McKay Reservoir Umatilla River at Yoakum, OR (BirchYokoGain) calculation. .................................................................................................. 39 Table 8: Details of local gain between Umatilla River at Yoakum, OR and Umatilla River near Echo, OR (YokoUmuoGain) calculation. ................................................................................ 39 Table 9: Details of local gain between Umatilla River near Echo, OR and Umatilla River at I84 near Stanfield, OR (UmuoUmdoGain) calculation. ................................................................. 40 Table 10: Details of local gain between Umatilla River at I84 near Stanfield, OR and Umatilla River near Umatilla, OR (UmdoUmaoGain) calculation. ........................................................ 40 Table 11: Details of inflow to Cold Springs Reservoir (ColdSpringsInflow) calculation. ...... 40 Table 12: Live Flow Accounts ................................................................................................. 43 Table 13: Live Flow Storage Account ..................................................................................... 46 Table 14: Storage Accounts ..................................................................................................... 46

Figure 27: Historical diversions (blue), historical exchanges (green), model simulated diversions (red), and modeled exchanges (purple) for HID. .................................................... 34 Figure 28: HID total annual volumes for the historical canal (blue), modeled canal (green), historical pumping (red), modeled pumping (purple), historical total canal and pump total volume (orange), and modeled total canal and pump volume (black). .................................... 35 Figure 29: Local gains and losses along the Umatilla River. ................................................... 41 Figure 30: Local inflow to McKay and Cold Springs Reservoirs. ........................................... 42

List of Tables

Table 1: Maximum storage, maximum outlet capacity, and maximum spillway capacity of simulated reservoirs. ................................................................................................................ 13 Table 2: Average annual diversion for each Water User in the model. ................................... 14 Table 3: Umatilla River target flows ........................................................................................ 15 Table 4: Operational Data for Phase I and II ........................................................................... 15 Table 5: Exchange Rule parameters ......................................................................................... 15 Table 6: Details of inflow to McKay Reservoir (McKayInflow) calculation. ......................... 39

Umatilla RiverWare Development–November 2020 iv

Umatilla River at Pendleton, OR

UMUO

Acronyms and Abbreviations

Cold Springs Rechange Canal near Hermiston, OR

Hermiston Irrigation District

McKay Reservoir Outflow

National Marine Fisheries Service

Natural Resources Consulting Engineers

Oregon Water Resources Department

AF Acre‐feet

Bureau of Indian Affairs BIA

BIRO Birch Creek near Reith, OR

CSRO

HID

MCKO

NMFS

NRCE

OWRD

PDTO

POD Point of diversion

Reclamation

Columbia Exchange Canal near Hermiston, OR

Stanfield Irrigation District

Umatilla River near Umatilla, OR

Umatilla River at I84 near Stanfield, OR

Umatilla River near Echo, OR

Bureau of Reclamation

SBEO

SID

UMAO

UMDO

WEID West Extension Irrigation District

WEPO WEID Exchange Pump Plant near Hermiston, OR

WID Westland Irrigation District

YOKO Umatilla River at Yoakum, OR

November 2020–Umatilla RiverWare Development v

5

10

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1 INTRODUCTION

2 The Bureau of Reclamation uses water managenent models to assess the impacts of potential 3 adjustments to river-reservoir operations. The adjustments can be made to account for changes 4 in system infrastructure, changes in the hydrologic system, or to meet requirements for species.

This report documents the development of a daily RiverWare® ver. 8.1.1 model of the Lower 6 Umatilla River Basin. This report describes the data used in the model, the operational rules, and 7 the calibration quality of the model. 8

9

LOWER UMATILLA RIVER BASIN

The Lower Umatilla River Basin is located in central northern Oregon and covers about 550 11 square miles (Figure 1). The Basin is bounded on the east by the Blue Mountains, on the south 12 and west by the Columbia Plateau and on the north by the Columbia River. 13

The system is operated for multiple purposes including flood risk management at McKay 14 Reservoir, irrigation deliveries, and minimum flow requirements for aquatic species. Irrigated agriculture is a major economic contributor in the Basin and the majority of flow that is diverted 16 from the river is for irrigation. There are approximately 45,000 irrigated acres from Reclamation 17 Project surface water in the Basin that produce a wide range of crops including vegetables, 18 watermelon, grains, mint, alfalfa hay, pasture, and grass seed. In order to meet minimum flow 19 requirements for aquatic species, an exchange program allows water to be pumped from the Columbia River instead of the Umatilla River. 21

Water (live flow) is distributed in the system based on the rules of Prior Appropriation, where 22 the distribution priority is based on a priority date defined by when the water was first diverted 23 and put to beneficial use. Water stored in the reservoirs is delivered to diversions as requested. 24

6 Lower Umatilla River Basin RiverWare Development– November 2020

Figure 1: Lower Umatilla River Basin and modeled reservoirs (red triangles).

RIVERWARE MODEL DEVELOPMENT

A RiverWare model of the Lower Umatilla River was developed to simulate the system from

26

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30 31 McKay Reservoir to the Columba River. RiverWare is a generalized modeling tool that uses 32 logic to simulate reservoir operations and completing demands adhering to legal water right and 33 physical constraints at a daily timestep. The RiverWare model simulates the period of 1993 34 through 2019 with operating rules reflecting the last five operating years.

November 2020 – Lower Umatilla River Basin RiverWare Developement 7

35 3.1 Model Structure

36 The model network was constructed using RiverWare objects to represent physical features such 37 as reservoirs, river reaches, diversions, and river gages. Figure 2 shows the layout of the 38 RiverWare model for the Lower Umatilla River Basin. The red circles indicate water users 39 (representing diversions) and are labeled with the water user. The orange boxes indicate stream 40 gages and are named with their four-letter acronym from the Hydromet program (Reclamation

2019). The green triangles represent locations where gains and losses are input into the model. 41 The purple pentagons represent exchanges which pump water from the Columbia River in return 42 for leaving water in the Umatilla River. 43

It is important to understand that the model representation of the system is a simplification of the 44 physical system, and as such, not everything in the physical system is represented in the model. 45 In addition, the diagram is a schematic of the system and is not representative of geographic 46 distances between each object. 47

48


49

50 Figure 2: Schematic of RiverWare representation of Lower Umatilla River Basin.


55

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75

80

51 3.2 Model Inputs

52 3.2.1 Gains and Losses

53 Gains and losses are calculated for each reach in the model and are input to the model. They 54 were developed using a unregulation RiverWare model of the Basin. The unregulation model

used measured data for reservoir storage, reservoir outflow, reservoir seepage, reservoir 56 evaporation, diversion, and flow at gages to calculate gains and losses for individual reaches 57 using a simple mass balance approach. An added feature of the unregulation model was that 58 return flows from irrigation system losses were removed from the gains and losses, developing 59 gains and losses that represent a naturalized system (i.e. a system that could have existed without

irrigated agriculture or reservoir storage).

61 Equation 1 is the generalized equation that is used to calculate gains/losses to a river reach that

𝑖 𝑜 𝑔 𝑙 𝑑 𝑟 𝑒 𝑠𝑒𝑒𝑝 ∆𝑠 Equation 1

Equation 2 is the generalized equation that is used to calculate gains/losses to a river reach without a reservoir.

𝑖 𝑜 𝑔 𝑙 𝑑 𝑟 0 Equation 2

Appendix A lists the equations and the data sources that the RiverWare model used to calculate the gains and losses for each model reach.

3.2.2 Reservoirs

The Lower Umatilla River Basin has two reservoirs: Cold Springs Reservoir (off-stream near

62 contains a reservoir, where i is measured inflow, o is measured outflow, g is calculated gains, l is 63 calculated losses, d is measured diversion, r is calculated return flows, e is reservoir evaporation, 64 seep is reservoir seepage and s is the change in reservoir storage.

66 67

68

69

71 72 73 74 Hermiston, Oregon) and McKay Reservoir (located on McKay Creek before the confluence with

the Umatilla River. Cold Springs fills during the non-irrigation season with water pumped from 76 the Columbia and from the Umatilla River to provide water for the Hermiston Irrigation District 77 (HID). McKay Reservoir is operated to provide flood risk management, storage water for 78 irrigation in the Basin, and water for aquatic species in the Umatilla River. 79

Cold Springs Reservoir is an off-stream reservoir completed in 1908 by Reclamation, with a 81 capacity and active storage are 39,260 acre-feet and 38,646 acre-feet, respectively (Reclamation 82 2016c). It is an earthfill dam 115 feet high and 3,450 feet long (Reclamation 1993).


83 84 85 86 87 88 89 90

91

92

93 94 95 96 97 98 99

Water from the Umatilla River is diverted approximately 25-miles via the Feed Canal to fill Cold Springs during the non-irrigation season. This water is used during the irrigation season for HID as an exchange for water previously diverted out of the Umatilla River, which is left in-stream during the irrigation season for aquatic species. All of the discharge from Cold Springs goes into the A Line canal to supply HID with water. Figure 3 shows an illustration of the Cold Springs Reservoir, where dead and inactive storage is 614 acre-feet and active storage is 38,646 acre-feet for a total capacity of 39,260 acre-feet.

Figure 3: Illustration of Cold Springs Reservoir storage capacity levels (not to scale).

Inactive Storage 614 acre-feet

Active Storage

38,646 acre-feet Capacity

39,260 acre-feet

McKay Reservoir, located on McKay Creek, was completed in 1927 to provide flood risk management, recreation, irrigation storage, and fish and wildlife habitat and enhancements. It has an earthfill structure with a reinforced concrete paved upstream slope. McKay Reservoir has a capacity of 71,534 acre-feet with 6,000 acre-feet of that storage being exclusive space for flood control. As an on-stream reservoir, it fills in winter and spring and releases irrigation water and water for aquatic species from late spring to early fall.


100 There are three storage accounts on McKay Reservoir included in the model. Allocation to the 101 individual accounts occurs after system fill date and is proportional. Westland Irrigation District 102 (WID) has 32,054 acre-feet of storage in McKay. Stanfield Irrigation District (SID) has a storage 103 right in McKay but exchanges it for aquatic species purposes as part of the Umatilla River 104 exchange (Reclamation, 2014) in exchange for water from the Columbia River. This account, 105 now called the Fish account, has a storage capacity of 27,333 acre-feet. The National Marine 106 Fisheries Service (NMFS) started requiring a 10-cfs bypass flow into McKay Creek in 2004 as 107 part of a Biological Opinion (NMFS 2012). If 10 cfs of water is not available to release from 108 McKay via natural flow, water is released from the Fish account to make up the difference 109 between 10 cfs and the natural flow. Private storage for various private users along McKay 110 Creek and Umatilla River make up at total of 5,982 acre-feet of McKay Reservoir storage. 111 McKay Reservoir also has 165 acre-feet of residual storage that was not included in the model. 112 Error! Reference source not found. shows an illustration of McKay’s storage account 113 allocation and capacities. 114

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117 118 119

Figure 4: Illustration of McKay Reservoir storage allocation and capacities (not to scale).

The reservoirs are set up in RiverWare using Reservoir objects. The objects require information that defines the physical properties of the reservoirs including maximum volume, elevation-volume tables, elevation-maximum outflow tables, and elevation-area tables. The data to support these properties was supplied by Oregon Department of Water Resources (Giffin, 120 personal communication 2016). General features of the two reservoirs are shown in Table 1. 121

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123

Capacity 71,534 acre-feet

Flood Space 6,000 acre-feet

WID 32,054 acre-feet

SID/Fish 27,333 acre-feet

Private 5,982 acre-feet

Residual 165 acre-feet


124

125 Table 1: Maximum storage, maximum outlet capacity, and maximum spillway capacity of 126 simulated reservoirs.

127 The two reservoirs experience evaporation and seepage. Evaporation is calculated as the average 128 daily rate multiplied by the surface area of the reservoir at a given timestep. Seepage is estimated 129 using a volume-seepage curve developed from historical data for each reservoir. As the volume 130 of water in the reservoir increases, the seepage from the reservoir also increases.

131 3.2.3 Diversions

Reservoir Maximum Storage (acre-feet)

Maximum Outlet capacity (cfs)

Maximum Spillway capacity (cfs)

Cold Springs Reservoir 61,063 600 28,151

McKay Reservoir 82,359 1,200 27,000

132 133 134 135 136 137 138 139 140 141 142

Water is diverted from the Umatilla River primarily for agricultural uses, and to a lesser extent, municipal, and industrial uses. The water is transported to its areas of use via an extensive network of canals. For the purposes of this study, points of diversion (PODs) were aggregated into major canals and one POD in each reach for private diversions. Table 2Error! Reference source not found. lists the diversions and their respective reaches. Each diversion location can divert live flow, stored water, or both depending on the defined water rights; water rights are discussed in section 3.2.4. The diversions are simplified representations of the physical system and are not fully representative of the distribution system within a district. Canal and on-farm leakage within a district are not represented geographically in the model but are spatially aggregated and represented in the relative terms to other important features.


143 Table 2: Average annual diversion for each Water User in the model.

144 The model uses historical daily diversions as measured by Oregon Department of Water 145 Resources where data was available. When daily data was not available, daily patterns were 146 estimated from measured monthly diversions.

Model Water User Name Entity Reach Average Annual Historical1

Diversion (acre-feet) Private_McKay Private McKayCreek 457

Private_PdtoYoko Private BirchYoko 1,297

Furnish SID and Private YokoUmuo2 35,081

Feed HID YokoUmuo2 62,853

Private_YokoUmuo Private YokoUmuo 830

Westland WID and Private UmuoUmdo 69,127

Allen Allen UmuoUmdo 2,776

Dillon3 Dillon UmuoUmdo 1,989

Private_UmuoUmdo Private UmuoUmdo 175

WestExtension WEID UmdoUmao2 36,345

Maxwell HID UmdoUmao 10,089 (7,462 from ALine)4

Westland_Lower WID UmdoUmao 780

Private_UmdoUmao Private UmdoUmao 12,183

Private_UmaoColumbia Private UmaoColumbia 2,080

ALine HID Cold Springs Reservoir

43,278

147 148 149 150 151 152 153 154 155 156 157 158 159

1 The average annual historical diversion is the average diversion from 1994-2019 and include exchange water 2 Diversions that include exchanges 3 Dillion Canal usage ended in 2018, and the diversions served through the Westland Canal 4 In addition to diverting water from the Umatilla, the Maxwell Canal gets water from the outflow from the ALine canal. The amount in paranthesis is the average annual volume of water from the ALine canal, the remainder of the total is obtained from the Umatilla River. In the model, this is configured such that the Maxwell diversion requests the difference of the total and the ALine outflow.

3.2.4 Columbia River Exchanges

Water exchanges allow water to be left in the Umatilla River during critical periods for aquatic species and to date have been implemented in two phases. The Phase 1 exchange built the infrastructure to pump water from the Columbia River to exchange with WEID’s Umatilla River live water supply, which occurs in real-time during the irrigation season. The Phase 2 exchange built the infrastructure to pump water from the Columbia River to exchange with HID’s Umatilla River live water supply and both SID’s Umatilla River live water supply as well as their McKay Reservoir stored water. The HID exchange involves accumulating credits through leaving water in the Umatilla River from November 2 through May and using these credits to pump water from the Columbia River during the summer months. The SID exchange occurs in real-time during the irrigation season. All three exchanges are operated to maintain a minimum target flow in the Umatilla River (Table 3). Table 4 shows operational data for the different phases.


160

Phase Year Began Columbia River Pumping Rates (cfs)

Irrigation Districts Pumped Water Location

Phase I 1993 140 WEID WEID Main Canal

Phase II 2000 240 HID, SID Cold Springs Reservoir and SID’s Furnish Canal

161 Table 3: Umatilla River target flows at UMDO

162

163 Table 4: Operational Data for Phase I and II

Time Period October – November 15

Flows (cfs) 300

November 16 – June 30 250

July 1 – August 15 75

August 16 – September 30 250

164 In the RiverWare model, all three of the exchanges are modeled with similar rules, but different 165 parameters. The different parameters for the individual exchanges are in Table 5. The exchanges 166 167 168 169 170 171 172 173

174 175 176 177

Table 5: Exchange Rule parameters

Exchange Live Flow Hydromet Location

Canal Operational Effectiveness (cfs)

5-Day Average Buffer Flow (cfs)

Type of Exchange

HID UMUO 80 300 Credits accumulated

SID UMUO 20 100 Real time exchange

WEID UMTO 20 50 Real time exchange

occur when the live flow less the target river flows5 and the canal operational effectiveness6 do not meet the diversion request. In order to divert Umatilla River water to the canals, there must be enough live flow predicted in the Umatilla River for 5 consecutive days which is modeled using a 5-day average forecast. The average forecast includes a buffer flow that was selected for each canal to account for differences between human decision and a perfect forecast. If the canal does not divert due to insufficient flows in the Umatilla River, the total diversion is exchanged for pumping water from the Columbia River; otherwise, only the part of the diversion that cannot be met is exchanged.

Additionally, due to a low canal efficiency in HID’s Feed canal, exchange credits are accumulated based on a 20% loss. In real time, the Feed canal can lose upwards of 30% of the diverted water. The RiverWare model only allows for 20% loss of the diverted water, with the remaining lost water embedded in the gains and losses.

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5 Target river flows are found in Table 3 and vary monthly. 6 The canal operational effectiveness is the minimum flow a canal needs to divert.


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3.2.5 Water Rights

181 In order to ensure that water is distributed in the Lower Umatilla River Basin according to the 182 limitations imposed by water rights, the RiverWare models uses the water right accounting 183 function SolveWaterRights. This function distributes available live flow to accounts assigned to 184 Water Users within the model using their water right priority.

Three types of water accounts are defined in this model: live flow diversion, live flow storage, and stored water. The live flow diversion accounts are associated with Water User objects and 186 have a priority date and maximum flow diversion rate. The live flow storage rights are associated 187 with Reservoir objects and have a priority date and maximum storage volume. The stored water 188 rights are associated with the Water User objects and can request water stored in the reservoir 189 storage accounts. The individual water rights are listed in Appendix B.

Natural flow water rights data were supplied by OWRD (Hendricks, personal communication). 191 Storage water rights data were collected from Reclamation records. 192

3.2.6 Groundwater Response Functions 193

The model calculates return flows that result from canal seepage and on-farm infiltration. Figure194 5 illustrates the calculation that RiverWare used to determine the return flow to each river reach in the model. When a Water User object diverts water from the river, a portion of that water is 196 assumed to be consumptively used. The remaining fraction (i.e. the return flow fraction of the 197 diversion) of water returns to the river via overland flow or via the aquifer. This fraction was198 input to the model using the Periodic Fraction, p, slot on each Water User object. The periodic 199 fraction reflects estimates of canal seepage or on-farm infiltration. The return flows can return to different reaches of the river and the proportion in which they return to each reach was assigned 201 in the Return Flow Proportion table.202

Details about the interaction of surface water and groundwater came from modeling work that 203 was previously completed by Natural Resources Consulting Engineers (NRCE) for the Bureau of 204 Indian Affairs (BIA). Response functions were developed using variations on a time-dependent MODFLOW model of the Lower Umatilla River Basin (NRCE 2001) and the methods described 206 in Johnson and others (1998). The time lag function that determines when the water returns is 207 described by a response function, also developed using a MODFLOW model of the Lower 208 Umatilla River Basin and the methods described in Johnson and others (1998). The response209 functions were assigned to the Multi-Return Lag Coeffs table on each Water User object.

211 212 213 214

It is important to understand that the return fractions and response functions that were generated by the MODFLOW model only describe the fate of the water once it becomes return flow. It does not determine the amount of water that becomes return flow. If changes to the system occur that increases canal or on-farm efficiency, these changes are reflected in the Periodic Fraction, but the return fractions and response functions stay the same. The only time the return fractions


216 and response functions would change are when significant changes to the aquifer gradients 217 change that would impact where and when water would return to the river.

Diversion, D

Periodic Fraction, p

Returned Flow, R = D * p

Consumptive Use, C = D * (1-p)

GW Return to Reach 1, GWr1 = R *x1

SW Return to Reach 1, SWr1 = R *x2

GW Return to Reach 2, GWr2 = R *x3

SW Return to Reach 2, SWr2 = R *x4

t t tt

GW Return to Reach 1 at t, GWr1t = R *x1*RF1(t)

RF

1

RF

2

RF

3

RF

4

SW Return to Reach 1 at t, SWr1t = R *x2*RF2(t)

GW Return to Reach 2 at t, GWr2t = R *x3*RF3(t)

SW Return to Reach 2 at t, SWr2t = R *x4*RF4(t)

Return Flow to Reach 1 at t, RF1t = GWr1t+ SWr1t

Return Flow to Reach 2 at t, RF2t = GWr2t+ SWr2t

Return Flow Proportion, x

Return Flow

Multi Return Lag Coeffs, RF

218

219 Figure 5: Illustration describing the return flow calculation within RiverWare Water User objects.


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