Arkansas River Basin raw water storage requirements

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Table of

TABLE

OF

Table of

LIST OF

TABLES

Description _{Pane No.}

Table ES-1 Water System Planning Data ES-1

Table ES-2 Summary of Storage Requirements _ES-3

Table ES-3 Summary of Results of Fry-Ark System Simulation 1 _ES-4

Table 1.1 Storage Space Allocation 3

Table 2.1 Operating Principles for the Fry-Ark Project ₈

Table 4.1 Classification of Native Arkansas River Flow Data at Pueblo Dam 15

Table 4.2 Senior Priorities for Exchange in Pueblo Reservoir 18

Table 4.3 Divertable Native Flow Above Pueblo Reservoir 21

Table 4.4 Divertable Native Flow at Mt. Princeton 22

Table 4.5 Summary of ARKEX Output Used for MODSIM Runs 24

Table 4.6 Summation of Scenario #1A Exchange Potentials 25

Table 4.7 Summation of Scenario #1B Exchange Potentials ₂₆

Table 4.8 Summation of Scenario #2A & #3A Exchange Potentials • . • • • • • OOOOOOOOO • • . . 27

Table 4.9 Summation of Scenario #2B & #3B Exchange Potentials 28

Table 4.10 Summation of Scenario #2A & #3A _{Exchange Pot. w/Req. Streamflows 29}

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Table of

LIST

OF

FIGURES

32

37 44

Description _{Page No.}

Figure 1.1 Colorado Springs Water Supply System ₄

Figure 1.2 Network Schematic 6

Figure 4.1 City of Colorado Springs' Stipulated Exchanges ₁₉

Figure 6.1 Scenario #1 Schematic 40

Figure 6.2 Pueblo contents for run #1A 41

Figure 6.3 Pueblo contents for run #1B ₄₂

Figure 6.4 Scenario #2 Network Schematic 47

Figure 6.5 Elephant Rock Contents for Run #2A 48

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Table of

Executive Summary

ARKANSAS

RIVER BASIN

RAW

WATER

STORAGE

REQUIREMENTS

EXECUTIVE

SUMMARY

Objective ,

The objective of this project was to examine the City of Colorado Springs' (City) raw water storage

requirements, availability, and opportunities in the year 2042. The storage requirements were based on the

projected need for a new raw water delivery system capable of conveying an additional 30,000 acre-feet to the City. After the City's storage requirements were calculated, an analysis of the Fryingpan-Arkansas

(Fry-Ark) system was completed to determine if the future storage required by the City is available in

existing Ark reservoirs. The analysis of the Ark system included both current and projected

Fry-Ark operations and allocations, and was conducted so that any utilization of Fry-Ark storage space would

not interfere with transmountain Project yields or operations.

City of

Colorado Springs'

Storage Requirements

Demands

Water demand and reusable return flows were key variables in this analysis and are summarized in Table' ES-1. Colorado Springs Utilities Water Resources Department calculated the monthly demand for

additional first-use water, reusable wastewater return flows to Fountain Creek at the outfall of the Las Vegas Wastewater Treatment Plant, and reusable return flows at the confluence of Fountain Creek and

the Arkansas River. Demands and return flows were determined for years 1993, 2012 and 2042. The City's

1993 data was derived from actual consumption figures for calendar year 1993. At the projected 2012

demand, the City's existing raw water delivery systems will be very near design capacity. The projected

demands in 2042 are for the City's current 50-year planning horizon. Based on current predictions, the City

will require 30,000 acre-feet of additional delivery capacity to meet the 2042 demands.

Table ES-I Water System Planning Data Year Population Demand (at) Water Supplies

, Exchangeable Water Avail. at the Ark. River (at) Native (at) ' Transmtn. Imports (at) Exchanged Waters (at) 1993 309,000 73,737 17,227 53,662 2,848 19,057 2012 458,000 107,000 26,000 65,500 15,500 36,943 2042 ' 610,000136,800 26,000 65,500 45,300 55,799 .

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Executive Summary

Delivery Alternatives.

To determine the City's raw water storage requirements in the Upper Arkansas River Basin, three different development alternatives were evaluated. The first alternative uses existing space in Pueblo Reservoir to store exchange water before it is pumped to the City. Water would be conveyed in a proposed pipeline which would roughly parallel the existing Fountain Valley Authority pipeline. The second alternative stores water in the proposed Elephant Rock Reservoir north of Buena Vista, Colorado, before it is pumped to the City. This alternative conveys water in a proposed pipeline which would closely parallel the existing Homestake pipeline. The third alternative is similar to the second, except that exchanged water would be pumped directly from the Arkansas River without the benefit of on-stream storage. A key factor for each of the alternatives is the use of the City's Arkansas River Exchange Decree to move reusable water from the confluence of Fountain Creek and the Arkansas River, upstream on the Arkansas, to the proposed point of diversion.

Methodology

The storage requirements were determined using MODSIM, a river basin network flow model. The model was configured to include the river systems, reservoirs and pipelines involved in each alternative. The exchange potential on the Arkansas River was calculated on a daily basis for water years 1966 through 1990, and then summed to monthly totals. This monthly total along with the monthly demands and monthly return flows were then used as input data to the MODSIM model.

Key factors in the analysis of the Arkansas River data for the purposes of determining the exchange potential are senior exchanges and water rights in the Arkansas River. Eight different exchanges were identified which affect the City's present and future exchange operations on the river. Decrees and stipulations were analyzed to establish flow and quantity limits, the impacted reach of the river, and the priority and operation of such exchange rights. All exchanges are operated so that no injury occurs to senior water rights. The study also complies with decree and stipulation requirements, such as the exchange restrictions during the winter water period.

The MODSIM model was then run in successive trials, whereby the reservoir storage volumes were systematically reduced from the site capacity downward, until the City's projected demand could no longer be met. The _{smallest reservoir size which enabled the City's demands to be met is the minimum size that} should be considered for that alternative. Each of the three alternatives was modeled both with and without Williams Creek Reservoir, which was used to store and release exchangeable water, thus helping to take advantage of periods of high exchange potential on the Arkansas River. In order to determine the effects of the USBR _{streamflow augmentation program on reservoir sizing, the Elephant Rock Reservoir and Mt.} Princeton Diversion alternatives were modeled with and .without the USBR streamflow augmentation at the Wellsville gage.

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Executive Summary

1

Results

Ten combinations of _{storage and required streamflow for the three alternatives were modeled. Of}_these

ten, five were able to deliver the City's projected year 2042 _{demand without additional storage in the upper}

basin to augment streamflows at the point of diversion. The requirements for storage for the scenarios which could deliver the City's projected demands are summarized in Table ES-2.

Table ES-2 Summary of Storage Requirements'

Scenario Number and Description

Meets City Demand? _

' Active Size in Acre-Feet Pueblo Reservoir Elephant Rk I Mt. Princeton Williams Creek Res. , 1A - Fountain Creek to Pueblo Reservoir

Without Williams Creek Reservoir

Yes 5,000 ._., ...,

1B - Fountain Creek to Pueblo Reservoir With Williams Creek Reservoir

Yes 5,000 — ...

2A - Fountain Creek to Elephant Rock Reservoir Without Williams Creek Reservoir

Yes ... 18,000 ...

28 - Fountain Creek to Elephant Rock Reservoir With Williams Creek Reservoir

-Yes ...HO

11,000 6,000

2B - Fountain Creek to Elephant Rock Reservoir With Williams Creek Reservoir

With 250/750 cfs streamflow augmentation _, Yes A _..., 15,000 , 4,000 ,. , 'From Table 6.3

Fry-Ark Project Storage Space Availability

The Southeastern Water Conservancy District controls a total of 305,401 acre-feet of active conservation

storage in Pueblo, Twin Lakes and Turquoise reservoirs. To determine the amount of conservation storage,

if any, that is beyond the amount required to manage the Fry-Ark Project, a MODSIM model was

configured to simulate Project operations. The Fry-Ark system was then modeled using both historical and

projected future demands for Project water.

Institutional Parameters

A total of 349,940 acre-feet of storage space is available in Pueblo Reservoir of which 26,991 acre-feet is

required year-round for flood control storage. An additional 65,954 acre-feet joint-use pool is used for flood control storage from March 16th through November 14th, and for conservation storage from November 15th through March 15th. Hence, the space in Pueblo Reservoir available for conservation storage fluctuates between 228,874 and 294,828 acre-feet.

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Executive Summary

1

Current allocation principles allow municipal entities to use their storage space to carry water over from year to year, while agricultural entities may not carry water over. Municipal allocations may use up to 51

percent of the water diverted in the current year, and agricultural allocations may use up to 49 percent of

the water delivered in current year. While unallocated water can go to either municipal or agricultural users, only agricultural users have requested and taken delivery of unallocated water between 1986 and 1991.

Methodology

The estimation of the space required by the Project was completed in two steps. First, historical yields and

allocation percentages were input to the model, and the model calibrated until the output balanced with

the historical allocations. Second, the Model was run with the parameters derived in the calibration phase,

estimated Project yields, and estimated agricultural and municipal allocations. Project yields were estimated

by the U.S. Bureau of Reclamation for their Fryingpan-Arkansas Operations model, and included the water

years from 1966 through 1990. Current allocation percentages and rules were used in the 25 years modeled, including the presumption that agricultural interests would take 49 percent of annual yield, and that they would not be able to store water from year to year. Municipal entities were allocated 51 percent of the annual yield, but took varying percentages of their water, depending on the year's classification as wet, average, or dry.

Results

Table ES-3 shows that when the projected agricultural and municipal demands were modeled using the Bureau's estimated Project yields, there was space allocated to Project storage which was not required for

Project management, and which could have been used by other entities.

Table ES-3 Summary of Results of Fry-Ark System Simulation

Reservoir ' Maximum Storage Required (Acre-Feet) Allocated Project Storage (Acre-Feet) . Minimum Available Conservation Storage . (Acre-Feet) Total Storage

in Turquoise, Twin Lakes and Pueblo reservoirs

212,8732 , _ 305,401" (during summer) 92,528 Pueblo Reservoir 170,996 1 228,874 1.2 (during summer) , 57,878

1 Active Storage only. •

2 Allocation during the summer months, when the joint-use pool is not available for conservation storage.

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Chapter 1 Introduction

1 CHAPTER

1:

INTRODUCTION

Project Background and Scope

Colorado Springs Utilities (City) performed extensive studies of raw water delivery alternatives in the

Upper Basin of the Arkansas River in 1989. The City's storage contracts in the upper basin are coordinated

with the Fryingpan-Arkansas Project, which is operated by the U. S. Bureau of Reclamation (USBR) and

managed by the Southeastern Colorado Water Conservancy District (SECWCD) in Pueblo. The City

requested Gronning Engineering Company (GEC) to investigate the possibility of using a USBR computer

model known as the Fryingpan-Arkansas Operations Model (FAOP) to simulate operations of the Fry-Ark

Project. This investigation indicated that the FAOP model could simulate the Project operations under a

limited set of operating rules but was not satisfactory for the purposes of accommodating exchanges or simulating scenarios currently in operation by the Colorado Springs Utilities and other water users in the

Arkansas River Basin (GEC, 1992).

In September 1992, the City entered into this most current phase of its raw water supply planning effort. The objective of this project is to analyze alternatives available to the City for raw water storage using existing facilities in the Fry-Ark System. This is accomplished using computer models to simulate the behavior of these facilities over an extended historical period. This report documents the results of the water storage analysis.

To frame the results of the investigations, three time horizons have been selected. The first, year 1993, is

the current time period. The second, year 2012, is the 20-year planning horizon and when the City's existing

raw water delivery systems are projected to reach capacity. The third, year 2042, is the current 50-year planning horizon. While this report, considers possible facilities to meet demands during the 50-year

planning horizon, the City intends to continue development of its exchange programs, reuse programs and

necessary facilities in order to meet demands anticipated beyond the planning horizon. No intent to abandon any water rights or facilities is implied in this report due to the selection of the 50-year planning horizon for purposes of this report. Also, while this study calculated the storage required to meet the

projected 2042 demands, actual reservoir sizes may _{be larger due to water rights issues, yield safety factors,}

the economies of scale, recreation, or other uses.

This report is divided into three main parts. Chapters 2 and 3 detail the approach that was utilized to

model the Arkansas Basin and how computer models were applied in this study. Chapters 4 and 5 focus

on the data that was required for the computer models to generate the results of this investigation. Finally,

Chapters 6 and 7 detail specific facets of the modeling process and the results of the investigation.

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Chapter 1 _Introduction

Project Objectives

The following are objectives of the investigation:

1. Using the historical records and data, determine storage requirements in the Upper Basin Reservoirs for the year 2042 under several development scenarios.

2. Using storage requirements generated in Objective 1, determine the amount of storage space available in existing Fry-Ark Reservoirs, or required by a new reservoir in the Upper Basin.

Basis of

Raw Water Delivery Alternatives

The City completed the Raw Water Supply Evaluation by Black & Veatch Consultants (B&V) and GEC in 1989. That study presented four basic Alternatives to expand the City's raw water storage and delivery system into the future:

A. Main stem storage on the upper Arkansas River — Elephant Rock Reservoir (proposed), located in the vicinity of Elephant Rock, north of Buena Vista (see Figure 1.1), would divert and store flows for delivery to the City.

B. Pueblo Reservoir — Raw water supplies would be developed from the Arkansas River with regulation storage or diversion on the Lower Arkansas River by raising the dam at Pueblo Reservoir to create additional storage space for the City.

C. Lake Meredith System — Expand the storage in the Colorado Canal system's Lake Henry and Lake Meredith. Convey the stored water to the City through a new pipeline/pump station system.

D. _{Storage Contract Alternatives — Contractual alternatives consist of procurement of additional storage} space in existing reservoirs through contract with other entities, or negotiation of exchange agreements with other entities.

In 1994 Black & _{Veatch completed an update to the raw water delivery report. In the revision, seven of} the alternatives were eliminated from further consideration at this time (B&V, 1994), and the four were updated. _{The alternatives eliminated included the alternatives for raising Pueblo Dam and for expanding} storage in the Colorado Canal System. Consequently, this report dealt with the updated Elephant Rock • Reservoir, Mt. _{Princeton Diversion, and the possibility of Fry-Ark Project storage available.}

The City filed on the Elephant Rock Reservoir site in 1990 in Case No. 90-CW-56. Existing storage was considered in the three east slope reservoirs of the Fry-Ark Project: Pueblo Reservoir, Twin Lakes Reservoir and Turquoise (Sugarloaf) Reservoir. Data on these reservoirs is presented in Table 1.1.

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MIN I= 111111 NMI 1E11 IIIIII NMI 11111 NIB 011111 11111 IIIIII 11111 11111 111111 MI MO Table 1.1 Upper Arkansas River Basin Storage Space Allocation (*) Values in Acre -Feet Reservoir Colorado Springs Other FVA Pueblo Aurora Municipal E of Pblo Municipal _W. of Pblo Other Twin L Co. Ag Interests

Total Conservation Storage

Turquoise contract 32,416 (1) 5,000 (2) 20.000 (3) SECWCD 12,216 (8) 30,900 100,532 Twin Lakes contract 29,757 (4) 12,602 (4) 2.673 (4) 9,420 (4) SECWCD 6,598 61,050 Pueblo contract 54,520 (5) 21,830 (5) 30,540 (6) 36,648 (7) SECWCD 112.148 255.687 (9) Sub Total 116,693 21,830 48,142 22,673 36,648 12,216 9,420 149,646 (10) 417,269 (11: Clear Creek 11.440 11,440 Total 116,693 21,830 59,582 22,673 36,648 12,216 9.420 149,646 428,709 (*) Refer also to Table 2.1 for allocation of Fry -Ark storage space. (1) 15.000 AF Homestake + 17.416 AF CF&I (2) 5,000 AF CF&I (3) 15,000 AF Homestake + 5.000 AF CF&I (4) Twin Lakes Canal and Reservoir Co. (5) 76.350 AF (54,520 + 21,830) of FVA space (25% of total FVA conservaion space) assumed to be in Pueblo for convenience. (6) 30,540 AF of Pueblo's space (10% of total) assumed to be in Pueblo for convenience. (7) 36,648 AF of municipal space (12% of total) assumed to be in Pueblo for convenience. (8) 12,216 AF of municipal space (4% of total) assumed to be in Turquoise for convenience. (9) Pueblo Reservoir 1993 Sedimentation Survey (10) 149.646 is approximately 49% of 305.400, apportioned between reservoirs. See Table 7.1. (11) 417,269 AF (conservation) + 69.024 (dead) + 44.780(inactive) + 26,991 (flood) + 65.954 (joint) = 624,018 AF (Total Project storage). PAPROJECINGEC\323\REPOM\STOR_TBLWOl

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• t o 4/ • GL E FRYINGR4 EAGLE CROSS CR. E.CROSS CR. W. CROSS CR. RUEDI RES. 0 0 N). ASPS 0 _HUCR DILLON RES FALL CR HOMESTAK 0 ME HEDGE PPEff 51 I y H NEST ftES. MONTGOMERY \ t•L RES. — — NJ" fx • LEADVILLE MY ELBERT I I IT (useR) _FAIRPLAY

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• GROUND WATER SUPPLY ( WELLS )

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HOMESTAKE COLLECTION SYSTEM —PHASE

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HOMESTAKE COLLECTION SYSTEM —PHASE TE*

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HOMESTAKE COLLECTION SYSTEM—EAGLE/ARKANSAS DIVISION*

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FRYINGPAN—ARKANSAS COLLECTION SYSTEM

0

TWIN LAKES COLLECTION SYSTEM

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BLUE RIVER COLLECTION SYSTEM

0

PIKES PEAK COLLECTION SYSTEM —NORTH SLOPE

0

PIKES PEAK COLLECTION SYSTEM —SOUTH SLOPE

• NORTHFIELD COLLECTION SYSTEM

• ROSEMONT COLLECTION SYSTEM

• COLORADO CANAL •.=,;',3 c 0 T TO Alt+ 0 c:, CSO t.V.,..11 SHAVA NO 'PEAK SALIDA DENVER c, AURORA 42-IJ • LIMETON 0 C. RAMPART/ RES WOODLAND PARK = • PIKES CRIPPLE CREEK 0 MID BEAVER CR. W. BEAVER CR. CANON CIT ® CASTLE ROCK 4 , PALMER LAKE 1. -A

COLORADO

SPRINGS

WATER

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Figure 1.1 Raw Water Supply System

LA JUNTA

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Chapter 1 Introduction

Raw Water Delivery Systems

For the purpose of _{identifying storage opportunities, this study focused on existing and proposed pipelines} to be used by the City to convey raw water from the source of supply to terminal storage and treatment near the City. The City now has three pipelines for its upper Arkansas River Basin and transmountain sources as shown _{in Figure 1.1. Since the Blue River conveys water from the Colorado River and the Platte} River basins, it was not included in this study. The existing pipelines of importance to the analysis are the Homestake pipeline and the Fountain Valley Authority (FVA) pipeline. Data on the City's raw water system are contained in the Appendix. .

Once capacities in the existing delivery system have been reached, new elements in the delivery system must be ready to come on-line, or other steps must be taken to balance deliveries and demands in the City's system. The new elements, i.e., intakes, pumping stations and pipeline, shown in Figure 1.2, are addressed in above-mentioned alternative schemes. For the purposes of this investigation, two new pipeline alternatives are being considered. They are formulated around the proposed delivery systems:

Scenario 1: _{parallel the Fountain Valley Authority pipeline from Pueblo Reservoir to terminal storage near} the City, as shown in Figure 1.2. This system is called the "Front Range pipeline system".1

Scenarios 2 _{and 3: the Elephant Rock / Mount Princeton system, from a new diversion point on the} Arkansas River above Buena Vista, over the Mosquito Range to terminal storage near the City. This pipeline is shown in Figure 1.22 as the "Mosquito Range pipeline".Scenario 2 includes the construction of Elephant Rock Reservoir. Scenario 3 includes the construction of Mr. Princeton Diversion. Detailed definition of the scenarios and analysis is presented in Chapter 6.

City of

Colorado Springs' Current Project Storage

The City currently has contracted space in Fry-Ark Project Reservoirs. Table 1.1 shows the amount of space the City and other municipalities have contracted in Project Reservoirs. The storage space numbers were obtained from the U.S. Bureau of Reclamation and the Cities of Colorado Springs, Aurora and Pueblo. The Fry-Ark Project is described in more detail in Chapter 2 and more discussion regarding storage space in Project reservoirs appears in Chapter 7.

1

Relates to B&V alternative B4 and D3. _{Alternatives shown in Figure 20 of B&V}report.

2Relates to B&V alternative D1 and shown in Figure 28 of the B&V report.

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EMI IIIIII 11111 111111 Mill 111111 INN 1111111 IIIIII MN 1110 11111111 IIIIII 11111 MI 11111 =I

61'

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HOLs ESTAx PROJECT 1.1014100 LIE RY RESERVOIR L % SC '. .14NEY IJOUNTAN R (SERVO • .. , , i SOU= MATTI ILTV1CR BASIN DEM ON 1 r....i...—...:-lr.. iv —...---..--.i r .--...--...--...—...—.1.IMIIIMMMII..II.M.MIM...OMMIMDOIIIMIIIIIMIMIMNIIaIIIIP././/MN.•I.Miaii...e ftimorr''' S % 1 \,L,%,%, LMAR.CRUX rACILI T1 ES DEVIM14 1 FO i ‘s A s . t Ns $ KAI PING PLANT (Si SLOP I MING PAN -ARKANSAS I I 1 KNICSTAX Twin. PROJECT I I I , UT EL BERT t EOREDAY i i 4, 0 1 ' (44 I ' • I .Z' , I t I i 4i 1/

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LAS ANIMAS CACC FIGURE 1.2 COLORADO SPRING'S RAW WATER SYSTEM ABOVE THE LAS ANIMAS GAGE ttat 11011911p0.11UI

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Chapter 2 _{Approach to Arkansas Basin Modeling}

CHAPTER

2:

APPROACH

TO

ARKANSAS

BASIN

MODELING

Introduction

The approach used to simulate the Arkansas River Basin above Pueblo Reservoir, hereafter called the "upper basin", consisted of modeling only system components that could impact the results. As mentioned in Chapter 1, several entities utilize storage space and other system components such as conduits in the upper basin. For the purposes of this investigation, all system components in the upper .basin were originally considered. After careful examination, system components whose impacts were judged to be independent of the final results were eliminated from the modeling process. For example, the City of

Aurora owns water that is stored in upper basin reservoirs. However, since the amount of stored water

owned by Aurora has no effect on the amount of storage required by the City of Colorado Springs, water owned by Aurora was eliminated from the modeling process. Other features not incorporated in the modeling include Clear Creek Reservoir, the Busk-Ivanhoe system, or any west slope facilities. System components such as raw water delivery pipelines, Arkansas River flows, and reservoirs in which the City can store water were selected for the modeling process, and are described later in this chapter. .

Fryingpan-Arkansas Project

The Fry-Ark Project, authorized under Public Law 87-590 on August 16,1962, is a transmountain diversion

project which imports water from the western slope of the continental divide to the eastern slope (USBR, 1988). Planning studies conducted during the 1940's and 1950's indicated that the Fry-Ark Project was

beneficial because a shortage of _{irrigation water existed virtually every year in the Arkansas Valley}_(USBR,

1990). The primary purpose of the Fry-Ark _{Project is to provide supplemental water to both municipal and}

agricultural users. The primary storage components of the Fry-Ark Project are Turquoise Reservoir, Twin Lakes Reservoir and Pueblo Reservoir, shown in Figures 1.1 and 1.2.

•The Operating Principles for the Fry-Ark Project, as amended December 9, 1960, were adopted by the State of Colorado, Colorado Water Conservation Board, Southeastern Colorado Water Conservancy District, Colorado River Water Conservation District and the Southwestern Water Conservation District

(USBR, 1990). The Operating Principles, in essence, set limitations on diversions of west-slope water into

the transmountain tunnels. In 1979, the SECWCD approved the "Allocation Principles, Findings, Determinations, and Resolutions" which document the principles for the allocation of Project water to

municipal and agricultural water users and the use of Project storage by municipalities (USBR, 1990).

Table 2.1 details important facets of _{the Operating Principles, Allocation Principles and the spill priorities}

for water stored in Project reservoirs.

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1

Chapter 2 Approach to Arkansas Basin Modeling

Table 2.1 Operating Principles, Allocation Principles and Order of Spills for the Fryingpan-Arkansas Project (USBR 1990) Operating Principles:

,

(April 30, 1959) 1. West slope diversion may not exceed 120,000 2. Diversions in any 34 consecutive year 3. The Project will be operated so that domestic

for any other purpose.

c

-acre-feet in one year.

period may not exceed 2,352,800 acre-feet.

Z ' •"' i water users have preference over those using water the greatest benefit from the use and reuse of imported

in Colorado. , _—

4. The Project will be operated to achieve Project waters within the Project boundaries Allocation Principles:

1. A minimum of 51 percent space in Project reservoirs divided as follows (the annual acre-feet):

(Southeastern Colorado Water Conservancy District, Pueblo 1979)

of the annual Project water supply and 159,000 acre-feet of carryover storage is allocated to municipal and domestic use. The water and storage allocation is water allocation is based on an estimated total annual project yield of 80,400 Fountain Valley

Pipeline ,

Cities and Towns East of Pueblo

City of Pueblo (Pueblo Board of

Water Works)

Cities and Towns West of Pueblo Annual Water Allocation (%) ' 25% 12% ' 10% 4% Annual Water Allocation (acre-feet) 20,100 9,648 8,040 3,216

.._

Storage Space (acre-feet) 77,940 37,410

_ 31,180 12,470 2. The

served. 2006.

water allocated to the Fountain Valley Authority (FVA) can be broken down further into the entities The amount allocated to each group is based on an annual allocation of 20,100 acre-feet in the year (Values below in acre-feet)

Colorado Springs _

Security Fountain Stratmoor Hills Widefield Water Allocation 14,353 1,646 2,000 601 1,500

3. The SECWCD Board acknowledges that the demands for the water allocated to municipal and domestic use quantified above will not be reached until some time in the future. If the water users above opt not to take their full allocation for many years, their allocation percentage will not be reduced or abandoned. 4. _{Irrigation water is allocated on an annual basis of need. Agricultural water users are not granted} carryover storage sp • e Allocation Principles or water allocated to them.

Project Reservoir Spill Order:

Water evacuated from Project purposes, storage of transmountain in the following order (from

1. If-and-when available 2. If-and-when available 3. Winter water in excess 4. Non-project water

boundaries of the 5. Winter water not 6. Project water accumulated

(1986)

Reservoirs to meet the necessities of or native Project water and Project the first to spill to the last to spill):

storage contracts for use outside the SECWCD

...-..---7

storage contracts for use within the SECWCD of 70,000 acre-feet.

flood control, power generation operational requirements is charged

boundaries. boundaries. within the tributaries. stored under contracts

District.

with municipal entities in excess of 70,000 acre-feet.

.___...---.

from the Arkansas River and its

PAPROJECINGEC13731REPOR1U'REIC1PLTBL

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1

Chapter 2 _{Approach to Arkansas Basin Modeling}

The SECWCD also manages a program known as the Winter Water Storage Program. The Winter Storage case was filed in District Court, Water Division 2 on December 26, 1984, and assigned Case No. 84-CW-179. The purpose of the Winter Water Storage Program is to store decreed water during the non-growing months of _{the winter in Pueblo Reservoir and other reservoirs in the Arkansas Basin. Winter Water can} be stored from November 15th through March 15th. The primary participants in the Winter Water Storage Program are major ditches and reservoirs with water rights senior to March 1, 1910.

Fryingpan-Arkansas Operation Model

The Fryingpan-Arkansas Operation Model (FAOP) was created by the USBR to help estimate the amount of _{west-slope water that could be delivered to the Arkansas Valley if the Fry-Ark Project were constructed.} FAOP is a demand driven, site specific model _{that predicts flows and reservoir contents on a monthly basis} for the Arkansas River to Pueblo Reservoir. The Operating and Allocation Principles are imbedded in the program code and control flows and storage capacities.

In 1990, the USBR restructured the original FAOP model. The model was modified primarily because the demands for Project water were well below the estimates from the original FAOP model. The results of the updated modeling process are contained in Review of Operations, Fryingpan-Arkansas Project, Colorado completed by the USBR in 1990.

The City obtained access to the FAOP model in 1992 and requested GEC to perform an assessment of the model for use in studying the City's raw water system. The City hoped to use FAOP to estimate storage requirements and storage availability in the upper basin. As previously discussed, FAOP was determined to be unsatisfactory for the City's intended use in 1992.

System Components

The modeling effort for this investigation focused on the components of the system that are controlled by Colorado Springs Utilities and reservoirs in which the City stores water. The following summarizes the major system components used in the model configuration. The storage and delivery components are shown in Figure 1.2.

supplies _{Historical raw water records were obtained from the USGS and the USBR.} Potential Fry-Ark Project yields were obtained from the USBR, data set of FAOP. Projected reusable return 'flows were determined by the City.

storage Required storage amounts _{for operations were calculated for Twin Lakes Reservoir,} Pueblo Reservoir, and Williams Creek Reservoir (proposed).

(20)

Chapter 2 _{Approach to Arkansas Basin Modeling}

delivery — _{Transmission of raw water from the Arkansas River to the City is via existing and} proposed pipelines.

demands — _{Demand for a new raw water delivery system were projected by the City for years} 1993, 2012, and 2042 (data developed in Chapter 5).

Arkansas River

System _{Historical daily records of 91 nodes on or near the Arkansas River System,} combined in the exchange model, ARICEX.

Model Selection

Since it was concluded that FAOP _{was unsatisfactory for the purposes of this investigation, other models} were considered. The MODSIM simulation and optimization model developed at Colorado State University is a modified version of a network model called SIMYLD II developed by the Texas Water Development Board in 1972. MODSIM has been applied to water resource analysis problems in Fort Collins, the Williams Fork of the Colorado River, City of Greeley, and the Colorado-Big Thompson Project. The attributes of MODSIM are that:

1. MODSIM _{can accommodate exchanges of water by accounting for flows in selected locations.} 2. _{MODSIM allows for the selection of operating priorities and reservoir target storage.}

3. MODSIM _{accepts data sets which are specialized for the objectives of this study.}

The project team at GEC has prior experience with MODSIM applications. Furthermore, model improvements and application consultation was available through Dr. John Labadie of Colorado State University. Dr. _{Labadie has extensive exp.erience with the MODSIM model and has access to the source} code and documentation. For the reasons outlined above, MODSIM was selected as the analysis tool to estimate storage requirements and opportunities in the Arkansas River Basin.

Exchange Operations

The supply/delivery scenarios for this Project depend on the ability to estimate the exchange potential on the Arkansas River. Because MODSIM _{has no standard routines to calculate exchange potential, GEC's} Arkansas River Exchange Model (ARICEX) _{was used in a two step process. First, ARICEX was used to} calculate the potential to exchange water upstream in the Arkansas River. The results from ARKEX were then added to the data set used by MODSIM. _{MODSIM was used to simulate interactions of storage,} water supply and demand. ARICEX is discussed further in Chapter 4.

(21)

Chapter 2 _{Approach to Arkansas Basin Modeling}

Important Modeling Considerations

There are several tenets in modeling that were maintained:

1. Mass balance was maintained at all points in the model. That is, at any point inflows minus outflows minus losses equals changes in storage.

2. Losses due to transit and evaporation were estimated using available data or operating experience. 3. Known upper and lower limits on capacities of all conduits and storage facilities were obtained

from existing records.

Scenario Variations

For each of Scenarios, 1, 2 and 3 (described in Chapter 1), two MODSIM model configurations were

constructed. A nomenclature of "A" and "B" was selected to distinguish the two variations of each Scenario. The following describes the variations:

"A": The model was constructed without Williams Creek Reservoir. Williams Creek Reservoir is a proposed reservoir that would be located near the City of Colorado Springs as shown in Figure 1.2. "B": The model was constructed with Williams Creek Reservoir. For the purposes of this investigation, Williams Creek Reservoir was utilized to store water discharged from the City's wastewater treatment plant to facilitate exchanges.

•

Fry-Ark System Simulation

A separate MODSIM model _{configuration and associated data sets were developed to estimate the amount}

of storage space available in Fry-Ark Reservoirs. Chapter 7 details the model configuration and results of

the simulation. Consistent with the second objective on page 2, an assessment must be made of the historical operation of the Fry-Ark Project and allocation of Project water. To accomplish this probable municipal and agricultural demands for supplemental water supply must be estimated, allowing for

allocation of _{water under current principles. Once these considerations are accounted for, a simulation can}

be conducted for behavior of the Fry-Ark System under historical conditions.

(22)

I

1 I

I

1 1•

I

1

Chapter 3 MODSIM

Model

Development

CHAPTER

3:

MODSIM

MODEL

DEVELOPMENT

MODSIM:

Definitions and Characteristics

MODSIM is a non-site specific model for which the user creates one file of system features and priorities,

and a second file containing flow data. MODSIM then uses these two files to optimize the usage of the available water — through routing and storage — to meet the demands following user specified priorities.

MODSIM _{can operate in one of three time steps: days summarized into weeks, weeks summarized into}

quarters, and months summarized into years. For this investigation, the monthly time step was selected.

The MODSIM model represents water systems as a flow network where each component can be assigned

minimum and maximum capacities. Therefore, all nodes and links must be limited by operating capacities

and parameters. The components of the system are represented in the network as nodes, both storage (i.e.

reservoirs) and non-storage (points of inflow and demand), and links (natural river reaches, canals and pipelines). Links allow the movement of water in only one direction. Losses due to evaporation and

seepage are calculated iteratively in each time step. All inflows, demands, seepage losses and return flows

must accumulate at nodes.

MODSIM

Data Files

The network organizational file (ORG file) contains descriptive data about the number and type of periods

being modeled, the number of nodes and links, the names, sizes and area-capacity curves of the system

reservoirs, system demands, link connections and capacities. The network data file (ADATA file) contains

the flow, evaporation and demand data that varies with each step for the historical period 1966 through 1990.

Three types of monthly flow data were input in the ADATA file: historical gage record, projected potential

hydrologic yield, and exchange potential data. The historical gage and potential system yield are monthly

values provided by the USBR, while the exchange potential was calculated as a daily value and summarized

in a monthly total by ARICEX.

Evaporation data for each reservoir was obtained from the USBR. These were corrected by regional

National Oceanic and Atmospheric Administration (NOAA) pan coefficients before being used in

MODSIM.

(23)

Chapter 3 MODSIM

Model

Development

Model

Documentation

Documentation detailing the modeling process and model configurations is found in a separate document entitled Arkansas Basin Raw Water Storage Requirements — MODSIM Documentation. The documentation includes a copy of the MODSIM model manual developed by Dr. John Labadie of Colorado State University. The manual _{describes the basic operations of}MODSIM, the coding of files and provides definitions necessary to execute

moDsrm.

_{Also included are coding forms developed by GEC} that were used to simplify the data entry process.

Model Verification

The MODSIM _{networks consider both exchange and Project water. By using gage record for the exchange} potential and requiring the model to maintain all historical deliveries, no other water users in the basin are injured. The model verification process included a• mass balance analysis of all river flows and diversions. To _{verify the network connections to the nodes (reservoirs and confluences), both input and} output data are compared to the network diagram by inspection.

Model Calibration

Historical data from the Fry-Ark Project was used to calibrate the model to estimate storage availability. The purpose of the calibration procedure was to conform the fixed operating variables, primarily losses from the system, to approach the real-world behavior of the verified system under study. Simulating evaporation rates and transit losses was the major focus of the calibration procedure.

Applications of

MODSIM

Separate model configurations were required for each of _{three Scenarios to estimate storage requirements.}

The

moDsrm

_{output are tabular data showing the reservoir contents throughout the study period. By}

analyzing the maximum and minimum reservoir contents and fluctuations in storage with the aid of spreadsheet software, quantitative results for the investigation were generated.

(24)

Chapter 4 _{Historical Flows and Exchanges}

CHAPTER

4:

HISTORICAL

FLOWS

AND

EXCHANGES

Historical Flows

Quantifying native flows, i.e. hydrology of the east slope watershed, is required for this study because several legal and administrative aspects of water management are tied to native water rights. Gage records of only native flow in the Arkansas River after 1928 are not available because transmountain diversions into the Arkansas River Basin delivered additional water to the river (USBR, 1969). For purposes of determining the amount of native flow in the Arkansas River, calculations which account for transmountain diversions in the total flow must be performed. The USBR calculated the yearly native flow in the Arkansas River at Pueblo Dam for purposes of their FAOP model study. The calculated yearly native flows for 1966 through 1990 at Pueblo Dam _{appear in Table 4.1 (monthly values in Table A.9). The annual yield} mean over the study period is calculated to be 528,576 acre-feet (at).

Wet

-Average-Dry

Year Classification

For the purposes of water management decision-making, it is helpful to characterize the hydrologic behavior of the watershed in terms of relative yield of _{water on an annual basis. The annual yield for each} of the years 1966 through 1990 were classified by GEC as either a wet, dry or average year based on the following procedure. All flows were ranked from smallest to largest with n = 1 being the smallest yearly flow.

For every year:

_P

_{= 11}

N

+1

where: n = rank position

N = number of years of data

P = _{the estimate of the probability that flow with rank n will not be exceeded.} Every year was then classified using the following equations:

Average

(A)

:

0.3

5_

P

_. 0.7

Wet( W)

:

P>

0.7 Dry

(D

)

:

P<

0.3

Table 4.1 shows the yearly flows and classifications. The wet-dry-average classification is utilized in Chapter 7 to make initial estimates of water demands and requirements for carry-over storage allocations.

(25)

Chapter 4 Historical Flows and Exchanges

Table 4.1 Classification of Native Arkansas River Flow Data at Pueblo Dam

(Listed in order of increasing annual flows, 1966-1990)

Year Calculated Flow (at) P Classification

1977 j -75c76 0 202,100 0.038 D 1981 (7) 6,7,4_00 290,500 0.077 D 1974 .1...-7

6 ,F 0

6 293,000 0.115 D i 1978 m'(_f.(0 60 359,000 0.154 D , 1972

.7.<

i a 0

385,900 0.192 D 1976 -;-7/0 0 0 0 391,000 0.231 D 1967 770,2_.6 c). 0 393,400 0.269 D 1989 :c g,

a 0

393,700 0.308 A , 1990 z•c./ ?A) o 409,200 0.346 • A 1988

e7,7 '0 0 0

443,600 0.385 A i 1975 iil9 , 1, a 0 455,000 . 0.423 A . 1966

.-3 q

co p 461,000 0.462 A , 1969 ii3L/ -1- o 6 500,300 0.500 A 1968 zfw qo 0 500,500 0.538 A 1971 q q, if 501,000 0.577 A 1979 5/7 3 b o 532,100 0.615 A i 1982 Iti 2, / / 0 564,300 0.654 A 1973 66-7 go, 1,, 594,600 0.692 A 1986 of go 0 692,000 0.731 W 1970

G 3,

,74,

0

699,800 , 0.769 W 1980 7/6 V, 708,400 0.810 W , 1987

-71)

o

0 789,800 0.846 W i 1983

c46

/ ?-0

812,300 • 0.885 W , 1985 _{(--( q} Cp-/ 914,800 0.923 W • 1984

q/,3 _ 77

0

927,100 0.962 W ,

Exchanges

Like diversions in the prior-appropriation system, the right to exchange on the Arkansas River is regulated

by decree. An exchange consists of a water user diverting water at an upstream location on the river and

(26)

Chapter 4 _{Historical Flows and Exchanges}

replacing the diverted water with an equal amount at a downstream location. The distance between the diversion and replacement points can range from a few miles to a hundred miles or more. Exchanges are

usually executed to take advantage of _{upper basin storage facilities and to efficiently manage reusable water}

in a water supply system. Finally, exchange operations must not injure diversions or storage under senior water rights in the river system.

Reusable Water

Water that can be used to extinction, i.e., completely consumed, is called reusable water. Water that is diverted from the west slope to the east slope (transmountain) is one example of reusable water. Fry-Ark Project water diverted through the Boustead Tunnel is reusable water, but rights to reuse this water must

be obtained from SECWCD. _{Water converted from other uses to municipal or industrial use may also be}

reusable pursuant to the terms and conditions of the transfer decree.

The City of Colorado Springs owns several sources of reusable water. Reusable return flows accrue to

Fountain Creek _{from both the City's wastewater facilities and from non-sewered (irrigation) sources. The}

quantity, timing and location have been determined in 84-CW-202, 84-CW-203, 86-CW-118, and 89-CW-36.

Chapter 5 _{discusses the current and projected population and demand data for the City's water utility and}

reusable return flows.

Colorado Springs Utilities staff have projected the reusable return flows from the wastewater treatment plant and the amount of reusable water at the confluence of Fountain Creek and the Arkansas River for

the years 1993, 2012 and 2042. _{These data are presented in detail in Table 5.1,5.2 and 5.3. All return flows}

were assessed transit losses consistent with the use of the Fountain Creek transit loss model currently used

by the Division 2 Engineer.

The City operates local exchanges to allow diversion in Fountain Creek and its tributaries when its local rights to divert water to the water treatment plants are out of priority. The City also operates exchanges for water on the Arkansas River with reusable return flows from the City.

Exchange Data and ARKEX

The Arkansas River Exchange model (ARICEX) _{was developed for the City to calculate the exchange}

potential for the Arkansas River. The exchange potential is defined as the amount of water in the river between the point of upstream diversion and downstream replacement that exceeds any required flow and/or senior diversion requirements within the reach. Because the exchange potential depends on streamflow and daily diversions, it may vary on a daily basis. Using historical gage records, ARICEX calculates the exchange potential between any two points on the mainstream of the Arkansas River between Leadville and Las Animas. Results are computed in cubic feet per second over a 24-hour period (cfsd).

(27)

Chapter 4 Historical Flows and Exchanges

Changes in gage location, installation and termination of gaging stations, and unavailable or lost gage records results in some incomplete data for the 91 data sets that make up the exchange model's 25 years of record. However, because of the logic incorporated into the ARKEX model, missing data is not considered significant in the calculation of the exchange potential. Missing inflow data reduces the calculated exchange potential by understating the amount of water in the stream, while missing diversion data increases the calculated exchange potential by leaving water in the stream that was historically taken out. These missing inflows and diversions affect the exchange potential between the point of the inflow or diversion and the next mainstream gage, where they are accounted for as unmeasured gains or losses.

ARKEX _{compensates for missing data by omitting these nodes from the computation during that specific}

day. Thus, the results of ARKEX _{understate the exchange potential that would have been available.}

Flow data for the Arkansas River basin was collected from six basic sources:

Stream gage data came from USGS and the Colorado State Engineer's Office; Transmountain tunnel flows were obtained from the State and the USBR;

Diversion records came from the State Engineer's Office Annual Water Diversion Report; Minimum streamflows are from stipulations to water court decrees of record;

City of Colorado Springs records;

The remaining points in the model were either calculated from records of water users or estimated from other records using a regression analysis.

In addition to Colorado Springs, Pueblo, the Colorado Canal Companies, and Aurora have also obtained

decrees for certain priorities to exchange when water is available in the river. Table 4.2 lists the decreed amounts of water for each entity, and the amounts assumed for modeling purposes. Once the total exchange potential is calculated for the reach of the river under examination, the senior exchanges that operate in the reach are subtracted from it. Because all senior decreed amounts will not likely be operated simultaneously in the future, several of the competing exchanges were adjusted for modeling purposes as shown in Table 4.2.

Figure 4.1 displays the exchange data from Table 4.2. It illustrates how the City of Colorado Springs' exchanges will likely be used in the future, with and without the construction of a terminal storage reservoir, and the seniority of these exchanges relative to other exchanges on the river. For example, the

left column shows the seniority of the Colorado Springs' _{exchange priorities for the month of October. The}

first 50 cfs of an 84 cfs exchange is satisfied by the 5th exchange priority and the remaining 34 cfs is available from part of the 7th priority. The right column shows the seniority of the City's exchange potential for release rates of 1000 cfs from a terminal storage reservoir. If there is sufficient flow, 50 cfs

will come from the 5th exchange priority, 50 _{cfs from the 7th priority, 400 cfs from the first part of the 8th}

priority and 500 cfs from the remaining part of the 8th priority. Thus, a streamflow of 1540 cfs in October

will allow the City to exchange at a flow rate of 1000 cfs. These figures demonstrate that the exchange potential used in the modeling is conservative because it assumes that all the senior exchanges modeled

(28)

UN MINI NM Mill MIS NMI IIIII Mill MIN Ell ill 11111 MI MINI MIN 11111 NMI 111111 TABLE 4.2 SENIOR NON -WINTER EXCHANGE INTO PUEBLO RESERVOIR — MARCH 16Th TO NOVEMBER 14TH PRIORI= FOR STORAGE SEASON Stipulated Exchange Seniority (CFS) 1 Projected Operation for Modeling (CFS) Priority Pueblo Colorado Springs

Colorado Canal _Companies

RIG- Aurora Total „ Priority Pueblo Colorado Springs Colorado Canal Companies

RIG -Aurora Total 1 2727 1 27 27 2 -. , 100 127 . ' 2 0 . 27 2 3 50 50 , 227 3 . 0 50 • 77 3 4 50 277 4 ' 50 . 127 5 77 - Pueblo Exchange under #1 and #3 • 277 5 50 177 6 . . , Applicable Maximum Rate of Flow allowed by Decree in 83CW18 ' 6 see' 7 100 - Colorado Springs Exchange under #5 — 7 ' -50 8 1/2 - RIG under #8 1/2 Up to 40 CFS of 1/2, but not to exceed 500 AF annually; thereafter 25% of 1/2 up to an additional 500 AF annually 8 1/2 Remaining exchange potential up to 400 CFS, all remaining above 400

-1/2 Remaining exchange potential up

to 400 CFS 5 0 • 'Stipulation entered in Cases 83CW18, 84CW62, 84CW64, 84CW202, 84CW203, and 86CW118. 2No agricultural exchanges to Pueblo Reservoir have been projected for purpose of analysis in this report. 'No City of Pueblo exchanges above 27 CFS to Pueblo Reservoir have been projected for purposes of analysis in this report. 'As set forth in 83CW18 (CFS) March April May June July Aug Sept Oct 11 19 23 32 32 30 20/25 13 Limited to 8250 AF/yr 5Colorado Canal exchange potential considered conservitve because of limitations placed on the outlet channel were included in the analysis. All senior exchanges projected to be satisfied. PAT ROJECINGEN 2.3\REPORTNTABLE4 2.WP D

(29)

Chapter 4 _{Historical Flows and Exchanges}

Remaining 1040 Daily Exchange Potential (CIS) 240 190 177 -127 77 27 -— October Exchange Potential

For Water Released from WWTP From Fountain Creek to Pueblo Reservoir

(varies from 54 to 91 CFS by month)

US

Colorado

Remaining

1540

500 CFS City of Colorado Springs (Total limited to 1000 CFS

in 84 CW 203)

Remaining Exchonge Potential: Colorado Springs Up to 800 CFS: 1/2 of Exchange Potential to Colorado Springs 1/2 of Exchange Potential to Colorado Canal 50 CFS 13 CFS 50 CFS 50 CFS 50 CFS 27 CFS

City of Colorado Springs RIG (varies by month) City of Colorado Springs Colorado Canal Colorado Canal City of Pueblo

RIG Monthly Exchange Rates in CFS (Table 4.3, Note 3) Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep

13 0 0 0 0 11 19 23 32 32 30 20/25 1040 Doily Exchange Potential (US) 240 -190 177 127 -77 27 -October Exchange Potential For Water Released from Storage From Fountain Creek to Pueblo Reservoir

(up to 1000 CFS)

City of Colorado Springs Estimated 2042 Exchange Rates in CFS

At the Confluence, for Direct Release from the Wastewater Treatment Plant Oct Nov Dec Jon Feb Mar Apr May Jun Jul .Aug Sep

84 85 87 86 91 85 78 54 57 64 76 81

Figure 4.1. City of Colorado Springs' Stipulated Exchanges

(30)

1

Chapter 4 Historical Flows and Exchanges

will operate continuously. All exchanges are also calculated on a daily basis in order to ensure that no impacts to senior water rights will occur. This report assumes that exchanges are assumed to be 100% no

exchange opportunity was lost due to mechanical failure, administrative restrictions, or human negligence.

During the Winter Water Storage Season (November 15th through March 15th) Colorado Springs operates

an instantaneous exchange from the confluence of Fountain Creek and the Arkansas River to Pueblo Reservoir. In accordance with the Winter Water Storage Stipulation dated December 28, 1984, Colorado

Springs has an equal priority of _{exchange into Pueblo Reservoir with the Winter Water Storage Program}

participants. The City of Colorado Springs may exchange water from Fountain Creek to Pueblo Reservoir

at a flow rate of up to half of the native inflow into Pueblo Reservoir. The exchange is limited to 17,000 af each winter season. In accordance with the Stipulation, the model limits the amount exchanged to the

minimum of 1) the amount of reusable water discharged from Fountain Creek into the Arkansas, 2) half

of the native inflow into Pueblo Reservoir, or 3) a maximum of 17,000 acre-feet per winter water season.

The amount of _{divertable native flow above Pueblo Reservoir during the winter storage season is shown}

in Tables 4.3 and 4.4. Table 4.3 was used for Scenarios 1 and 2 and Table 4.4 was used for Scenario 3.

While the Winter Water Storage Stipulation does not expressly provide for exchanges by the City above Pueblo Reservoir during the Winter Water Storage season, this report assumes that exchanges to the Otero

Pump Station or other upstream storage facilities could be operated consistently with the Winter Storage

Stipulation and without injury to the Winter Storage Program. However, the City acknowledges that any. such changes in operations may require changes in the Winter Storage Decree, the Winter Water Storage Stipulation, or other legal approvals.

To determine the native water available during the winter water season, the estimated native inflow to

Pueblo Reservoir was obtained from the USBR for the 25-year study period (Table A.9). These flows were

reduced by half, and then accrued in Pueblo at the projected rate that reusable water is expected to flow into the Arkansas River in the year 2042. This inflow schedule was used as the native water available at both Pueblo Reservoir and at the Elephant Rock diversion sites. Because of the lack of storage, the Mt. Princeton diversions were also limited to the projected flow of the future delivery pipeline (41.2 cfs).

Stream Flow Requirements

Exchanges projected for this report are not executed at flows which would reduce the minimum streamflow requirements at both the Fremont County and the Salida wastewater treatment plants in accordance with the City's Arkansas River Exchange Decree. In addition to the above stipulated minimum stream flows, the U.S. Bureau of Reclamation has agreed to augment streamflows on the Arkansas. Each year since

1990, the Bureau has agreed to maintain, to the best of its ability, a year-round flow of at least 250 cfs, and

a flow of 750 cfs from July 15th through August 15th, measured at the Wellsville Gage. The transfer of water from Twin Lakes and Turquoise Reservoirs to Pueblo Reservoir often assures the flow in the river

(31)

=II

.

NMI

-MIN

MIN

NM

NMI

MIN

NIB

111111

11111111

1111

MIMI

1111111

INS

NMI

TABLE 4.3 DIVERTABLE NATIVE FLOW ABOVE PUEBLO RESERVOIR DURING THE WINTER STORAGE SEASON NATIVE FLOW INTO PUEBLO RESERVOIR AS CALCULATED BY THE USBR FOR THE FRY -ARK OPERATIONS MODEL(FAOP) ON A DAILY BASIS, THE NATIVE INFLOW WAS DIVIDED IN HALF, THEN REDUCED TO THE RATE AT WHICH REUSABLE WATER REACHES THE ARKANSAS RIVER. THESE WERE THEN LIMITED TO 17,000 AF DURING THE WINTER STORAGE SEASON. THESE DAILY FLOWS WERE ACCUMULATED IN PUEBLO RESERVOIR. MONTHLY TOTALS ARE SHOWN BELOW. THESE NATIVE FLOWS WERE USED FOR SCENARIOS WATER ACRE*FEET YEAR OCT NOV DEC JAN FEB MAR 1 AND 2 APR MAY JUN JUL AUG SEP TOTAL 1966 0 2522 5354 5280 3845 0 0 0 0 0 0 0 17,000 1967 0 2522 5354 5280 3845 0 0 0 0 0 0 0 17,000 1968 0 2522 5354 5280 3845 0 0 0 0 0 0 0 17,000 1969 0 2522 5354 5280 3845 0 0 0 0 0 0 0 17,000 1970 0 2522 5354 5280 3845 0 0 0 0 0 0 0 17,000 1971 0 2522 5354 5280 3845 0 0 0 0 0 0 0 17,000 1972 0 2522 5354 5280 3845 0 0 0 0 0 0 0 17,000 1973 0 2522 5354 5280 3845 0 0 0 0 0 0 0 17,000 1974 0 2522 5354 5280 2750 1095 0 0 0 0 0 0 17,000 1975 0 2522 5354 5280 3845 0 0 0 0 0 0 0 17,000 1976 0 2522 5354 5280 3845 0 0 0 0 0 0 0 17,000 1977 0 2522 5354 5280 3845 0 0 0 0 0 0 0 17,000 1978 0 2150 4650 5280 4920 0 0 0 0 0 0 0 17,000 1979 0 2200 5354 5280 4166 0 0 0 0 0 0 0 17,000 1980 0 2522 5354 5280 3845 0 0 0 0 0 0 0 17,000 1981 0 2522 5354 5280 3845 0 0 0 0 0 0 0 17,000 1982 0 2522 5354 5280 3845 0 0 0 0 0 0 0 17,000 1983 0 2522 5354 5280 3845 0 0 0 0 0 0 0 17,000 1984 0 2522 5354 5280 3845 0 0 0 0 0 0 0 17,000 1985 0 2522 5354 5280 3845 0 0 0 0 0 0 0 17,000 1986 0 2522 5354 5280 3845 0 0 0 0 0 0 0 17,000 1987 0 2522 5354 5280 3845 0 0 0 0 0 0 0 17,000 1988 0 2522 5354 5280 3845 0 0 0 0 0 0 0 17,000 1989 0 2522 5354 5280 3845 0 0 0 0 0 0 0 17,000 1990 0 2522 5354 5280 3845 0 0 0 0 0 0 0 17,000 MEAN 0 2494 5326 5280 3900 0 0 0 0 0 0 0 17,000 PAPROJECII GEC1323 NODSI M‘SC END 1 \RUNA \NA TV_A RK. WPD

(32)

NMI

MIN

ill

ION

MIN

ME

MIN

MIS

IIIIII

IIIII

NM

INN

SIM

INN

NMI

MIN

11111

MI

TABLE 4.4 DIVERTABLE NATIVE WINTER WATER FLOW AT MT PRINCETON NATIVE FLOW INTO PUEBLO RESERVOIR AS CALCULATED BY THE USBR FOR THE FRY -ARK OPERATIONS MODEL (FAOP) FLOWS INTO PUEBLO ARE ASSUMED TO BE AVAILABLE AT DIVERSION POINTS UPSTREAM FROM PUEBLO RESERVOIR DIVERTABLE NATIVE WATER IN THE WINTER STORAGE SEASON IS LIMITED TO THE LEAST OF 1) THE AVAILABILITY OF NATIVE WATER, 2) REUSABLE RETURN FLOWS, AND 3) THE CAPACITY OF THE MOSQUITO RANGE PIPELINE. THESE NATIVE FLOWS WERE USED FOR SCENARIO 3 WATER ACRE-FEET YEAR OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP TOTAL 1966 0 1226 2533 2533 2287 1267 0 0 0 0 0 0 9,845 1967 0 1226 2533 2533 2287 1267 0 0 0 0 0 0 9,845 1968 0 1226 2533 2533 2287 1267 0 0 0 0 0 0 9,845 1969 0 1226 2533 2533 2287 1267 0 0 0 0 0 0 9,845 1970 0 1226 2533 2533 2287 1267 0 0 0 0 0 0 9,845 1971 0 1226 2533 2533 2287 1267 0 0 0 0 0 0 9,845 1972 0 1226 2533 2533 2287 1267 0 0 0 0 0 0 9,845 1973 0 1226 2533 2533 2287 1267 0 0 0 0 0 0 9,845 1974 0 1226 2533 2533 2287 1267 0 0 0 0 0 0 9,845 1975 0 1226 2533 2533 2287 1267 0 0 0 0 0 0 9,845 1976 0 1226 2533 2533 2287 1267 0 0 0 0 0 0 9,845 1977 0 1226 2533 2533 2287 1267 0 0 0 0 0 0 9,845 1978 0 1226 2533 2533 2287 1267 0 0 0 0 0 0 9,845 1979 0 1226 2533 2533 2287 1267 0 0 0 0 0 0 9,845 1980 0 1226 2533 2533 2287 1267 0 0 0 0 0 0 9,845 1981 0 1226 2533 2533 2287 1267 0 0 0 0 0 0 9,845 1982 0 1226 2533 2533 2287 1267 0 0 0 0 0 0 9,845 1983 0 1226 2533 2533 2287 1267 0 0 0 0 0 0 9,845 1984 0 1226 2533 2533 2287 1267 0 0 0 0 0 0 9,845 1985 0 1226 2533 2533 2287 1267 0 0 0 0 0 0 9,845 1986 0 1226 2533 2533 2287 1267 0 0 0 0 0 0 9,845 1987 0 1226 2533 2533 2287 1267 0 0 0 0 0 0 9,845 1988 0 1226 2533 2533 2287 1267 0 0 0 0 0 0 9,845 1989 0 1226 2533 2533 2287 1267 0 0 0 0 0 0 9,845 1990 0 1226 2533 2533 2287 1267 0 0 0 0 0 0 9,845 MEAN 0 1226 2533 2533 2287 1267 0 0 0 0 0 0 9,845 FROM P:\PROJECT\GEC\323\MODSIM\NATV_ARK.WQ! PAPROJECIAGEC\323\MODSIKSCENE#3\RUNAWATVARK3.WPD

(33)

Chapter 4 _{Historical Flows and Exchanges}

to be well over these levels. As part of the analysis underlying this report, simulations were conducted

which maintained these augmented flows at Wellsville. However, the inclusion of these augmented stream

flows in this study does not indicate any intent of the City to waive any right it may have to object to these releases in the future.

Exchange Potential Data

While ARICEX operates on a daily basis, the model also compiles the daily potential exchanges into

monthly totals. For example, Table 4.7 shows the monthly output from ARICEX. An exchange rate of 250

cfs was selected for release of water from a future terminal storage reservoir on Fountain Creek. The exchange potential output tables are summarized in Table 4.5. Monthly results are presented in Tables 4.6 through 4.11.

Arkansas River Basin raw water storage requirements

1411

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FOR

COLORADO

SPRINGS

UTILITIES

-GE

Gronning

Engineering

Company

RIVER BASIN

STORAGE

EN

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RINGS UTILITIES

EERING COMPANY

Table of

Contents

TABLE

OF

CONTENTS

Table of

Contents

LIST OF

TABLES

Table of

Contents

LIST

OF

FIGURES

Table of

Contents

Executive Summary

ARKANSAS

RIVER BASIN

RAW

WATER

STORAGE

REQUIREMENTS

EXECUTIVE

SUMMARY

Objective ,

City of

Colorado Springs'

Storage Requirements

Executive Summary

Executive Summary

1

1

1

1

1

Fry-Ark Project Storage Space Availability

Executive Summary

1

Chapter 1

Introduction

1

CHAPTER

1:

INTRODUCTION

Project Background and Scope

Chapter 1

Introduction

Project Objectives

Basis of

Raw Water Delivery Alternatives

uonanpo4ui

1

_i

_Introduction

_{Approach to Arkansas Basin Modeling}

_{Approach to Arkansas Basin Modeling}

_{Approach to Arkansas Basin Modeling}

_{Approach to Arkansas Basin Modeling}