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Scientific Investigations Report 2008-5079

Prepared in cooperation with Colorado Springs Utilities and the Bureau of Reclamation

Comparisons of Simulated Hydrodynamics and Water Quality for Projected Demands in 2046, Pueblo Reservoir, Southeastern Colorado

By Roderick F. Ortiz, Joel M. Galloway, Lisa D. Miller, and David P. Mau

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Scientific Investigations Report
2008-5079 PDF (6.78 MB)
Abstract

Pueblo Reservoir is one of southeastern Colorado's most valuable water resources. The reservoir provides irrigation, municipal, and industrial water to various entities throughout the region. The reservoir also provides flood control, recreational activities, sport fishing, and wildlife enhancement to the region. The Bureau of Reclamation is working to meet its goal to issue a Final Environmental Impact Statement (EIS) on the Southern Delivery System project (SDS). SDS is a regional water-delivery project that has been proposed to provide a safe, reliable, and sustainable water supply through the foreseeable future (2046) for Colorado Springs, Fountain, Security, and Pueblo West. Discussions with the Bureau of Reclamation and the U.S. Geological Survey led to a cooperative agreement to simulate the hydrodynamics and water quality of Pueblo Reservoir. This work has been completed and described in a previously published report, U.S. Geological Survey Scientific Investigations Report 2008-5056. Additionally, there was a need to make comparisons of simulated hydrodynamics and water quality for projected demands associated with the various EIS alternatives and plans by Pueblo West to discharge treated water into the reservoir. Plans by Pueblo West are fully independent of the SDS project.

This report compares simulated hydrodynamics and water quality for projected demands in Pueblo Reservoir resulting from changes in inflow and water quality entering the reservoir, and from changes to withdrawals from the reservoir as projected for the year 2046. Four of the seven EIS alternatives were selected for scenario simulations. The four U.S. Geological Survey simulation scenarios were the No Action scenario (EIS Alternative 1), the Downstream Diversion scenario (EIS Alternative 2), the Upstream Return-Flow scenario (EIS Alternative 4), and the Upstream Diversion scenario (EIS Alternative 7). Additionally, the results of an Existing Conditions scenario (water years 2000 through 2002) were compared to the No Action scenario (projected demands in 2046) to assess changes in water quality over time. All scenario modeling used an external nutrient-decay model to simulate degradation and assimilation of nutrients along the riverine reach upstream from Pueblo Reservoir.

Reservoir modeling was conducted using the U.S. Army Corps of Engineers CE-QUAL-W2 two-dimensional water-quality model. Lake hydrodynamics, water temperature, dissolved oxygen, dissolved solids, dissolved ammonia, dissolved nitrate, total phosphorus, algal biomass, and total iron were simulated. Two reservoir site locations were selected for comparison. Results of simulations at site 3B were characteristic of a riverine environment in the reservoir while results at site 7B (near the dam) were characteristic of the main body of the reservoir. Simulation results for the epilimnion and hypolimnion at these two sites also were evaluated and compared. The simulation results in the hypolimnion at site 7B were indicative of the water quality leaving the reservoir.

Comparisons of the different scenario results were conducted to assess if substantial differences were observed between selected scenarios. Each of the scenarios was simulated for three contiguous years representing a wet, average, and dry annual hydrologic cycle (water years 2000 through 2002). Additionally, each selected simulation scenario was evaluated for differences in direct- and cumulative-effects on a particular scenario. Direct effects are intended to isolate the future effects of the scenarios. Cumulative effects are intended to evaluate the effects of the scenarios in conjunction with all reasonably foreseeable future activities in the study area.

Comparisons between the direct- and cumulative-effects analyses indicated that there were not large differences in the results between most of the simulation scenarios and, as such, the focus of this report was on results for the direct-effects analysis. Additionally, the differences between simulation results generally were small for the Existing Conditions scenario (water years 2000 through 2002) and the No Action scenario (projected demands in 2046). Finally, comparisons of the simulation results for the No Action scenario to the remaining simulation scenarios (Downstream Diversion, Upstream Return-Flow, and Upstream Diversion) indicated that, in general, the Upstream Diversion scenario was the most similar to the No Action scenario. Conversely, simulated concentrations associated with the Upstream Return-Flow scenario typically were substantially larger than the concentrations for the No Action scenario.

Version 1.0

Posted May 2008


Suggested citation:

Ortiz, R.F., Galloway, J.M., Miller, L.D., and Mau, D.P., 2008, Comparisons of simulated hydrodynamics and water quality for projected demands in 2046, Pueblo Reservoir, southeastern Colorado: U.S. Geological Survey Scientific Investigations Report 2008-5079, 122 p.


Contents

Abstract

Introduction

Purpose and Scope

Acknowledgments

Methods of Hydrodynamic and Water-Quality Simulation

Reservoir Modeling Using CE-QUAL-W2

Streamflow and Water-Quality Modeling for Projected Demands in 2046

Riverine Nutrient-Decay Modeling

Description of Simulation Scenarios

No Action Scenario

Downstream Diversion Scenario

Upstream Return-Flow Scenario

Upstream Diversion Scenario

Existing Conditions Scenario

General Comparisons Between All Simulation Scenarios

Comparison of Results for Selected Simulation Scenarios

Comparison of Existing Conditions Scenario and No Action Scenario

Water-Surface Elevations

Water Temperature

Dissolved Oxygen

Dissolved Solids

Major Nutrients

Dissolved Ammonia

Dissolved Nitrate

Total Phosphorus

Total Iron

Algal Groups and Chlorophyll a

Comparison of No Action Scenario and Other Simulation Scenarios

Water-Surface Elevations

Water Temperature

Dissolved Oxygen

Dissolved Solids

Major Nutrients

Dissolved Ammonia

Dissolved Nitrate

Total Phosphorus

Total Iron

Algal Groups and Chlorophyll a

Summary and Conclusions

References

Appendixes


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