Ground Water Issues of the South Platte River Basin. Presented by: James L. Jehn, C.P.G. Jehn Water Consultants, Inc.

Transcription

1 Ground Water Issues of the South Platte River Basin Presented by: James L. Jehn, C.P.G. Jehn Water Consultants, Inc.

2 Ground Water Wells South Platte Alluvial Wells Approx. 10,000 Alluvial Wells in the South Platte Alluvium Approx. 880,000 af/yr pumped for Irrigation Approx. 100,000 af/yr pumped for municipal, domestic, livestock, industrial and commercial Approx. 8 million af of surface water is in storage Data obtained from the CWCB ( Jehn Water Consultants, Inc. 2

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4 Ground Water Modeling SDF Jenkins 1970 Glover AWAS Integrated Decision Support Group (IDS) Colorado State University 1. Schroeder, CDWR, 1987 Analytical Stream Depletion Model 2. IDS modified combines Schroeder model with the SDFView model created by IDS Modflow USGS Jehn Water Consultants, Inc. 4

5 SDF Stream Depletion Factor Prepared by Schneider and Hurr, et.al in 1972 Cooperation between the USGS and CWCB SDF = days for depletion to affect the South Platte River Completed for reach of the South Platte from Denver to eastern State Line Jehn Water Consultants, Inc. 5

6 SDF Contours = Days Hurr & Schneider, 6et.al 1972

7 Glover Methodology Transient Ground Water Hydraulics Robert Glover, 1974 Analytical Steam Depletion Model Dewayne Schroeder State Engineer s Office 1987 Jehn Water Consultants, Inc. 7

8 Glover Parameters Well Distance from River = X (feet) Distance from the well to no flow boundary = B (feet) Distance from no flow boundary to River = W (feet) X + B = W Transmissivity (gpd/ft) Specific Yield (usually 0.20) Partial Stream (stream segments) Infinite Aquifer, Alluvial Aquifer, No Flow Jehn Water Consultants, Inc. 8

9 Glover Limitations The aquifer is assumed to be isotropic, homogeneous, of uniform thickness, and infinite, except were bounded by specific boundaries. The transmissivity is the same everywhere and does not change with time. The water table is initially flat. The water temperature is constant. Water is released instantaneously from storage. The stream is straight, infinite in length, and fully penetrating the aquifer. The pumping rate is constant for any pumping period. The diameter of the well is negligible. If the alluvial aquifer version is chosen, the impermeable boundary is straight, infinite in length and parallel to the stream. If the no flow boundary option is chosen, the impermeable boundary is straight, normal to the stream, and infinite in length away from the stream. 9

10 Available Computer Programs AWAS Alluvial Water Accounting System Developed by the Integrated Decision Support Group at Colorado State University Can use both the Glover Methodology and SDF South Platte alluvial aquifer parameter data available via GIS Jehn Water Consultants, Inc. 10

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14 AWAS Transmissivity Output AWAS Provides three Transmissivity Values 1. Transmissivity at the well location 2. Average Transmissivity along the x line from the well to the river. 3. Harmonic Average along the x line from the well to the river. (Harmonic Mean = reciprocal of the arithmetic mean) Jehn Water Consultants, Inc. 14

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18 Modflow A Modular Three Dimensional Finite Difference Ground Water Flow Model USGS McDonald & Harbaugh, dimensional model Example of some of the Model Parameters and Characteristics: top and bottom aquifer elevations Multi layer capabilities Cell sizes variable Transmissivity (horizontal and vertical) Specific Storage, Specific Yield and Porosity Leakance in a multi layer model River and Stream packages with conductance terms Constant Heads/General Heads Recharge/Evapotranspiration Jehn Water Consultants, Inc. 18

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21 Timing of Depletions Analysis of Stream Depletions and Accretions Jehn Water Consultants, Inc. 21

22 Types of Augmentation Sources Direct Release and Storage Recharge Pits Augmentation Wells Jehn Water Consultants, Inc. 22

23 Projection Tools & Accounting Current requirements in Division 1 Water Court Cases Example of Projection Tool 4 years standard Includes prior year s well depletions and augmentation accretions Example of Accounting Form Jehn Water Consultants, Inc. 23

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