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Scientific Investigations Report 2007-5177


Publications Warehouse SIR 2007-5177

Prepared in cooperation with the City of Lincoln, Nebraska, and the Lower Platte South Natural Resources District

An Assessment of Hydrology, Fluvial Geomorphology, and Stream Ecology in the Cardwell Branch Watershed, Nebraska, 2003–04

By David L. Rus, Benjamin J. Dietsch, Brenda K. Woodward, Beth E. Fry, and Richard C. Wilson

SIR 2007-5177 Contents | Citation

Abstract

An assessment of the 16.3-square-mile Cardwell Branch watershed characterized the hydrology, fluvial geomorphology, and stream ecology in 2003–04. The study—performed by the U.S. Geological Survey in cooperation with the City of Lincoln, Nebraska, and the Lower Platte South Natural Resources District—focused on the 7.7-square-mile drainage downstream from Yankee Hill Reservoir.

Hydrologic and hydraulic models were developed using the Hydrologic Modeling System (HEC-HMS) and River Analysis System (HEC-RAS) of the U.S. Army Corps of Engineers Hydraulic Engineering Center. Estimates of streamflow and water-surface elevation were simulated for 24-hour-duration design rainstorms ranging from a 50-percent frequency to a 0.2-percent frequency. An initial HEC-HMS model was developed using the standardized parameter estimation techniques associated with the Soil Conservation Service curve number technique. An adjusted HEC-HMS model also was developed in which parameters were adjusted in order for the model output to better correspond to peak streamflows estimated from regional regression equations. Comparisons of peak streamflow from the two HEC-HMS models indicate that the initial HEC-HMS model may better agree with the regional regression equations for higher frequency storms, and the adjusted HEC-HMS model may perform more closely to regional regression equations for larger, rarer events. However, a lack of observed streamflow data, coupled with conflicting results from regional regression equations and local high-water marks, introduced considerable uncertainty into the model simulations. Using the HEC-RAS model to estimate water-surface elevations associated with the peak streamflow, the adjusted HEC-HMS model produced average increases in water-surface elevation of 0.2, 1.1, and 1.4 feet for the 50-, 1-, and 0.2-percent-frequency rainstorms, respectively, when compared to the initial HEC-HMS model.

Cross-sectional surveys and field assessments conducted between November 2003 and March 2004 indicated that Cardwell Branch and its unnamed tributary appear to be undergoing incision (the process of downcutting) (with three locations showing 2 or more feet of streambed incision since 1978) that is somewhat moderated by the presence of grade controls and vegetation along the channel profile. Although streambank failures were commonly observed, 96 percent of the surveyed cross sections were classified as stable by planar and rotational failure analysis—a disconnect that may have been the result of assumed soil properties. Two process-based classification systems each indicated that the reaches within the study area were incising and widening, and the Rosgen classification system characterized the streams as either type E6 or B6c. E6 channels are hydraulically efficient with low width-depth ratios, low to moderate sinuosity, and gentle to moderately steep slopes. B6c channels typically are incised with low width-depth ratios maintained by riparian vegetation, low bedload transport, and high washload transport. No obvious nickpoints (interruption or break in slope) were observed in the thalweg profile (line of maximum streambed descent), and the most acute incision occurred immediately downstream from bridges and culverts.

Nine water-quality samples were collected between August 2003 and November 2004 near the mouth of the watershed. Sediment-laden rainfall-runoff substantially affected the water quality in Cardwell Branch, leading to greater biochemical and chemical oxygen demands as well as increased concentrations of several nutrient, bacteriological, sediment, and pesticide constituents. The storage of rainfall runoff in Yankee Hill Reservoir may prolong the presence of runoff-related constituents downstream.

Across the study area, there was a lack of habitat availability for aquatic biota because of low dissolved oxygen levels and low streamflows or dry channels. In August 2003, the aquatic community near the mouth of the stream was represented by undernourished fish, pollution-tolerant Dipteran invertebrates, and pollution-tolerant, autotrophic algae. The combined effect of exposure to rainfall-runoff and a lack of available habitat may be contributing to the degraded aquatic communities observed at the monitoring site.

Posted January 2008

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Contents

Abstract

Introduction

Study Area

Purpose and Scope

Methods

Data Compilation

Topographic Surveying and Stream-Channel Characterization

Water-Quality and Ecological Sampling

Existing Spatial Data Sets

Assessment of Hydrology

Hydrologic Simulation

Initial Watershed Parameter Estimation

Adjustment of Watershed Parameters

Regional Regression Equations

Model Adjustment

Hydraulic Simulation

Cross-Sectional Information

Manning’s Roughness Coefficients

Bridges and Culverts

Estimating Peak Streamflow from High-Water Marks

Assessment of Fluvial Geomorphology

Stream-Channel Cross-Sectional Characterization

Channel Geometry

Energy Associated with Bankful Conditions

Channel Classification

Streambank-Stability Analysis

Reach Characterization

Thalweg Profile and Streambed Gradation

Assessment of Stream Ecology

Fish Community Assessment

Aquatic Invertebrate Metrics

Algal Community Metrics

Results of Hydrologic Assessment

Hydrologic Simulations

Regional Regression Equation Results

Initial Model Results

Adjusted Model Results

Comparison to Local High-Water Marks

Hydraulic Simulations

Results of Fluvial-Geomorphic Assessment

Cross-Sectional Characterization

Channel Geometry

Streambank-Stability Assessments

Reach Characterization

Summary of Cross-Sectional Characterizations

Meander Geometry

Thalweg Profiles

Results of Ecological Assessment

Water Quality

Aquatic Biota

Fish

Aquatic Invertebrates

Algal Community

Aquatic Habitat

Summary and Conclusions

References Cited

Appendix 1. Channel geometry characteristics for cross sections between November 2003 and March 2004 in the Cardwell Branch study area

Appendix 2. Field observations and assessments for cross sections surveyed between November 2003 and March 2004 in the Cardwell Branch study area

Appendix 3. Classification of channels in the Cardwell Branch study area

Appendix 4. Meander geometry measured at selected meanders in the Cardwell Branch study area

Appendix 5. Water-quality constituents in samples from Cardwell Branch, Nebraska, 2003–04

Appendix 6. Fish taxa collected at the ecological monitoring site on August 26, 2003, Cardwell Branch, Nebraska

Appendix 7. Aquatic invertebrate taxa collected at the ecological monitoring site on August 26, 2003, Cardwell Branch, Nebraska

Appendix 8. Algal taxa collected at the ecological monitoring site on August 26, 2003, Cardwell Branch, Nebraska

Appendix 9. Potential aquatic habitat observed in the Cardwell Branch study area, 2003–04



Report Citation

Rus, D.L., Dietsch, B.J., Woodward, B.K., Fry, B.E., and Wilson, R.C., 2007, An assessment of hydrology, fluvial geomorphology, and stream ecology in the Cardwell Branch watershed, Nebraska, 2003–04: U.S. Geological Survey Scientific Investigations Report 2007–5177, 70 p.

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