Modeling Pre-Dam Modification Discharge and

Sediment Transport: Snyder Park,

Springfield, Ohio, USA

James A Blumenschein

Department of Geology

Wittenberg University

Springfield, OH 45501-0720

USA

Proposal

Submitted in partial fulfillment towards the requirement of

the Floyd R Nave Endowment Award.

Introduction

The purpose of this study is to model discharge and

sediment transport through a recreational structure in Buck

Creek in order to create a stage-discharge rating curve

upstream of the structure. A stage-discharge rating curve

is a plot of flow stage against discharge (DeGagne et al,

1996). A stage-discharge rating curve is created so that

when coupled with a continuous gauging of a river’s stage,

a corresponding discharge can be approximated. Discharge

data can usually only be retrieved with a wading rod at

moderate flows, due to obvious dangers. A stage-discharge

rating curve can be used to estimate discharges at higher

flows by extrapolation, however, with increasing

uncertainty as discharge increases. Alternatively,

streamflow, in particular higher magnitude floods, can be

modeled through a channel reach model to compare to and/or

validate extrapolations made from lower magnitude events.

Hydrologic Engineering Center River Analysis System

(HEC-RAS) is a computer modeling program that provides one-

dimensional steady flow, unsteady flow, sediment transport,

mobile bed computations and water temperature modeling.

The program utilizes absolute elevation data,

parameterizing a channel’s geometry, and absolute water-

surface elevation data as baseline data to extrapolate its

variety of computations and modeling capabilities by

transitioning baseline data to a stage-discharge rating

curve.

Stage-discharge rating curves give detailed insight in

to the relation between stage or discharge with variables

such as bed geometry, bed stability and flood response

(Bullard et al, 2006). A continuous record of discharge

can aid in estimating the total discharge of a stream

hydrograph to determine sediment or solute load as well as

accumulated annual volumes of water that may pass through a

given stream cross-section of a reach (Clemmens & Wahlin,

2006). Resultant conclusions of stage-discharge studies

can help to determine effects on rivers produced from

measured or modeled climate and land-use change (McMillan

et al, 2010). Change in landuse and/or climate create

changes in both frequency and magnitude of discharge and

impact stream ecology (Doyle et al, 2005). Different

ranges of discharge drive different ecologic processes such

as algal growth, organic matter transport, nutrient

retention and replenishment, macroinvertebrate disturbance,

and habitat availability (Doyle et al, 2005).

Changes in frequency and magnitude of observed

discharges can change the slope of a stage-discharge curve,

evident in comparative analyses of two curves; denoting a

change in flow-stage for a given discharge.

Background Information

In 2010, a low-head dam situated in Buck Creek at

Snyder Park was modified and four recreational drop

structures, engineered to create hydraulics for kayaking,

were constructed in its place (figure 1). The change in

the cross-section at the upper most structure (Figure 2)

caused a change in the stage-discharge rating curve (Figure

3). Ten field discharge measurements were taken from April

through October of 2010, after completion of the waterway

structures, and characterize discharges from 38 to 335 cfs.

These measurements were taken as a part of a study

conducted by Wittenberg University to quantify the changes

in Buck Creek’s stage-discharge relationship resulting from

the low-head dam removal/modification. The goal of this

study is to use a computer model to extend the post-dam

modification, stage-discharge rating curve for Buck Creek

to include higher discharges.

Study Reach

The Buck Creek study reach starts at Plum Street and

is approximately 0.5 miles in length. The study reach ends

just after four recreational, waterway structures that were

constructed after the removal of a low-head dam in 2010

(figure 1). This straightened and channelized reach

contains a gauging station immediately downstream of Plum

Street, along the north bank (Figure 1). The gauge records

stage at fifteen-minute intervals. The width of the

channel varies from approximately 80 feet to 110 feet with

an average stage of 3.7 feet.

Methods

Baseline data will be collected through the use of a

TopCon GRS-1 GPS unit. The GRS-1 is a survey grade unit

that uses an integrated cellular modem and GNSS satellite

receiver, utilizing both GPS and Glonass satellite systems

to record elevation and position data with, when used with

an L1 antenna, sub-meter accuracy. Using the GRS-1 unit,

cross-sectional surveys will be performed throughout the

length of the study reach, with frequencies of every 50 to

80 feet. More drastic changes in the channel geometry may

call for increased frequencies of surveyed cross-sections.

The GPS unit will also be implemented in attaining

absolute water-surface elevation data. The HEC-RAS

requires the water-surface elevations be given for the

beginning and end of the study reach along with the

elevation’s corresponding discharge. Discharge

measurements will be taken using a Sontek Flowtracker. The

Flowtracker is a handheld Acoustic Doppler Velocimeter

(ADV) that attaches to a wading rod. It measures discharge

using an automatic discharge computation feature that

adheres to United States Geologic Survey and International

Standards Organization standards. It features an internal

quality control that checks for irregularities in both the

data collected and internal workings of the instrument.

The wading rod used in conjunction with the Flowtracker is

a 4-foot, top setting rod.

This baseline data will be tied to real-time stage

data that is collected by the gauging station, located

within the study reach, linking a gauge reading with an

absolute water-surface elevation and discharge value. The

step-back water method will then be used to extend the

post-dam modification stage-discharge rating curve for Buck

Creek. This method uses water surface profiles with

corresponding discharges and channel geometry to create a

stage-discharge rating curve (Kennedy, 1984). HEC-RAS will

be used to complete the step-backwater method, using the

baseline data by extrapolating multiple water surface

profiles with their corresponding discharge values. A

steady-state, stage-discharge rating curve is then

compiled.

Uncertainty with the model is largely dependent on the

number and range of known water surface elevations and

their corresponding discharge values. With numerous,

widely ranging known values, HEC-RAS’s extrapolations are

more constrained and less uncertain. The model generated

by HEC-RAS can be evaluated through the input of known

stage-discharge values. This method is optimally used when

controls other than channel geometry are present, including

in-line wiers, waterway structures, and dams (Kennedy,

1984).

Objectives

Establish absolute elevations for the gauging station

on Buck Creek.

Collect and integrate cross-sectional survey data

throughout the Buck Creek study reach

Collect water surface elevation and discharge data for

a variety of stages on Buck Creek

Create a functional, stage-discharge rating curve for

Buck Creek

Equipment

TopCon GRS-1 GPS Unit with L1 antenna

Sontech Flowtracker and top-setting wading rod

PC desktop or Laptop

Other miscellaneous items

Timeframe

Baseline data will be collected from week 1 to week 4 of

this project’s initialization. Water surface elevations

and discharge values can be collected independently of

cross-sectional elevations. After week 3 or when

sufficient baseline data exists, values can be inputted

into the HEC-RAS program and a stage-discharge rating curve

can be created. Additional water-surface elevations and

discharge values can be added after the generation of the

stage-discharge rating curve. Total estimated time to

completion, 8 to 10 weeks.

Proposed Budget

Much of the equipment to be used in this study is

provided for by the Geology Department of Wittenberg

University. This equipment includes the GRS-1 GPS unit,

the Sontech ADV Flowtracker, and much of the miscellaneous

items. The study reach is within 1 mile of Wittenberg

University, making travel expense, such as gasoline,

negligible.

Figures

Figure 1 – Arial view of Buck Creek at Snyder Park, Springfield, OH. The red contoured line

represents the extent of the study reach. Note the gauging station location immediately

downstream of Plum Street. Flow is to the west.

Figure 2 – Diagram depicting the general change in the geometry of the cross-section at the top of the initial

drop structure.

Figure 3 - Plot of the original stage-discharge rating curve created by the USGS at the Plum Street gauge and the post-

modification stage-discharge rating curve created by Wittenberg University in 2010.

References

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DeGagne, M., Douglas, G., Hudson, H., & Simonovic, S.,

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