Modeling temperature, recession curves and event response for two third order eastern Connecticut streams

Date of Completion

January 2007

Keywords

Environmental Sciences|Agriculture, Fisheries and Aquaculture

Degree

Ph.D.

Abstract

Maximum and minimum daily temperatures can affect fish habitat. Therefore, the prediction of temperature changes is needed to assess the impacts of potential watershed management decisions, especially during low-flow periods. In the first part of the research, a physically-based model was developed to predict water temperature changes within reaches of a third-order stream in eastern Connecticut in summer season with shallow baseflow conditions. The dynamic model was developed using STELLA® software to couple the mass and energy balances using a one hour time step. The model was calibrated and tested during the summer low-flow season on the Fenton River which is tributary to Mansfield Hollow Lake. The average baseflow in the Fenton River is less than one cubic meter per second (m3/s). Temperatures and water depth were recorded at one hour intervals during the summer in 2004 and 2005, at various locations along the river to provide data for the model calibration and verification. Streamflow measurements were taken to determine the variation in flow between two test reaches. Model results were tested against observed stream temperatures and also compared with the SSTemp model. Results show that the model can be used for prediction of stream temperature changes due to changes in ground water inflow/outflow and could be used to assess various management scenarios of groundwater extraction. ^ Prediction of recession curves remains an important task for management of diversions or reservoirs that affect flow in streams during low-flow periods. There have been many approaches to baseflow recession applying either power or exponential equations, but there has not been any successful approach to link the parameters of these exponential and power equations such as the turnover time of the groundwater storage with hydrological parameters such as the initial peak discharge before the recession and the recession time. The second part of the research tests a generalized approach to the development of coefficients related with the initial peak discharge before the recession and time of recession in either an exponential or power form of recession equations using records of discharge from the Mount Hope and Fenton Rivers in eastern Connecticut. ^ The third part of the research is related to a different approach for the runoff prediction calculation. Several watershed response functions or "models" such the curve number or the rational method have been developed to predict event runoff and peak discharge for a given storm, often for design purposes. The stream response function approach of Hughes has had a lack of testing in other areas besides South Africa. Hughes method includes the application of a hyperbolic tangent function that link the initial and maximum water depth in the watershed with the amount of runoff in percent of water that the system will deliver to the stream. The test of this approach to Connecticut in this research involved the development of an alternative method to determine the stream response function include parameters such the initial watershed storage and the maximum watershed storage using daily watershed budget. Tests the application of this concept to the Mount Hope River, a small New England stream. The general S-Shaped response shows that individual observed hydrograph can be accurately predicted. However some parameters vary among individual events, requiring calibration. ^

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