Graduate Student Research Projects:

Kyle Hall-MS Student

Low Flow Direct Deposit Study

When developing a bacterial impairment Total Maximum Daily Load (TMDL) in an upland rural watershed, in-stream direct deposition of livestock and wildlife feces is a significant bacteria source. Direct deposition (DD) is often the main bacteria source driving the reductions needed to meet water quality standards. The freshwater bacteria water quality standard in Virginia specifies in-stream concentration limits and includes both an instantaneous or single sample criterion and geometric mean criterion.  A bacterial impairment TMDL must include load reductions sufficient to achieve zero violations of both criteria. This often results in unrealistic and unachievable bacterial load reductions.  This is especially true during dry weather conditions when DD is the only bacteria source. During dry weather conditions, low-order upland streams frequently stop flowing. However, due to limitations in water quality simulation software, the models continue to predict flow when, in fact, either no flow is occurring or only discontinuous flow is occurring. During these ‘low flow’ conditions, even small amounts of bacteria deposited directly in the stream result in predicted bacteria concentrations much higher than what would realistically occur. These erroneously high simulated in-stream bacteria concentrations are translated into the TMDL in the form of bacteria-source load reductions that are much more severe than what is actually needed to improve water quality.

My research will investigate alternative DD simulation methods. The three methods that will be considered in this study are stage cut-off, flow stagnation, and stream reach surface area. The control will be to permit DD in the stream without consideration of the simulated flow (present method without modification).  These methods have all been used by TMDL developers at some point when developing bacteria impairment and there is a need to compare these methods and their relative strengths and weaknesses.

Objectives

The goal of my research is to evaluate the impact of three different ‘low flow’ DD simulation methods on bacteria source reductions.  The following objectives will achieve this goal:

•      Select three upland, rural watersheds that experience ‘low flow’ conditions and have existing bacteria TMDLs.

•      Using the selected watersheds, perform water quality simulations using three different ‘low flow’ DD simulation methods and a control (present method without modification).

•      Determine the relative strengths and weaknesses of ‘low flow’ DD simulation methods and combinations of methods by comparing water quality criteria violation rates predicted by each method.

•      Determine the effect of each ‘low flow’ simulation method and combination of methods on water quality criteria violation rates for increasing magnitudes of DD reductions.