Project Description:

Streamflow regime is defined as the frequency, magnitude, duration, and timing of surface streamflow presence in a stream network. In headwater stream systems—stream reaches that form the start of river networks—streamflow regimes are highly dynamic, helping to maintain ecosystem function in watersheds. Despite their recognized importance, headwater systems are currently classified as “vulnerable,” meaning that they are particularly susceptible to degradation and alteration. Transportation systems often are the impetus of such vulnerability, especially in urban settings, which results from hydraulic alteration to stream channels, increased runoff from impervious areas, and modification to lateral connectivity of the stream to its hillslopes by the transportation network. The transport of non-point source pollutants is intertwined with and controlled by flow regimes in headwater systems, and is often elevated by urban expansion. A particular pollutant of concern in urban headwater systems is elevated fine sediment levels, which have been recognized as one of the most common nonpoint source pollutants of surface waters in the United States (US EPA).

The overall goal of this project is to investigate how urban landscape disturbance impacts streamflow regime and sediment connectivity in headwater systems by coupling flow state sensing technology, sediment fingerprinting, and model simulations. The project has three primary objectives. The first objective is to quantify the frequency, magnitude, duration, and timing of streamflow regime in urban headwater systems using low-cost flow state data loggers and pressure transducers. The second objective is to utilize sediment fingerprinting methods and end-member unmixing analyses to quantify the contribution of variable landscapes, including landscapes with large degrees of landscape disturbance, to sediment transport in headwater streams. Finally, the third objective is to develop a watershed model to investigate the contribution of headwater streams to watershed sediment budgets. This information will then be leveraged to assess the impact of landscape disturbance on streamflow regime and sediment transport in urban headwater systems. This addresses a need to quantify streamflow permanence in headwater systems and the contribution of headwaters to sediment yield in urban watersheds. Simultaneously, the project will advance methods to characterize hydrologic and sediment connectivity in watersheds.

The Middle Fork of Beargrass Creek (Fig. 1), located within Louisville, KY, will be the testbed to evaluate the impacts of landscape disturbance on streamflow regime and sediment transport. 84% of the Middle Fork of Beargrass Creek is classified as “developed”, and a federal consent decree to reduce combined sewer overflows in Beargrass Creek is currently enacted. 

US DOT Priorities:

This project directly supports the US DOT strategic goal related to climate and sustainability. Sediment and soil are of the largest stores of carbon on earth, and the process of eroding and transporting sediment and soil can transform stored carbon into carbon dioxide that contributes to climate change. Transportation systems contribute to increased runoff and sediment transport in urban settings due to hydraulic alteration of stream channels, increased runoff from impervious areas, and modification to lateral connectivity of the stream to its hillslopes by the transportation network, thereby increasing rates of sediment transport in the system. By better understanding the specific role of landscape disturbance, such as through the development of transportation networks, on streamflow regimes and sediment transport, we can better design solutions to mitigate its impact.

Outputs:

After the project’s completion, we anticipate the following datasets will be procured: 1) approximately two years of streamflow regime data in several headwater tributaries; 2) approximately two years of sediment fingerprinting data in several headwater tributaries and at the watershed outlet; and 3) data to quantify headwater streamflow regime and sediment transport realized in urban headwaters. The project will result in a minimum of three manuscripts. Manuscript 1: which details the impact of urbanization and land use change on streamflow regime in headwater systems. Manuscript 2: which characterizes sediment transport and sediment sources in headwater systems impacted by urbanization and land use change. Manuscript 3: which investigates the controls of streamflow regime and sediment transport in headwater systems as well as the impact of landscape disturbance on streamflow regime and sediment transport in headwater systems. 

Outcomes/Impacts: 

This proposal emphasizes the critical and timely importance of an improved understanding of the functioning of streamflow permanence and sediment transport in urban headwater systems given that: 1) biodiversity in Kentucky (and throughout the US) is reliant upon high-quality streamflow in headwater systems; 2) such streams are at increased risk of degradation and water quality impairment from urbanization and climate change, and  3) the protection of headwater streams is now reduced under the Clean Water Act after recent changes to the WOTUS rule described by the US Supreme Court. Specifically, results of this study could have timely implications for regulatory agencies who have been tasked with redefining WOTUS (i.e., the US EPA and the USACE). An improved understanding of the functioning of headwater systems is expected to better inform such policy.

Additionally, the proposed project offers several opportunities for undergraduate and graduate students to receive training on use of state-of-the-art and novel technologies to monitor and model streamflow and sediment transport. Students involved in this project will be on the forefront of developing methods to evaluate spatially distributed hydrologic models and will receive advanced training in use of water quality sensing technology, sediment fingerprinting, and model application. Such skills may serve students well as consultants and governmental agencies begin adopting such technologies. 

We expect that this study will be highly valuable to organizations such as the USEPA and USACE when evaluating improvements in water quality, especially with respect to the currently enacted consent decree in Jefferson County, KY for combined sewer overflows. Furthermore, we expect that our classifications of the provenance of non-point source pollutants will aid in developing future guidelines for the Louisville Metropolitan Sewer District with respect to sedimentation from new developments.