USING TEMPERATURE TO TRACK GROUNDWATER-SURFACE WATER EXCHANGE IN AN URBAN STREAM ALTERED BY HUMAN DEVELOPMENT

This study investigates the impact of urban growth on the exchange of groundwater and surface water in and around streams using temperature data. Urban streams are a complex environment that show qualities of natural streams, as well as the impact of human development. Quantifying these impacts can be difficult without the installation of monitoring equipment. Recent studies show that temperature data could efficiently quantify the impact of urbanization on streams.

Here, we use temperature signals measured in impacted and natural hillslopes to monitor how stream channel connectivity develops during rain events in various conditions at Cooper Creek Experimental Watershed in Cincinnati, Ohio.

The study site is a 200-meter stretch of upper Cooper Creek, a bedrock stream on fractured shale and limestone. The stream banks expose bedrock overlain by construction backfill and floodplain deposits. The stream maintains perennial flow through upstream stormwater infrastructure and exhibits flashy behavior during heavy rain events. An intermittent ~100 m reach occurs where the stream parallels a sanitary sewer line. Historical maps and drawings from this area's development show that the stream channel was moved several meters east of its original path following sewer construction and adjacent grading and backfill during development of a city park.

Thermal imaging and temperature signals from existing piezometers have revealed areas showing a temperature difference caused by the exchange of groundwater and surface water. This evaluation helped locate the best areas for logging temperature data, which establishes flow occurrence, the influence of groundwater and surface water, and, when combined with precipitation data, determines the initiation and duration of additional flow from rain events reaching the stream. Time dependence of these signals is examined through Cross Wavelet Analysis, a tool used to represent the frequency of functions found within a signal bounded in time. This analysis will identify how the timing of different signals correlate and determine the likelihood of them responding to the same forcings.

Comparing the impacted hillslope to the more natural cut-bank downstream will determine the effect of human development on the timing of the exchange between groundwater and surface water.