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Impact of Hyporheic Exchange on Stream Temperature in Restored Systems

Ethan Bauer, PE
LandStudies, Inc
Lititz, PA

One of the leading topics of discussion over the years regarding stream health and water quality is stream temperature. The common school of thought within the industry is that the best and most effective way to regulate stream temperature is by blocking incident solar radiation via shading by riparian vegetation. There is much evidence to support this practice; it is known that solar radiation is the primary contributor for thermal loading within a stream. However, this practice of establishing a riparian community capable of providing significant vegetative shading has its limitation. A possible alternative lies in the practice of enhancing hyporheic connection in restored systems. It has been acknowledged that hyporheic exchange does have an impact on stream temperature regulation, though its influence is rarely included in temperature analyses. To better understand the impact of hyporheic exchange, pre- and post-restoration stream temperatures were compared for Kurtz Run and its tributary in Lancaster County, Pennsylvania. The floodplain restoration was completed by LandStudies, Inc. in 2012 and created conditions conducive to significant improvement of hyporheic connection within the system. Temperature data for pre- and post-restoration conditions was taken from five on site pressure transducers with integrated temperature probes, and solar radiation data was retrieved from a public NASA database. The daily maximum temperature was then plotted against total daily solar radiation to determine a relationship between these variables. After the completion of both a graphical and statistical analysis of the relationship between the datasets, it was determined that the influence of solar radiation on daily maximum stream temperature was reduced in the restored system. Better understanding of the potential impact of hyporheic exchange on stream temperature could significantly impact dominant restoration practices for both designers and regulators.