Impact of Hyporheic Exchange on Stream Temperature in Restored Systems

One of the leading topics of discussion over the years in regard to 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 (Johnson 2004). However, the practice of establishing a riparian community capable of providing significant vegetative shading is expensive and difficult to accomplish in the short term. A possible alternative lies in the practice of enhancing hyporheic connection in restored systems. It has been acknowledged that hyporheic exchange does alter the mechanics of stream temperature regulation (Forney, Soulard, & Chickadel, 2013), 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 resulted in significant improvement of hyporheic connection within the system. Temperature data for 2011 and 2014 (represent pre and post-restoration conditions) was taken from five on site pressure transducers 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. 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 by an average 53% 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.