COMPARISON OF TRANSIENT STORAGE CHARACTERISTICS IN RESTORED AND UNRESTORED REACHES OF THE PROVO RIVER, HEBER VALLEY, UTAH

We performed Rhodamine-WT (RWT) stream tracer tests in order to compare transient storage characteristics between restored and unrestored reaches of the Provo River, Heber Valley, Utah. The 13-mile long section of the Provo River located in the Heber Valley (Middle Provo) has undergone extensive geomorphic and hydrologic alteration during the 20th century due to federal reclamation projects. The Provo River Restoration Project (PRRP) is intended to mitigate the negative environmental impacts of reclamation activities by completely renaturalizing the channel and floodplain. Restored reaches are designed with alternating pool-riffle sequences, mid-channel gravel bars, point bars, secondary channels, and relatively high sinuosities. Unrestored reaches are constrained by dikes, making them relatively straight, topographically homogenous, and providing a narrow distribution of water velocities within the channel. Test reaches in our study were chosen in order to provide a statistically sound basis for determining the general effects of the PRRP in terms of transient storage. In each 500 to 800 meter long reach, a single pulse of RWT was injected at a discharge close to base flow (4 cms). Breakthrough curves were developed using RWT concentrations automatically logged in the field at 5-second intervals. We simulated field data using STAMMT-L software, which solves a one-dimensional advective-dispersive transport equation, accounting for transient storage. Model parameters yielded estimates of the average cross-sectional area of transient storage, and average transient storage residence time in each reach. Results suggest that restoration efforts have produced a relative increase in these aspects of transient storage, indicating a potential increase in hyporheic residence time. We hypothesize that greater geomorphic complexity introduced by channel restoration will increase hyporheic exchange.