Assessment of Hyporheic Exchange at In-stream Restoration Structures on Savage River, Garrett County, Maryland

Previous studies have shown that in-stream restoration structures alter hyporheic exchange dynamics in restored channels; this study assessed hyporheic exchange at a recently constructed stream reach, including the effects of in-stream restoration structures. Hydrometric and thermal data were collected in the streambed near three restoration structures and at a reference site. The hydrometric data indicated that hyporheic flow paths may not have fully developed in the first 16 months following construction; only one in-stream piezometer was unambiguously hydraulically connected to changes in stream stage. Other hydrometric data revealed possible piezometer installations in low permeability materials, potential hydraulic connections to an adjacent wetland or the pre-restoration channel, and a high degree of heterogeneity in both the subsurface material properties and the hyporheic flow patterns. A heat transport model was used to quantify vertical hyporheic fluxes from diurnal temperature fluctuations upstream and downstream of the restoration structures and at the reference site. Fluxes at the reference site were comparable in magnitude to fluxes in the constructed channel, which contrasts a previous study that found enhanced hyporheic exchange near restoration structures. Unfortunately, the sparse instrumentation network at Savage River did not allow for adequate characterization of hyporheic heterogeneities. Future work should include a denser instrumentation network to better characterize flow pattern heterogeneities as well as thorough characterization of subsurface material properties