Comparison of hyporheic exchange under covered and uncovered channels based on linked surface and groundwater flow simulations

Hyporheic exchange is an important process upon which stream biogeochemical cycling is dependent. The potential for hyporheic exchange in covered channels (i.e., ice-covered channels, karst conduits, fractures) with permeable sediments has not yet been assessed. We characterize the potential for hyporheic exchange in covered channels using linked turbulent channel flow/groundwater flow simulations. Simulations show that hyporheic exchange occurs in covered channels which have shallower hyporheic zones and larger hyporheic fluxes than equivalent-depth equivalent-discharge uncovered channels. We also analyzed hyporheic exchange for the case of freely floating covers with rough undersides and found that hyporheic exchange decreases with increasing cover roughness which in turn is driven by subdued bed topography, a response to additional resistance due to covers. The results suggest that hyporheic exchange occurs in covered channels and may be just as or perhaps more important to the ecology and biogeochemistry of these channels than to open channel streams.