The fan of influence of streams and channel feedbacks to simulated land surface water and carbon dynamics

Abstract

Large-scale land models assume unidirectional land-to-river hydrological interactions, without considering feedbacks between channels and land. Using a tested, physically based model with explicit multiway interactions between overland, channel, wetland, and groundwater flows, we assessed how the representation and properties of channels influence simulated land surface hydrologic, biogeochemical, and ecosystem dynamics. A zone near the channels where various fluxes and states are significantly influenced by the channels, referred to as the fan of influence (FoI) of channels, has been identified. We elucidated two mechanisms inducing the model-derived FoI: the base flow mechanism, in which incised, gaining streams lower the water table and induce more base flow, and the relatively more efficient conveyance of the channel network compared to overland flow. We systematically varied drainage density and grid resolution to quantify the size of the FoI, which is found to span a large fraction of the watershed (25-50%) for hydrologic variables including depth to water table and recharge, etc. The FoI is more pronounced with low-resolution simulations but remains noticeable in hyperresolution (25 m) subbasin simulations. The FoI and the channel influence on basin-average fluxes are also similar in simulations with alternative parameter sets. We found that high-order, entrenched streams cause larger FoI. In addition, removing the simulated channels has disproportionally large influence on modeled wetland areas and inundation duration, which has implications for coupled biogeochemical or ecological modeling. Our results suggest that explicit channel representation provides important feedbacks to land surface dynamics which should be considered in meso or large-scale simulations. Since grid refinement incurs prohibitive computational cost, subgrid channel parameterization has advantages in efficiency over grid-based representations that do not distinguish between overland flow and channel flow.

Seasonal and Interannual Patterns and Controls of Hydrological Fluxes in an Amazon Floodplain Lake With a Surface‐Subsurface Process Model

“…However, when the stage in the streams is higher than land elevation, it will flood the land gridcells. Baseflow is modeled as a head‐dependent first‐order exchange between the groundwater level and the stream stage (Gunduz & Aral, ; Shen et al, ; Shen & Phanikumar, ) and is calculated after each hourly time step. To describe such two‐way interactions, our preprocessing utility records the mapping relations between stream grid cells and land grid cells (Shen et al, ).…”

Geomorphological significance of at‐many‐stations hydraulic geometry

“…Besides their primary utility for streamflow measurements around the world, these relations present tremendous practical significance for myriad applications including routing in hydrologic models [Bieger et al, 2015], geomorphological assessment [Parker et al, 2007], fish habitat [Rosenfeld et al, 2007], and design of channel restoration [Rosgen, 1994;Williams et al, 2002;Shields et al, 2003]. Better channel representation is also important for large-scale land surface hydrologic models [Shen et al, 2013[Shen et al, , 2014[Shen et al, , 2016Clark et al, 2015]. It is well understood that AHG exponents can be determined given site-specific cross-sectional geometry and roughness profile, and both exponents and coefficients are dependent on other AHG parameters in complex ways [Ferguson, 1986].…”

Constraining the annual groundwater contribution to the water balance of an agricultural floodplain using radon: The importance of floods

“…Both surface water and groundwater were highly responsive to rainfall, demonstrating the effective connectivity of the drainage network with the floodplain. A more rapid response in land surface hydrology including shorter lag times is often associated with extensively drained floodplains [ Blann et al ., ; Levavasseur et al ., ; Shen et al ., ]. This effect may also influence near surface groundwater hydrology, where any recharge following rain appears to be offset by groundwater discharge (Figure ).…”

“…Hydrological interactions between streams and the land provide important feedbacks to land surface hydrologic, biogeochemical, and ecosystem dynamics [ Shen et al ., ]. Hydrological flow regimes in floodplains are characterized by base flow, flow pulse (below bankfull), and flood pulse (above bankfull), which can result from different water sources including tributary inflow, overland flow, and groundwater discharge [ Tockner et al ., ].…”