Search

Flows of water and sediment on Earth and other planets have a remarkable tendency to organize into channels across environments and scales. Channels are the primary conveyors of water, sediment, and nutrients through landscapes, and despite their prevalence, prediction of channel initiation and organization remains elusive. Models can predict channel initiation on steep hillslopes, but it is unclear how channelization arises on low-gradient floodplains. Here, we show that, in contrast to channelization on hillslopes, floodplains become channelized by headcutting at low specific discharges and moderate slopes (10-4 to 10-3 degrees). Using simplified numerical modeling of a floodplain with homogeneous soil, we show this difference arises because low specific discharge and moderate slopes maximize water drawdown at topographic discontinuities. Field data are consistent with model results and show that low specific discharges and moderate slopes are necessary, but not sufficient, conditions for channelization on floodplains in Indiana, Unites States. Our results imply that certain floodplains tend to self-channelize, and this increases the frequency of flooding and also enhances hydrological connectivity, which regulates biodiversity and nutrient processing. [ABSTRACT FROM AUTHOR]

River networks modify material transfer from land to ocean. Understanding the factors regulating this function for different gaseous, dissolved, and particulate constituents is critical to quantify the local and global effects of climate and land use change. We propose the River Network Saturation (RNS) concept as a generalization of how river network regulation of material fluxes declines with increasing flows due to imbalances between supply and demand at network scales. River networks have a tendency to become saturated (supply ≫ demand) under higher flow conditions because supplies increase faster than sink processes. However, the flow thresholds under which saturation occurs depends on a variety of factors, including the inherent process rate for a given constituent and the abundance of lentic waters such as lakes, ponds, reservoirs, and fluvial wetlands within the river network. As supply increases, saturation at network scales is initially limited by previously unmet demand in downstream aquatic ecosystems. The RNS concept describes a general tendency of river network function that can be used to compare the fate of different constituents among river networks. New approaches using nested in situ high-frequency sensors and spatially extensive synoptic techniques offer the potential to test the RNS concept in different settings. Better understanding of when and where river networks saturate for different constituents will allow for the extrapolation of aquatic function to broader spatial scales and therefore provide information on the influence of river function on continental element cycles and help identify policy priorities. [ABSTRACT FROM AUTHOR]