Are catchments leaky?

Abstract

Catchments, generally understood as the drainage areas of low‐order streams, are often regarded as closed hydrologic entities; that is, precipitation (P) minus evapotranspiration (ET) over a catchment equates stream outflow (Q r). Here, we review evidence that catchments can be leaky due to groundwater outflow or inflow across topographic divides, based on catchment mass balance across a continent and several site‐based studies across the globe. It appears that a catchment is more likely to be leaky with the combination of the following factors: small catchment size, positioned at either the high or low end of a steep regional topographic and climatic gradient, underlain by deep permeable substrates that extend beyond the study catchment, and in drier climate or dry seasons and droughts. Catchment leakage has hydrological, geochemical, and ecological implications. Thus, catchments are best framed as semiclosed hydrologic units perched on top of a larger, regional hydrogeological system with no real boundaries regarding the movement of water and solutes. This article is categorized under: Science of Water > Hydrological Processes Water and Life > Nature of Freshwater Ecosystems

A review of groundwater in high mountain environments

“…Additionally, mountain hydrological studies sometimes assume that all groundwater recharges are returned to a river within the surface watershed. This assumption must be carefully examined as small headwater catchments are more likely than other catchments to be "leaky" in that groundwater export is a non-negligible component of the water balance (Fan, 2019).…”

Moving beyond the catchment scale: Value and opportunities in large‐scale hydrology to understand our changing world

“…Subsurface catchment properties can act as a particularly strong filter on climate variability. Large groundwater systems tend to filter out short‐term variation and instead show more pronounced multi‐annual to decadal‐scale variation (e.g., Cuthbert et al, ; Hanson, Dettinger, & Newhouse, ; Sidibe et al, ), which may also be transferred to or received from areas beyond the catchment boundary (Bouaziz et al, ; Fan, ). In contrast, short‐term (up to interannual) variations tend to be dominant in steep catchments with shallow groundwater systems (Sidibe et al, ) or in catchments with strong subsurface heterogeneity (Hartmann, ).…”

Assessing streamflow sensitivity to precipitation variability in karst-influenced catchments with unclosed water balance

“…In catchment hydrology, topographically delineated catchments represent the common units for studies at catchment scale, e.g., hydrological simulations of the catchment responses (Clark et al, 2017;Kirchner, 2009), drought and flood analyses (Haslinger et al, 2014;Merz & Blöschl, 2005;Tallaksen et al, 2009), sediment production and transport from hillslopes to rivers (Liu et al, 2018;Sherriff et al, 2016;Zuo et al, 2016), and the behavior and fate of nutrients and pollutants (Liu et al, 2019;Van Meter & Basu, 2017;Pullan et al, 2016). However, previous work showed that the water balance of topographic catchments may often not be closed (Fan, 2019;Le Mesnil et al, 2020). This is particularly true for karstic regions where recharge areas are often found to not be equal to the topographic catchment.…”