A field and modeling study of nonlinear storage-discharge dynamics for an Alpine headwater catchment

Abstract

A process-based coupled model of surface-subsurface flow is applied to the simulation of nonlinear hydrological dynamics for an experimental mountain headwater catchment in northeastern Italy. The comparison between measured and simulated responses, both distributed (water table and soil moisture) and integrated (streamflow at the outlet), shows that the model satisfactorily reproduces various nonlinear processes, in particular threshold behavior and hysteresis in the catchment storage-discharge relationship. We typically observe a clockwise loop in this relationship, i.e., streamflow response is faster than groundwater and soil moisture response, due to larger time scales for subsurface processes and to soil moisture persistence and redistribution. The model is based on a standard Richards equation representation of integrated saturated-unsaturated-runoff dynamics and needs no ad hoc parameterization (e.g., for macropores, pipe flow, or retention curve hysteresis) to capture observed hysteretic relationships between storage and discharge. Additional numerical experiments are carried out to investigate how heterogeneity (bedrock permeability and the distinction between riparian and hillslope areas) and aquifer thickness and topography affect this nonlinear dynamics. The results show that catchment topography and soil depth exert the main control on the hysteresis and threshold patterns. This is evident from a spatial analysis of streamflow and water table response times to storm events, where the threshold points correspond to changes in terrain slope. These findings are confirmed by a further set of analyses carried out on an idealized v-shaped catchment.

Runoff generation in mountain catchments: long-term hydrological monitoring in the Rio Vauz Catchment, Italy

“…We suppose that before reaching the threshold, only the water table in the riparian zone sustains runoff, and when the threshold is exceeded hillslope subsurface flow starts contributing to stream runoff. These results are consistent with previous research at LCC (Camporese et al, 2014), BCC (Penna et al, 2015) and other mountain catchments (Jencso et al, 2009;Detty and McGuire, 2010a, b). Fractions of time that piezometers were connected to the stream (Fig.…”

“…At LCC, we observed similar hysteretic relations between depth to water table and streamflow. We analyzed and modelled these hysteretic patterns finding that water table on the hillslopes had a slower response than both streamflow and water table in the riparian zone (Camporese et al, 2014). This implies that the water table in the riparian zone becomes active before the water table on the hillslopes, revealing a fundamental role of topography on runoff generation processes.…”

“…The two rocky catchments are very steep and have <1% soil cover (Penna et al, 2017). BCC and LCC are soil-mantled catchments (soil cover >90%) with steep hillslopes, a distinct riparian zone (8.6% of the catchment area in BCC ; 4.4% of the catchment area in LCC, (Camporese et al, 2014) and saturated areas. In the lower part of RVC cambisols with mull are the prevailing soil types, while soil texture is dominated by clay (range of 45-73% in the soil profile) and has a small fraction of silt (16-28%) and sand (3-25%).…”

Spatial organization of groundwater dynamics and streamflow response from different hydropedological units in a montane catchment

“…Groundwater dynamics play an important role in runoff generation and hydrologic connectivity between hillslopes and streams as they exert strong controls on lateral subsurface stormflow (Weiler et al ., ). The connectivity between riparian and upland areas is also important during low flow periods when hillslope GW seepage often maintains high riparian water tables (Camporese et al ., ). In many cases, these spatial connections are time variant (McGlynn et al ., ).…”

Growth of the Decision Tree: Advances in Bottom‐Up Climate Change Risk Management

“…; Camporese et al. ), but are only beginning to be embraced by the community of practitioners of water‐resource system adaptation to climate change (Khan ).…”