Response time and water origin in a steep nested catchment in the Italian Dolomites

Abstract

In this study, we investigate the surface flow time of rise in response to rainfall and snowmelt events at different spatial scales and the main sources originating channel runoff and spring water in a steep nested headwater catchment (Rio Vauz, Italian Dolomites), characterized by a marked elevation gradient. We monitored precipitation at different elevations and measured water stage/streamflow at the outlet of two rocky subcatchments of the same size, representative of the upper part of the catchment dominated by outcropping bedrock, at the outlet of a soil-mantled and vegetated subcatchment of similar size but different morphology, and at the outlet of the main catchment. Hydrometric data are coupled with stable isotopes and electrical conductivity sampled from different water sources during five years, and used as tracers in end-member mixing analysis, application of two component mixing models and analysis of the slope of the dual-isotope regression line. Results reveal that times of rise are slightly shorter for the two rocky subcatchments, particularly for snowmelt and mixed rainfall/snowmelt events, compared to the soil-mantled catchment and the entire Rio Vauz Catchment. The highly-variable tracer signature of the different water sources reflects the geomorphological and geological complexity of the study area. The principal end-members for channel runoff and spring water are identified in rainfall and snowmelt, which are the dominant water sources in the rocky upper part of the study catchment, and soil water and shallow groundwater, which play a relevant role in originating baseflow and spring water in the soil-mantled and vegetated lower part of the catchment. Particularly, snowmelt contributes up to 64 ± 8% to spring water in the concave upper parts of the catchment and up to 62 ± 11% to channel runoff in the lower part of the catchment. These results offer new experimental evidences on how Dolomitic catchments capture and store rain water and meltwater, releasing it through a complex network of surface and subsurface flow pathways, and allow for the construction of a preliminary conceptual model on water transmission in snowmelt-dominated catchments featuring marked elevation gradients

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

“…9). The mixing space highlighted that the rocky subcatchments were recharged mainly by event-water contribution (i.e., snowmelt), while BCC and lower RVC were characterized by large pre-event water contributions (Penna et al, 2017). Our current results let us suppose that understanding the hydrologic connectivity between the upper and lower catchment is complex and hampered by the presence of different aquifers.…”

“…The geological setting mainly consists of Triassic calcareous rocks with peaks of stratified and structurally deformed dolomite rocks (Bosellini et al, 2003;Doglioni and Carminati, 2008). The complex geomorphology of the area determines the presence of two main superposed carbonate aquifers (corresponding to "Dolomia Principale" and "Dolomia Cassiana" formations; Penna et al, 2017) and minor aquifers formed by scree slopes, alluvial and colluvial deposits.…”

“…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.…”

“…Precipitation is measured by non-heated tipping buckets mainly from May to October at different locations with approximately one rain gauge installed per subcatchment in BCC, ChB and RVC. In addition, these data are compared and integrated with all year round measurements of precipitation (by heated rain gauges) and air temperature taken at two weather stations (about 2.5 km on the East and on the West of RVC) operated by the Agency for Environmental Protection of the Veneto Region (Penna et al, 2017). Water level is currently monitored by pressure transducers at BCC, RVC and ChA, while pressure transducers at the outlets of LCC and ChB were active until autumn 2013 and 2016, respectively.…”

“…Collection of tracer data at different locations of RVC allowed us to compare the tracer signature of stream water across an elevation gradient, and identify the main end-members to stream runoff ( Fig. 9; Penna et al, 2017). While δ 2 H of rocky channel runoff and springs in ChA and ChB had a large variability ranging from the signal of snowmelt and that of rain water, spring and stream water of BCC and lower RVC had a damped variability in isotopic composition and were more similar to groundwater.…”