Improving calibration of groundwater flow models using headwater
streamflow intermittence
Abstract
Non-perennial streams play a crucial role in ecological communities.
However, the key parameters and processes involved in stream
intermittence remain poorly understood. While climate conditions,
geology and land use are well identified, assessing and modeling the
groundwater controls on streamflow intermittence remains a challenge. In
this study, we explore new opportunities to calibrate process-based 3D
groundwater flow models designed to simulate stream intermittence in
groundwater-fed headwaters. Streamflow measurements and stream network
maps are jointly considered to constrain aquifer’s effective hydraulic
properties in hydrogeological models. The simulations were then
validated using visual observations presence/absence of water, provided
by a national monitoring network in France (ONDE). We tested the
methodology on two pilot catchments with unconfined shallow crystalline
aquifer, the Canut and Nançon (Brittany, France). We found that
streamflow and expansion/contraction dynamics of the stream network are
both necessary to calibrate simultaneously hydraulic conductivity K and
porosity θ with low uncertainties. Conversely, calibration resulted in
accurate prediction of stream intermittence - in terms of flow and
spatial extent. For the two catchments studied, the Canut and Nançon,
hydraulic conductivity is close reaching 1.5 x 10 -5
m/s and 4.5 x 10 -5 m/s respectively. However, they
differ more by their storage capacity, with porosity estimated at 0.1 %
and 2.2 % respectively. Lower storage capacities lead to higher
fluctuations in the water table, increasing the proportion of
intermittent streams and reducing perennial flow. This new modeling
framework allowing to predict streamflow intermittence in headwaters can
be deployed to improve our understanding of groundwater controls in
different geomorphological, geological, and climatic contexts. It will
benefit from advances in remote sensing and crowdsourcing approaches
that generate new observed data products with high spatial and temporal
resolution.