Applications of Integrated Surface Water/Groundwater Modelling - Techniques and
Perspectives
Authors:
P.J. Thompson, M.A. Marchildon, E.J. Wexler, D.C. Kassenaar
Earthfx Inc.
Session: Groundwater-Surface Water Interactions and Ecohydrology
Integrated modelling is emerging as a powerful tool to assess and understand the interactions
between surface water and groundwater processes. This trend is being driven by engineering and
water management challenges such as water budgeting, well permitting, and cumulative impact
assessment that must now consider complex issues such as ecological flow needs under both
drought and high-flow conditions.
The new USGS GSFLOW integrated surface water and groundwater model is an open source code
that is based on the proven PRMS surface water model and the robust, modern MODFLOW-NWT
groundwater model. Hydraulic processes such as reservoir and stream routing are fully simulated,
and lake, stream, and wetland features can interact with multiple components of the groundwater
system. Overland flow is routed to surface water bodies with a cascade approach based on surface
topography while simultaneously, soil-zone interactions are modelled using a soil moisture
accounting scheme coupled to the groundwater system. Importantly, GSFLOW allows the surface
and groundwater sub-models to be built with differing spatial scales. A detailed surface water model
can be coupled to a locally refined groundwater model so that engineering scale problems can be
solved using fast and computationally efficient models.
Traditional un-coupled, steady state modelling approaches often do not provide the necessary scale
needed to offer insight into many surface water/groundwater interactions. For example, vernal pools
fluctuate seasonally both in volume and extent depending on the depth to water table, which in turn
will impact runoff generation; hence, hydrologic interactions can vary not only seasonally or monthly,
but between individual storm events. Transient models are constructed employing hourly
precipitation calibrated to daily targets. Detailed topography and land-use data, distributed NEXRAD
radar precipitation data and a regionally calibrated snowpack model allow processes to be simulated
at a high spatial resolution. Transient, high resolution modelling has required the development of
new software tools to process, visualize, and communicate model results.
Several case studies are presented to demonstrate this modelling approach, including: 1) an
assessment of the impact of a proposed land development on wetlands in a permeable Florida
aquifer system; 2) a catchment-scale water budget simulation of municipal wells located at the base
of a re-entrant valley cut in the Niagara Escarpment with complex lake and wetland interactions; 3)
a comparative analysis of low-impact development (LID) urban design scenarios for the purpose of
groundwater recharge protection, runoff mitigation and preservation of groundwater discharge to
wetlands and streams, and 4) a detailed model of a moraine complex calibrated to assess the
linkages between ecologically significant surface water features and groundwater recharge.
Together, these successful projects illustrate how an integrated model provides the key insight and
understanding needed to assess today’s complex water management challenges.