Bringing groundwater information to the surface
The eWater CRC team is filling in three model gaps for estimating the interaction between surface-water (SW) and groundwater (GW) near rivers and streams, and how that exchange depends on land and water management.
In a wide-ranging literature review in 2008, the team found that many existing groundwater models are not good at handling the interaction with surface-water. In simple models, the river is just modelled as a boundary. While there are more sophisticated models, they are hampered by lack of data for testing and validating them in Australian river basins, and often they are too complex to run on the computing resources available in groundwater-management offices.
The team’s reach-scale ‘GW-SW Link’ model is designed to bring more intelligent information about groundwater processes into existing river (surface-water) models for regulated river reaches within river valleys. The model estimates the GW-SW interactions as simple volumes gained or lost due to seepage into or out of the river, evaporation, or pumping; and feeds them into each time-step of the river model.
For the smaller scale, the team is building a ‘Floodplain Processes’ model, to simulate the water moving within streambanks, in evapotranspiration, and during recharge from flooding. This model interfaces well with ecological response models. It differs from the reach-scale model in its higher resolution modelling of the detail and timing of water movements, and because it can simulate SW-GW interactions due to overbank flooding as well as from seepage through river banks.
Image: Bores into surface water bodies give access for measuring local groundwater.
And for unregulated upland catchments, the team is adapting concepts from the existing ‘2CSalt’ model of groundwater flow and salt transport so that it interfaces with eWater’s Source Catchments software for modelling catchment runoff and water quality. The adapted model will capture differences in travel time for groundwater, in steep versus shallow slopes or sand versus clay, for example, or because of distance from stream. The groundwater is routed from the ‘recharge areas’ within a catchment through both deep and lateral flow pathways to the stream or river where it is added to the estimates of surface runoff from other modules within Source Catchments.