OR/14/007 Overview

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Mackay, J D, Jackson, C R, and Wang, L. 2014. AquiMod User Manual (v1.0). Nottingham, UK, British geological Survey. (OR/14/007).

AquiMod is a lumped parameter computer model that has been developed to simulate groundwater level time-series at observation boreholes in aquifers by linking simple hydrological algorithms that model soil drainage, the transfer of water through the unsaturated zone and groundwater flow. It runs on a Windows PC through the command prompt and is configured using a series of text files. The simple structure of AquiMod makes it easy to use in comparison to more complex physically-based distributed models, and therefore should be accessible to those users who are new to the field of groundwater/hydrological modelling. It uses conceptual modelling approaches that are in line with general hydrological process understanding and has been used in the past to teach hydrological modelling concepts to Earth Science undergraduates. The main features of the AquiMod software include:

  • Fast simulation of groundwater level time-series
  • Flexible time-stepping
  • Monte Carlo parameter sampling
  • Modular structure with multiple process representations
  • Choice of objective functions to evaluate model efficiency

Intended use

AquiMod can be applied to any groundwater catchment around an observation borehole with observed groundwater level time-series data. It can be calibrated against these data and used to provide information on the behaviour of groundwater levels beyond observational records. The model has been used in this way for a number of applications, including reconstructing groundwater level records, long term projections of groundwater levels under climate change and forecasting groundwater levels into the near future using meteorological forecasts. Of course, this list of applications is not absolute and users are encouraged to experiment with the software. However, it is important to consider the limitations of the AquiMod when deciding if it is suitable for your intended use. Please refer to a summary of these limitations in (Table 1).

Table 1 Considerations and potential limitations when applying AquiMod for groundwater level simulation.
Consideration Limitation
Lumped model structure AquiMod lumps the catchment area into a single response unit which is characterised by a groundwater level borehole hydrograph. It treats each input variable (e.g. soil type and rainfall) and output variable (e.g. groundwater level) as spatially uniform over your chosen study area and therefore cannot provide information on spatial heterogeneity within a given catchment area.
Time-series data AquiMod needs observed groundwater level time-series to evaluate the model against and corresponding rainfall and potential evapotranspiration (PET) data to drive the model.
Model boundary AquiMod assumes that the groundwater catchment receives recharge from rainfall only, i.e. it does not account for other sources of recharge such as lateral groundwater flows across the catchment boundary.

Generalised structure

AquiMod consists of three modules (Figure 1). The first is a soil water balance module that partitions rainfall between evapotranspiration, runoff and soil drainage. This module simulates the water balance of the root zone, therefore soil drainage is defined as the water that percolates past the root zone and is no longer available for evapotranspiration. Drainage from the soil is then attenuated through an unsaturated zone module which represents percolation to the groundwater table as recharge. This recharge is input to the saturated zone module that simulates aquifer storage and subsequent discharge. It is the saturated zone module that calculates the groundwater level time-series.

Figure 1 Generalised structure of AquiMod.