The most critical data needed for a numerical model(MODFLOW)

To run MODFLOW model you have to have the following general information: They might be grouped in to physical and hydrologic.

Physical Framework

  1. Topography
  2. Geology
  3. Types of aquifers
  4. Aquifer thickness and lateral extent
  5. Aquifer boundaries
  6. Lithological variations within the aquifer
  7. Aquifer characteristics

Hydrological Framework

  1. Water table elevation
  2. Type and extent of recharge areas
  3. Rate of recharge
  4. Type and extent of discharge areas
  5. Rate of discharge

The data required for a groundwater flow modelling study under physical framework are:

  • Geologic map and cross section or fence diagram showing the areal and vertical extent and boundaries of the system.
  • Topographic map at a suitable scale showing all surface water bodies and divides. Details of surface drainage system, springs, wetlands and swamps should also be available on map.
  • Land use maps showing agricultural areas.
  • Contour maps showing the elevation of the base of the aquifers and confining beds.
  • Isopach maps showing the thickness of aquifers and confining beds.

These data are used for defining the geometry of the groundwater domain under investigation, including the thickness and areal extent of each hydro stratigraphic unit.

Under the hydrogeological framework, the data requirements for a groundwater flow modelling study are:

  • Water table and potentiometric maps for all aquifers.
  • Hydrographs of groundwater head and surface water levels.
  • Maps and cross-sections showing the hydraulic conductivity and/or transmissivity distribution.
  • Maps and cross-sections showing the storage properties of the aquifers and confining beds.
  • Spatial and temporal distribution of rates of evaporation, groundwater recharge, groundwater pumping etc.
  • Initial Conditions: The initial conditions refer to initial values of elements that may increase or decrease in the course of the time inside the model domain.

In simple term: you need

 Geometry:

  • shape of the model area
  • Elevation of aquifer bottom and top
  • Thickness of the aquifer

Aquifer Parameters

Distributions of Hydraulic conductivity (K), Transmissivity, storage coefficient, specific storage, etc.

Inflows/Outflows

  • Pumping Well location, well discharge/Recharge
  • Groundwater recharge by precipitation
  • Mountain front recharge, if any
  • Boundary flows

Observed heads and discharge:

  • Monitoring well location and piezometer head
  • Spring discharge if any
  • Initial head

During conceptual model preparation: strongly define the following with evidence

MODFLOW time

  • Be sure how many stress periods are you going to use in your study, why?

Boundary conditions

  • Define your study area well and specify the correct hydraulic boundary conditions

BY: Dr.Kedir Mohammed

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