Home Articles GIS based groundwater assessment model.

GIS based groundwater assessment model.

S. M. Kharad
Project Leader
[email protected]

K. Srinivas Rao
CAD Engineer
[email protected]

G. S. Rao
Senior Manager
[email protected]

L&T Information Technology Limited
Plot No. EL 200, TTC Electronic Zone, Shil Mahape Road
Navi Mumbai- 400 701

A GWAM-model allows engineers and planners to assess the groundwater more efficiently, accurately and at a faster pace

Water resources assessment of a region involves a detailed study of the surface and sub-surface water. To integrate the entire surface and sub-surface data manually requires huge manpower and time. By adopting a GIS platform the result obtained will be faster and more accurate. Till recently, ground water assessment was based on laboratory investigation, but the advent of Satellite Technology and GIS has made it very easy to integrate various databases.

Groundwater is a most important natural resource required for drinking, irrigation and industrialization. The resource can be optimally used and sustained only when quantity and quality of groundwater is assessed. It has been observed that lack of standardization of methodology in estimating the groundwater and improper tools for handling the same, leads to miscalculation of estimation of groundwater. It is essential to maintain a proper balance between the groundwater quantity and its exploitation. Otherwise it leads to large scale decline of groundwater levels, which ultimately cause a serious problem for sustainable agricultural production. A possible solution for such problems is micro level planning, and use of standard methodology for assessing the groundwater. In recent years micro level planning has gained acceptance, since it can be locally applied and readily managed by self-sufficient rural governance.

Watershed Assesment Approach
In the current development, Ground water assessment is based on the water table fluctuation method and calculated based on the norms recommended by National Groundwater Estimation Committee (GEC). The parameters used include:

  • Normal Monsoon Rainfall data for 20 years
  • Normal Yearly Rainfall data for 20 years
  • Depth to Water table for Pre and Post monsoon water level
  • Specific yield data for the zone of water table (this is expressed as fraction and varies with Geological formation)
  • Geomorphology Map
  • Canal Map
  • Surface Water Irrigation (For Monsoon and Non-Monsoon)
  • Return Seepage from Ground Water Irrigation during Monsoon
  • Surface Reservoir map / Water body map and other conservation structure
  • Well Data
  • Landuse/landcover map
  • Slope map
  • SCS Model (1972) is used for calculating the Rainfall infiltration factor.

Fig. No1. Flow Diagram for Ground Water Assessment Model

Methodology
The database listed above (ie Spatial and Non-Spatial database) is created and imported into ARC/INFO as coverage. The required non-spatial database is attached to respective coverage. The module selects the relevant coverages and calculates the recharge or seepage of individual component/coverages. The module then combines the results of individual components and displays value of Groundwater Balance and the categorization of the watershed. Figure 1 is a schematic representation of the methodology.

GIS Model Interface
GWAM is developed for ARC/INFO 7.0.3 or higher version. The programming languag, Arc Macro Language (AML) is used to develop a customized menu interface specifically designed to allow the user to control the model environment. The interface begins with the Main Menu, which in turn, consists of: DISPLAY, STATISTICS, RESULTS, QUIT and HELP.

GIS Modelling Techniques
Several AML algorithms have been written. ARC/INFO and ARCEDIT have been used in building the model. After the building of coverages the attribute data is attached and statistical analysis is performed on each coverage based on the standard formula. The flow diagram (Fig.1) shows the connectivity of different components. All final values of each coverage are stored as variables and arithmetic operations are performed based on formula. Theisson polygon method is used for computing the average depth to water table for Pre and Post Monsoon.

At this stage a counter check is provided to detect possible errors. The Monsoon RF Recharge is calculated using two methods, as per (a) fluctuation method and (b) Adhoc Norms. The model then checks.

Water resources assessment of a region involves a detailed study of the surface and sub-surface water. To integrate the entire surface and sub-surface data manually requires huge manpower and time. By adopting a GIS platform the result obtained will be faster and more accurate. Till recently, ground water assessment was based on laboratory investigation, but the advent of Satellite Technology and GIS has made it very easy to integrate various databases.

Groundwater is a most important natural resource required for drinking, irrigation and industrialization. The resource can be optimally used and sustained only when quantity and quality of groundwater is assessed. It has been observed that lack of standardization of methodology in estimating the groundwater and improper tools for handling the same, leads to miscalculation of estimation of groundwater. It is essential to maintain a proper balance between the groundwater quantity and its exploitation. Otherwise it leads to large scale decline of groundwater levels, which ultimately cause a serious problem for sustainable agricultural production. A possible solution for such problems is micro level planning, and use of standard methodology for assessing the groundwater. In recent years micro level planning has gained acceptance, since it can be locally applied and readily managed by self-sufficient rural governance.

Model Output
There are several ways to access the model result, including maps and tables. The model has a facility of printing the coverages along with the result display as a pop-up window at the corner of the canvas. The result displayed by the model is a brief summary report in a form of text format.

Conclusions
A GWAM-model allows engineers and planners to assess the ground water more efficiently, accurately and at a faster pace than would be possible using a manual method. The GWAM provides an excellent tool for the regional planners especially those dealing with Land Management or Sustainable development projects and others to determine and rank current area under environmental stress, estimate future impact of land use management decisions and set achievable goals.

The authors do realize that, there is still lot of scope for modification and improvement in the model, in terms of enhancements in its methodology, functionality, features and other tools.