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GIS for Aquifer Monitoring and Modeling - From Field Surveys to Simulation Models: A case study of Kaluvelly Pondicherry basin, South India


2. Study area
The study area (Fig 1) extends from Dezful in north Khuzestan province to Khorramabad and Doorud-Brojerd in north Lorestan (Lurestan) province. sThese two provinces are most important from geology and geomorphology point of view. It is located in such a way that is belonging to ZSB. Both the provinces have different lithostratigraphy and geomorphological setting. The study area varies in elevation from 142 meters to 4200 meters above Mean Sea Level (MSL). The study area is bounded by Longitude 47 º 58' 1.42'' - 49º 18' 50.63'' E and Latitude 32º 21' 40.94'' – 34º 00 00''. It is covered by digital toposheets of Dezful and Khorramabad blocks from Iranian Surveying Organization (ISO) numbers (5654, 5655, 5656, 5657, 5755, 5756, 5757, 5855, 5856) on scale 1:25000.


Fig.1 Sowing study area Zagros mountains south west Iran


3. Data source and methodology
Topography maps of the study area in scale 1:50000 and 1:25000 of two dates (1950 and 2001 respectively) were used for the study. In order to generate DEM, x,y and z attributes in text format are introduced to Rivertools software. The pixel size of proposed DEM was given on the basis of contour interval as 20 meters to increase accuracy. The methodology consists of two steps: 1- extraction and analysis of Dez basin drainage system based on scale 1:50000 and 1:25000 dated 1950 and 2001 respectively. In the present study drainage maps have been prepared from DEM using toposheets with the help of GIS software. Drainage networks of the study area of 1950 and 2001 are superimposed to emphasis the changes in stream length, number of drainage segment orders and drainages pattern. 2- Dez river profile is also digitally drawn on DEM dated 2001 to calculate the stream gradient. This is done in Rivertools software across to the field observations. This technique allows analysts to point out structural features such as faults and folds. Faults and folds on the DEM are recognized (Fig.5) on the basis of tone, slope, linearity, changes in topography and drainages direction. However, geomorphic signatures and aspects were keys to interpret the tectonic activity in ZFB. Broadly the methodology is defined as follows:

  • The topography map of 1950 is scanned and digitally drawn in the form of vectors and points to define x, y and z attributes using ER-mapper 6.1, Arcview 3.2 and Arcinfo softwares.
  • Vectors are introduced to Microstation J to export into text format
  • Delineation of drainage networks for toposheet dated 1950. Simultaneously, the text formats were introduced to other GIS software called Rivertools 2.4 to create DEM (Fig 2) for analyzing the drainage networks (Fig 3). Morphometry analysis helps analysts to analyze and interpret tectonic geomorphology of the ZFB. Extraction of drainage networks involves three conditioning processes. They are:


    • *Flow grid generation- the objective of the first step in the conditioning phase is to create an adjusted “depression-less” raise to the lowest elevation value on the rim of the depression. Each cell in the depression-less digital elevation data set will then be part of cells leading to an age of the data set. A path is composed of cells that are adjacent horizontally, vertically, or diagonally in the raster (eight-way connectedness) and that steady decrease in value. The purpose of this routine is to extract a flow grid from a DEM grid.

    ** Basin outlet- This is a graphic routine that allows one of specify the basin that one wants to analyze by providing Rivertools with the precise location of the basin’s outlet. In the present study the complete DEM was used. Therefore an outlet was specified in the GIS environment on DEM on the basis of filed observations.

    ***RT Treefile- This routine creates a Rivertools “treefile” for one or more of the basins in the DEM, from a Rivertools flow grid. The treefile is a vector format file, which can store data for many disjoint basins. Every pixel in the particular basin is the outlet pixel for a sub-basin that is contained in that basin.

  • The digital topography map dated 2001 provided by the ISO in scale 1:25000 were converted to text format in the form of x,y and z using Microstation J. X, y and z attributes were introduced to Rivertools software to generate the DEM.
  • Delineation of drainage networks for toposheet dated 2001- the same procedure ( as for toposheet dated 1950) was applied for morphometric analysis and to generate the drainage networks map
  • Visual interpretation of the topography map. Field observations using global positioning system (GPS) to obtain elevation, faults, folds and drainage length. Dez river profile is interpreted (Burbank and Andrson, 2001) to evaluate the structural and tectonic behaviors in ZSB.
  • Superimposing two drainage networks to highlight the changes of the drainages from 1950 to 2001.
  • Finally, the difference between drainage networks dated 1950 and 2001 is interpreted to evaluate tectonic processes in ZFB.

Fig. 2 DEM of the study area


SSZ- Sanandaj Sirjan Zone
MZT-Main Zagros Thrust
HZ- High Zagros


Fig 3. Stream gradient map of the study area derived from topography map dated 2001-ZFB south west Iran


4. Geomorphology and Morphometric Analysis
Tectonic force is an impulsive event that occurs at the beginning of the geomorphic cycle. Subsequently geomorphic process attack and degrade the topography. Since tectonic activities in the area started during Triassic to Late Cretaceous ( Pirasteh and Ali, 2005) then the oldest geomorphic features have formed in the ZFB and resulted the rugged topography. The tectonic activity in ZFB is more than the rate of erosion therefore erosion may change the topography and uplifting ( Ali and Pirasteh 2003 as stream length, stream orders (Tables.1) and drainage patterns are carried out. Drainages in the study area also often shift the direction of flow due to folding, thrusting, and rock type variations as the orogen is exhumed (Fig.4).


Fig.4. Structural Zone and transverse drainage of the Zagros Mountains.
Oberlander (1965).


The influence of topography on drainage morphometry has been well known for decades or even centuries. The idea of behavior on drainage is given in this paper by trying to correlate individual topography morphological attributes and the processes of tectonics and rock faulting. Among morphological attributes, the most important for the study of tectonics are probably stream length, stream gradient and other geomorphic features as pointed out by Burbank and Anderson (2001). Currently, advantages of GIS have allowed many investigators to contrast digital elevation model and extract drainage morphometry attributes in order to study the correlation between topography and drainage morphometric. In this study, we relied on this approach as there are advantages of GIS on how topographic attributes and comparison of two topography maps in different dates can be linked to interpret tectonic processes and tectonic evolution in ZFB. A quantitative, morphometric analysis of a drainage basin of two different dates is considered to be the most satisfactory method to tectonic processes interpretation. It enables us (i) to understand the relationships among different aspects of the drainage pattern of the basin, (ii) to make a comparative evaluation of drainage derived from different topography maps and DEMs (dated 1950 and 2001). The morphometric parameters computed include number of stream segment order, stream gradient, stream length (Table 1) and drainage patterns. The morphological attributes displayed by channel length, stream gradient, etc. at each segment order for morphological evolution.

Geomorphologically the overall drainage pattern of the basin is sub-dendritic indicating the heterogeneity of rocks and gradual slope towards the main stream. At places parallel to sub-parallel, trellis and dendritic type of network is seen.

In order to determine the relationships between tectonic activity and drainage systems or to find the present day morphometric behavior of the study area, the geomorphology parameters are studied.

4.1. Drainage networks
The fluvial dissection of the landscape consists of valleys and their included channel ways organized into a system of connection known as a drainage network. Drainage networks in ZSB display many types of quantitative regularity that are useful in analyzing tectonics evolution. One very useful property is the pattern of dissection. Basically it is summarized the geological significance of various drainage patterns. Dendritic patterns occur in the presence of structural control, as on the ZFB. Areas of trellis and sub parallel drainage include central ZFB and the high Zagros, respectively. An example of drainage pattern is shown in Figure 3.

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