GIS for Aquifer Monitoring and Modeling - From Field Surveys to Simulation Models: A case study of Kaluvelly Pondicherry basin, South India4.2. Stream Length The stream length of the drainages in ZSB is varying in each segment order. It is depending on slope, lithology and structural features. Generally stream length of the first segment order is greater than steam length of the second segment order and so on ( Table 1). But it is seen that the length of seventh order stream is lessthan eight order for both the drainage systems ( 1950 and 2001). It is probably because of faulting and folding as field observation suggested. However, the comparison of stream length for two drainage systems depicted from DEMs suggests that drainage length is increased. 4.3. Stream Gradient The zone of rapid rock uplift had a steeper gradient, higher relief, and higher gradient indices (Burbank and Anderson 2001). In order to calculate the stream gradient the Dez river profile was digitally drawn on DEM dated 2001 from Chalanchoolan police station near Brojerd city. The total length of the stream is approximated to 165 km (Fig 5). The profile was divided into three sectors such as 1- high Zagros (Imbricate Zone), 2- folded Zagros and 3- folded Zagros towards Dezful embayment in south of Shahbazan station (Fig 6) and ( Fig 7.-A,B,C ). Steplike river profile of the study area is predicted to approach a graded profile which indicates that area has been tectonically disturbed. Stream gradient indices deduced in each part of the profile, shows variation from 806m to about 142m per kilometer during the geological time scale which means that the river profile is experiencing a regarding stages.  Fig 5. Dez river and structural features on DEM of the study area  Fig 6. Dez river profile with about165km  Fig 7.A Stream-Gradient indices, topography profile High Zagros  Fig 7.B Stream-Gradient indices, topography profile for Folded Zagros  Fig 7.C Stream-Gradient indices, topography profile for ZSB-folded Zagros towards Dezful embayment The high index shows the steeper gradient and high tectonic activities are mainly with thrusting and faulting like Main Zagros Thrust, Hoor thrust, Chamsangar fault, Shahbazan strike slip fault (Fig 8) and Baraftab fault. The Dez river profile indicated that the most active tectonic zone falls in folded Zagros where the stream gradient indices vary from 806m to 165m per kilometer (Fig7.B). It also evaluated that the reduction in gradient towards the Dezful embayment may point towards lesser tectonic activities.  Fig 8. Field photograph showing Shahbazan fault, Dez river follow the fault The different formations dominating various type of rocks like limestone and evaporates in Gachsaran formation, shale of Aghajari formation, marls of Kashkan formation, Cretaceous calcareous in contact of the Imbricate Zone and ZFB with Sanandaj-Sirjan Zone may also approaching graded profile of Dez river during the geological time scale in the study area. For the disturbed rivers profile the high SL values or stream gradient may indicate high tectonic activities. The systematic stream gradient map (Fig.3) of the Zagros Structural Belt in GIS environment was made to interpret tectonic correlation. Hence, it is resulted that the Sanandaj-Sirjan Zone exhibits 0 to 0.441 and has low tectonic activity. It also reveals that the ZFB exhibits 0.441 to 4.268 and has higher tectonic activity than other lithotectonic units in the ZSB. These activities in the Zagros mountains generate terraces. When a river that is flanked by flight of fluvial terraces is also oriented at a high angle to strike-slip fault (Burbank and Anderson 2001), the terraces displayed by the fault provide an excellent record of progressive offsets. These terraces have been seen in the study area by changing in river course on the basis of two DEMs dated 1950 and 2001. Because of changes in river course of the Dez river through time in the ZSB the height of steps between terraces along strike-slip faults is a general guide to correlate terraces. The vertical (dip-slip) displacement along the faults is responsible to river height and variation as well. The Dez river in the ZSB cross an active folds, so fluvial terraces is recorded as progressive displacement. The presence of fault and continuation in tectonic activities, rupture the surface. The growth of the structure itself was tectonically pulsed, such that terraces formed during intervals of reduced deformation rates ( Medwedeff et al. 1992). It is expected that the age and height of the terrace generally correlate with the magnitude of displacement. The field checks show that in the ZSB where the folding and faulting are closely spaced, a single terrace is displaced by several faults. 5. Geological settings Geologically the study area consists of various lithological units, ranging in age from Cretaceous units of in contact with the SSZ in the northeast, dominated by calcareous strata, and sub Recent and Recent units in the ZSB in the southern part of the study area (Pirsateh and Ali, 2005). A generalized stratigraphic column for the Zagros Simple Folded Belt, showing Cretaceous through Miocene strata grouped into four units according to relative resistance to erosion. The area is mostly dominated by calcareous Cretaceous, dolomite, limestone, shale, and marls in north, and evaporates (such as gypsum) and highly cemented conglomerate of the Pliocene Bakhtiari formation in the south. The closure of the Zagros basin during Cretaceous–Miocene time generated diverse styles of folding and faulting. These structures, especially in the ZFB exhibit tight, NW-SE–trending folds with closely spaced fracture systems (e.g., see Fig. 6). These types of geological setting have facilitated severe erosion and the formation of rugged and immature topography and a closed drainage system. 6. Structural and Tectonics Drainage may adjust passively to varying resistance of geologic materials, or it may be actively induced to follow a particular course by tectonism. Examples of the latter include faulting, as in the Shahbazan fault. Growing folds and lineaments have affected drainage in the ZSB. Streams that emerge from mountain fronts onto surrounding plains display a fascinating array of structural and tectonic controls. Where mountain fronts are erosional because of a complex interplay of geomorphic variables, they may develop flanking surfaces of plantation called pediments. Deposition at the mountain front produces alluvial fans and knickpoints ( Pirsasteh, 2004) because of the tremendous increase in width as a stream emerges from a mountain canyon through the geological time scale. Passive adjustment to structure is a quality of nearly all the study areas. Perhaps the most interesting situations, however, are drainage anomalies, where streams cut across structural zones. Some streams appear to take the most difficult routes possible through fold belts. 7. Results and discussion This study begins with topography maps of the area in two dates (1950 and 2001). The drainage networks of the study area of different dates are extracted using DEM in GIS environment. The study reflects changes in geomorphology parameters that lead the analyst to define the tectonic processes in the ZFB. Spatial analysis of DEMs in conjunction with the field observations by GPS and numerical geomorphology in GIS environment provides a mean for characterizing tectonic activity of ZFB in a quantitative way. Using DEMs data (1950 and 2001) and software tools have made the study easy and accessible every where. Under the frame work of GIS analysis of geomorphology spatial data (stream length, stream gradient, number of stream segment) and drainage pattern to derive relationships between tectonics and geomorphology parameters becomes increasingly important. Superposition of the drainage networks ( Fig.9)of the area derived from DEMs shows that the drainages form straight line for 1950 (dated 1950), but in case of drainage network (dated 2001), it is seen that almost changes have been tried to become non-straight line and has lost the previous straight direction line. The analysis of two topography maps in GIS environment suggests that drainage networks are following the slope and structural features in ZFB. Present drainages pattern in the study area is dendritic to sub dendritic and parallel to sub parallel. The comparative study of topography and drainage system dated 1950 with topography and drainage system dated 2001 represents that the drainage patterns has been also subjected to some changes due to tectonic activities. For example the trellis drainage pattern changes to sub-parallel and sub-dendritic pattern. It is seen in Fig 9. The total length of the drainage is 25001.386 km. The spatial analysis in GIS environment calculated the drainage basin to be 8109.680 km2. It is seen that the number of the first order streams segment are increased. Morphometric analysis is also suggested that the second order streams segment derived from DEM (dated 2001) are increased to 7940 ( Table 1). It also shows that length of the first order, second order, third order , forth order, fifth order and sixth order streams obtained from DEM ( dated 2001) is increased as compare to length of the streams in 1950. An interesting result is seen for the length of seventh and eight's drainage segment order. Morphometrically the eight's drainage order should be less than seventh stream order while in the study area it is not seen. This reason indicates that ZFB has also been subjected to tectonic activity from 1950 to 2001. Thus it is called Recent neo-tectonic activities. The pattern of the drainages is also suggests that the area is new and tectonically active. The systematic stream gradient map (Fig 3) of the ZSB in GIS environment was made to interpret tectonic correlation. From the map (Fig 3), it is resulted that the Sanandaj-Sirjan Zone that exhibits 0 to 0.441 has low tectonic activity. High stream gradient values have generally been associated with high rates of tectonic activity. Stream gradient map derived from topography map dated 2001 and 1950 shows variation and changes in stream gradient values. It is seen that stream gradient values derived from DEM (dated 2001) has higher stream gradient values (dated 1950). It also reveals that the ZFB that exhibits 0.441 to 4.268, has higher tectonic activity than other lithotectonic units in the ZFB. These activities in the Zagros mountains have generated terraces. However, increasing in length of the stream, number of the drainage segment order, stream gradient reveals that the area has subjected to tectonic activity during past 51 years.   Fig. 9 Superimposed drainage networks derived from DEM for two dates (1950-2001) south west Iran 8. Conclusions Tectonic activities and rock faulting have great influence on stream gradient and stream length. The strong variation and changes in stream segment order and other geomorphic parameters indicates that tectonic processes and evolution in ZFB ( Table 1). The study shows the evolution of drainages in ZFB as well as its partial correlation with tectonic processes. Utility of DEM and GIS techniques for regional scale tectonic studies has been shown in this paper. With the help of digital terrain data, important morphometric parameters are calculated for interpreting tectonic processes. Both the morphometric parameters of Dez drainage basin in 1950-2001 and stream gradient indices were investigated in detail and found to be in agreement with the existing superimposed drainage basin map. This type of analysis can be used in cross disciplinary study of landslide hazards, earthquake, and geotechnical studies in tectonically active ZFB. Acknowledgement Authors are thankful to authorities of Asman Sanjesh-e-Jonoob research and consulting company authorities for providing facilities. The authors are thankful to Prof. SM.Ramasamy director of remote sensing, University of Bharathidasan, tamilnau, India for his ideas. References:
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