INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 5, No 1, 2014 Copyright by the authors - Licensee IPA- Under Creative Commons license 3.0 Research article ISSN 0976 4402 Manual and automated delineation of watershed boundaries a case study from Kangra region of western Amit Kumar 1, Ravinder Dhiman 2 1. CSIR-Institute of Himalayan Bioresource Technology, Council of Scientific & Industrial Research, Palampur, Himachal Pradesh, India. 2. Institute of Environmental Studies, Kurukshetra University, Kurukshetra, Haryana, India. amitkr@ihbt.res.in doi: 10.6088/ijes.2014050100002 ABSTRACT A study was carried out in Kangra district of Himachal Pradesh in Indian western Himalaya to understand feasibility of automated and manual watershed boundary delineation. It was observed that manual preparation of these boundaries are tedious, time consuming and require base inputs in terms of topographic maps. It is done by skilled user. The automated approach for watershed delineation is simpler as comparison, and can be carried out using open source software and freely available database as inputs. The results showed that the automated watershed boundaries were accurate, smooth and faster in processing. The automated approach is advantageous in mountainous complex terrain drained by numerous smaller tributaries. Keywords: Watershed, Topographic Map, DEM, Manual, Automated, Kangra 1. Introduction A watershed is a natural geo-hydrological unit of land, which collects water and drains it through a common point by a system of streams (Paranjape et al., 1998). It is a natural water divide that separates one drainage basin from other (Soliman et al., 1998). Hence it is globally considered as ideal natural boundary for sustainable development and management of natural resources. The Watershed Boundary Dataset (WBD) is such an example which is collection of hydrologic unit data of United States based on topographic and hydrologic features (WBD, 2012). In India, the concept of watershed as planning unit for development of land and water resources has been widely accepted (Kakade and Hegde, 1998; Singh et al.,2011) and a precise watershed boundary of the region under investigation is prerequisite for such type of planning. The present paper thus aims to demonstrate traditional and modern approaches for delineating watershed boundaries. Traditionally, watershed boundaries are drawn on topographic maps (http://earthsci.org/education/fieldsk/topmap.htm). In such maps, line of water divide or flow direction of water is decided with the help of contours and spot heights as well as drainages depicted on the maps (IMSD, 1995; USDA, 2003). The availability of geo-informatics tools and spatial data has now provided users with opportunities for automated generation of watershed boundary. These modern approaches of watershed delineation require a Digital Elevation Model (DEM) as a base input. The watershed boundary is automatically derived from DEM following various steps such as sink removal, assigning flow direction and calculation of flow accumulation (Savant et al., 2002). Moreover, the global coverage of Received on March 2013 Published on July 2013 16
these DEM are available and can be freely downloaded (http://srtm.csi.cgiar.org/). The various software (Map Window, HecRAS, etc.) required for these analysis are either standalone or are extensions to some existing software. Figure 1: Study area In the light of above background, watershed boundaries of drainages flowing in Kangra district of Himachal Pradesh in India (Figure 1) were delineated using traditional and modern methods. The aim was to understand the efforts involved in watershed boundary delineation in a complex rugged mountainous terrain with DEM having two different resolutions. The study area lies between 31 41 to 32 28 N latitude and 75 35 to 77 04 E longitude and cover 5739 km 2 area. It is a part of Indian western Himalaya with elevation ranging from 248 to 5861 m amsl. The climate of the district varies from sub-tropical in low hills and valleys to sub-humid in the mid hills and temperate in high hills. The average annual rainfall in the district varies from 1500 to 1800 mm. River Beas and its tributaries constitute the main drainage system in Kangra district except for the extreme north-eastern part in Bara Bhangal area, where it forms a part of the river, Ravi. \ 2. Materials and Methods Figure 2: SRTM DEM study area 17
The topographic maps (43 P, 52 D, 44 M and 53 A) on 1:250,000 scales from Survey of India, Dehradun, India were used for manual digitization watershed boundaries using Arc GIS 9.3 (http://www.esri.com). The Map Window 4.8.3 software (http://mapwindow4.codeplex.com) was used for automated delineation of watersheds using CARTOSAT DEM of 30 m resolution from National Remote Sensing Centre (NRSC), Hyderabad, India and SRTM DEM of 90 m resolution (Figure 2) from the Consortium for Spatial Information of Consultative Group on International Agricultural Research (CGIAR-CSI), USA. Figure 3: Geo referencing of photographic map For manual delineation of watersheds, the hard copies of topographic maps were first of all scanned and geo-referenced using Erdas Imagine 8.6 (Figure 3). The watershed boundaries of study area were delineated on the topographic maps by drawing water divides of drainages with the help of contour lines. The confluence of drainages of study area with Beas river near Sansarpur Terrace was selected as the outflow point. The CARTOSAT and SRTM digital elevation models of the study area in.tiff format were used for the automated generation of watershed boundaries using MapWindow (4.8.3). The MapWindow (4.8.3) generated watershed following several steps like 'Pit fill elevation', 'slope grid', 'flow direction', and 'catchment area'. The 'Pit fill elevation' function fills the sinks in the DEM, the 'slope grid' function generates the slope of the area, the 'flow direction' function creates direction of flow for each cell based on the elevation of neighbouring cells and the 'catchment area function' finally generates watershed boundaries. 3. Results and Discussion The manual digitization resulted in 10 watersheds in the study area varying in size between 427.29 to 796.34 km 2 (Table 1). The CARTOSAT and SRTM digital elevation models produced the similar watershed boundaries, which indicated there was no significant effect of resolution of DEMs used in this study on the watershed generation. It resulted in 20 watersheds (Figure 4A) in the study area ranging from 70.19 km 2 to 761.60 km 2 in size. It has been observed that the terms basin, watershed and catchment are often used interchangeably 18
Manual and automated delineation of watershed boundaries a case study of Kangra region of western Manual and automated delineation of watershed boundaries a case study from Kangra region of western Amit Kumar, Himalaya, Ravinder India Dhiman in the literature (World Bank, 2001). Besides, the size of watershed may vary depending upon size of a stream. In order to avoid these situations, in India, a hierarchical system of hydrologic units has been proposed which include regions, basins, catchments, subcatchments and watersheds (AIS&LUP, 1990). Therefore, by following this system, the watersheds comparatively lesser in size were merged together or with the adjacent watershed (Figure 4B). The merging of these smaller watersheds finally resulted in the 10 watersheds in the study area ranging from 427 to 761.97 km 2 (Table 1). Figure 4: Automated water sheds from DEM (A) before and (b) After merging of smaller water sheds Table 1: Geographical area of watersheds Watershed ID Automated Watersheds Area (km 2 ) Manual Watersheds Area (km 2 ) 1 427.00 427.29 2 533.49 533.15 19
3 803.87 796.34 4 595.53 601.96 5 482.60 482.31 6 552.10 604.03 7 761.97 758.31 8 401.60 388.76 9 626.66 614.53 10 554.23 532.32 It was observed that the manual and automated approach initially resulted in dissimilar watersheds. Later, when the size of automated watersheds was adjusted to 500 km 2, both approaches produced same number of watersheds with more or less similar spatial patterns (Figure 5). Figure 5: Automated and manually derived auto shed 20
The manual approach was observed as tedious, time consuming and had limitations as it required inputs in the form of topographic maps, which is a sometimes difficult to procure. The precise delineation of watersheds also requires understanding of water divide on maps and geo-informatics related skills. In contrast, the inputs required for automatic delineation of watersheds are freely available and doesn t require much skilled knowledge. Besides, the user also gets a faster result. The watershed boundary line generated using automated approach is smoother compared to manually delineated watersheds. 4. Conclusions It was concluded that with the availability of open source software and spatial database in conjunction with geo-informatics have made the process of watershed delineation now simpler. This process was otherwise troublesome and time consuming. The watershed boundaries produced through automated approach is accurate, smooth and requires lesser effort and time as compared to manual methods. The difference in resolution of DEM used in this study didn t affect the result but to what extent this increase or decrease in resolution doesn t show the difference may be a separate study. Overall, it was identified that the automated watershed delineation may be a useful in case of hilly mountainous terrain, which consists of rugged undulations with numerous small tributaries. Acknowledgement The authors are thankful to Dr. P. S. Ahuja, director, CSIR-IHBT, Palampur for facilities and infrastructure. We acknowledge CGIAR-CSI, USA and NRSC, Hyderabad for the DEM, and developers of Map Source software used in this study. The Council of Scientific & Industrial research is acknowledged for financial support. This is CSIR-IHBT communication no 3412. 5. References 1. AIS&LUP, (1990), Watershed Atlas of India, All India Soil and Land use Survey, Department of Agriculture and Cooperation, Government of India. 2. http://srtm.csi.cgiar.org/ (viewed on 9 May 2013). 3. http://earthsci.org/education/fieldsk/topmap.htm (viewed on 9 May 2013). 4. http://mapwindow4.codeplex.com (viewed on 9 May 2013) 5. http://www.esri.com (viewed on 9 May 2013) 6. IMSD, (1995), Integrated Mission for Sustainable Development technical guidelines, National Remote Sensing Agency, Department of Space, Hyderabad, India. 21
7. Kakade, B.K., and Hegde, N.G., (1998), Sustainability Indicators in Watershed Management. In: Proceeding of the national workshop on watershed approach for managing degraded land in India - challenges for the 21st century, 1998, New Delhi, pp 295-302. 8. Paranjape, S., Joy, K.J., Machadeo, T., Varma, A.K., and Swaminathan, S., (1998), Watershed based develeopment a source book, Bharat Gyan Vigyan Samithi, New Delhi, India. 9. Savant, G., Wang, L., and Truax, D., (2002), Remote sensing and geospatial applications for watershed delineation, ISPRS Archives, 34(1). 10. Singh, P., Behera, H.C., and Singh, A., (2011), Impact and effectiveness of watershed development programmes in India (Review and Analysis Based on the Studies Conducted by Various Government Agencies and Other Organisations), Centre for rural studies, National Institute of Administrative Research, Mussoorie, Uttarakhand, India. 11. Soliman, M.M., Lamoreaux, P.E., Memon, B.A., Assaad, F.A., and Lamoreaux, J.W., (1998), Environmental Hydrogeology, CRC Press, USA. 12. USDA, (2003), Fact sheet from the United States Department of Agriculture Natural Resources Conservation Service, USA. 13. WBD, (2012), Federal Standards and Procedures for the National Watershed Boundary Dataset (WBD), Techniques and Methods (11 A3), Third edition, 2012, U.S. Department of the Interior U.S. Department of Agriculture, U.S. Geological Survey Natural Resources Conservation Service. 14. World Bank, (2001), Watershed Management Window, Technical Note. Bank- Netherlands Water. 22