Coastal watersheds differ from inland by their unique features including proximity to the ocean, weather and rainfall patterns, drainage system, subsurface aquifer conditions and geomorphological units. Land use changes and competing needs for water resources are especially more distinctive to such watersheds. This difference leads to put forward the Integrated Coastal Zone Management (ICZM), and is deemed to provide an operational tool for future researchers, developers and policy makers. Some important attributes necessary for watershed management in terms of land capability zonation include drainage, altitude, geology and slopes. The paper incorporates results of representative watershed namely Shringar Tali watershed. GIS technique was used to generate layers like drainage and springs, geology, contour, slopes and Digital Elevation Model (DEM), essential for watershed management. On the basis of interpretation of layers and superimposed picture obtained, Land Capability Zonation Map (LCZM) was prepared. The scope for spring sanctuary development, agro-forestry and aquaculture development is discussed in the paper.
The watershed management programs essentially envisage three main objectives namely to prevent erosion, to enhance water availability and to generate biomass [
Coastal watershed management is unique and hydrogeologically complex because the rhythm of tides keeps surface- and subsurface hydrogeological conditions changing throughout the day [
A review of literature reveals that there has been a growing trend of using GIS technique for the watershed management, since it helps in rapid analysis and categorization of land [
This paper, which is a case study from Konkan Coast region in the state of Maharashtra, demonstrates how the GIS technique was utilized in management of the Shringar Tali watershed.
The Konkan coastline having approximately 720 km length is dissected by a number of estuaries and creeks. It includes some significant physiographic features that have a bearing on climate. Based on Landsat imagery, a number of linear features were identified over the Konkan coast [
The Konkan region has a typical westward drainage originating from Western Ghats popularly known as Sahyadris. There are number of NNW-SSE flowing tributary streams, 10 km to 20 km in length, which empty their water into the westerly flowing rivers. Shringar Tali stream, representative of these streams originates on lateritic plateau and meets E-W flowing Vashishti estuary is the fifth order stream. It is included in the Survey of India toposheet nos. G 47/3 and G 47/6. The area is bounded by latitudes between 17˚28'N and 17˚34'N and longitudes between 73˚12'E and 73˚17'E. Its basin area is 43.32 sq km and maximum elevation from sea level is 240 m. It is 10.5 km in length (
Some important attributes necessary for watershed management in terms of Land Capability Zonation include drainage, altitude, geology and slopes. The Survey of India (SOI) toposheets pertaining to the Shringar Tali
watershed were scanned and digitized for generating the layers of these spatial parameters. The digitized data was utilized for 1) preparing primary layers to cover drainage and spring, contour, geology and 2) deriving secondary layers to generate Digital Elevation Model (
Layer I (Streams and Springs): First step in watershed analysis is to draw the drainage divide and mark all the streams present within it. Then follows the ordering of streams: the smallest fingertip streams being designated by order 1. When two first order streams join, a segment of order 2 is formed; and so forth. The data so obtained is utilized to compute the ratio of number of segments of a given order (Nu) to the number of segments of the next higher order (Nu + 1) called bifurcation ratio using following form
It can be seen from
A separate layer of springs was prepared. It was superimposed over a layer of drainage to ascertain relationship between these attributes. The superimposed picture indicates that majority of springs emerge along the streams (
Layer II (Area-Altitude): The area altitude analysis was carried out to obtain the relationship of horizontal
Stream order | No. of streams | Bifurcation ratio |
---|---|---|
1 2 3 4 5 | 159 33 7 3 1 | 4.81 4.71 2.33 3.00 |
cross-sectional watershed area to elevation. The layer II representing distribution of contours is shown in
Contour interval | No. of pixels | Pixel area | Area (sq m) | Area (sq km) | Area % | Relative area | Relative height |
---|---|---|---|---|---|---|---|
20 | 11,196 | 400 | 4,478,400 | 4.47 | 10.3588 | 0.100 | 0.083 |
21 - 40 | 2318 | 400 | 927,200 | 0.92 | 2.14466 | 0.049 | 0.166 |
41 - 60 | 2904 | 400 | 1,161,600 | 1.16 | 2.68684 | 0.062 | 0.250 |
61 - 80 | 10,583 | 400 | 4,233,200 | 4.23 | 9.79164 | 0.236 | 0.330 |
81 - 100 | 18,565 | 400 | 7,426,000 | 7.42 | 17.1767 | 0.396 | 0.416 |
101 - 120 | 17,021 | 400 | 6,808,400 | 6.80 | 15.7482 | 0.363 | 0.500 |
121 - 140 | 21,074 | 400 | 8,429,600 | 8.42 | 19.4981 | 0.450 | 0.583 |
141 - 160 | 17,134 | 400 | 6,853,600 | 6.85 | 15.8527 | 0.366 | 0.660 |
161 - 180 | 5270 | 400 | 2,108,000 | 2.10 | 4.87592 | 0.112 | 0.750 |
181 - 200 | 1505 | 400 | 602,000 | 0.60 | 1.39246 | 0.032 | 0.833 |
201 - 220 | 417 | 400 | 166,800 | 0.16 | 0.38581 | 0.009 | 0.916 |
221 - 240 | 95 | 400 | 38,000 | 0.03 | 0.08789 | 0.002 | 1.000 |
The hypsometric integral value obtained in the present case is 0.36. The hypsometric integral values throw light on the stage of development of the Watershed. The values over 0.50, 0.125 - 0.50 and below 0.125 are indicative of the youthful-, mature- and monadnock stage of development respectively. The value of 0.36 obtained in the present case thus suggests that the Shringar Tali watershed has reached a mature stage of development.
It is evident from
Layer III (Geology): Three formations viz. the laterite, basalt and sand/mud cover 29.15 sq km, 13.37 sq km and 0.80 sq km area respectively (
Layer IV (Slopes): Slopes are of utmost importance for rationalization of land-use in watershed because it gives the basis for land capability zonation which in turn assists in land use planning and soil conservation practices. The slopes were grouped into four categories that would suite the land capability criteria [
Contour interval | No. Of pixel | Pixel area | Area (sq m) | Area (sq km) | % area |
---|---|---|---|---|---|
0 - 20 | 11,196 | 400 | 4,478,400 | 4.4784 | 10.3588 |
20 - 80 | 15,805 | 400 | 6,322,000 | 6.3220 | 14.62314 |
81 - 100 | 18,565 | 400 | 7,426,000 | 7.4200 | 17.1767 |
>100 | 62,516 | 400 | 25,006,400 | 25.0064 | 57.84127 |
slope zone. Only 0.39% area is occupied by more than 30˚ slope.
The study area is endowed with rich eco-systems and scenic landforms. The ecosystems, if properly developed and managed, would certainly help minimizing environmental deterioration, promoting tourism, earning foreign exchange, generating jobs thereby preventing migration of population to mega cities like Mumbai and Pune, and
Slope interval | No. Of pixel | Pixel area | Area (sq m) | Area (sq km) | % area |
---|---|---|---|---|---|
< 7˚ | 69,644 | 400 | 27,857,600 | 27.8576 | 64.5282 |
7˚ - 20˚ | 32,494 | 400 | 12,997,600 | 12.9976 | 30.1071 |
20˚ - 30˚ | 5319 | 400 | 2,148,800 | 2.1488 | 4.97739 |
>30˚ | 418 | 400 | 167,200 | 0.1672 | 0.38729 |
elevating standard of living of local population.
A lot has been said and discussed on anthropogenic changes resulting deterioration of eco-systems. The Guhagar area in general and Shringar Tali watershed in particular is not exception to it. Unfortunately the term eco- development, rather than providing meaningful alternatives for conservation, has remained as fashionable slogan in under developed- and developing countries. The issue of eco-development, therefore, needs to be tackled adopting new thinking, conceptualizing holistic and innovative approach that would provide not only the scientific and technological solutions, but also take into account socio-economic needs.
On the basis of interpretation of the layers and superimposed picture obtained, Land Capability Zonation Map (LCZM) was prepared (
1) Prevention of Soil Erosion and Development of Water Resources,
2) Development of agro-forestry, and
3) Development of Aqua-culture and suggestions for CRZ Act.
Zone | Watershed treatment/eco-development | ||
---|---|---|---|
Prevention of soil erosion/water harvesting | Agro-forestry | Aqua culture/crz | |
I | Contour bunding, stream bank treatment, check dams on graded segment of stream, tidal regulator, masonry check dams, water spreading over paddy fields. | Canopy of coconut and beetle nut plantation, paddy field development, protection of mangrove forest & forestation of mangroves on deforested land wherever possible. | Aqua-culture development above strand line through small tanks and ponds, putting tidal regulator along stream, ban on drilling except for aqua culture with due precaution. |
II | Stream bank treatment for 3rd and 4th order streams, check dams across graded stretches, plantation to prevent gully erosion on stream originating in the zone, terracing & contour bunding on spurs. | Paddy cultivation on terraced land, canopy of orchids of jack fruits, pineapple, amla, and medicinal plants, grass. | Optimum depth of bore wells only up to 20 m datum line. |
III | Plantation to prevent gully erosion, terracing on minor spurs, stream bunds, check dams along graded stretches of streams. | Canopy of medicinal- and spice plantation, orchids of mango, cashew, eugenia jambolana. Allow wild growth of karvanda/grass. | Optimum depth of bore wells only up to 20 m datum line. |
IV | Controlled blasting in the vicinity of springs, storage of water in depressions on plateau, check dams, quarrying. | Mango and cashewnut plantation/grass. Phreatophytic flora in the vicinity of springs. |
The issue of spring sanctuary development requires consideration of two aspects, [
The spring water is stored in the tanks but much of it overflows and contributes to stream flow. It is possible to arrest this stream flow at the confluence of the first order streams by constructing small masonry bunds and larger size structure across second order stream immediately below these bunds (
One of the eco-friendly solutions for preventing erosion and generate finance is to undertake plantation program. The naturally occurring vegetation in the study area can be broadly classified into 4 main groups: (A) Littoral or mangrove type, (B) Open scrub type, (C) Moist deciduous type, and (D) Semi evergreen type. Plant communities in the area are not sharply defined as they merge imperceptibly one into another. However, altitude-wise demarcation is seen for some of the species due to marked difference in particle size, composition and pH of soils as also variation in chemistry of waters. In nutshell, vegetation does not show well-marked lateral characteristic canopies but certainly be differentiable between saline- and fresh water environments.
The Konkan coastal plain in general and study area in particular are rich in medicinal-, spice-, fruit-, food- and fodder plants [
and almost every village has these groves. Pineapple is another popular fruit cultivated on plains. As for timber, varieties of wood are in demand. With proper management of deciduous or semi-evergreen forests, most of the species can be brought into the approved range for wood based industries. Though Teak does not occur wild, it can be successfully introduced and cultivated as seen from the old teak plantations. Some of the highly palatable fodder grasses are present in the area. The area is quite rich in medicinal plants. There is good scope for introduction and cultivation of several useful species required by pharmaceutical firms.
Ecological setting of land adjoining Vashishti river and graded lower stretch of Shringar Tali stream below 20 m altitude is quite conducive for aqua culture. But these activities pose a problem of environmental degradation by way of deforestation of mangrove forest, pollution and so on. Therefore a few norms can be laid down while undertaking aqua culture development activity. These norms should cover density of aqua-culture tanks, ideal geomorphic setting along the tidal inlet, and cheaper eco-friendly alternative with optimum size of the tank for encouraging local fisherman communities to undertake aquaculture activity.
It has been a practice to lift seawater from estuary, creek or tidal inlet during high tide for supply to aqua culture tanks. The water so lifted contains undesirable material such as clay particles, tiny alive fish and other un-de- composed organic material. The filtering of water through costly filtration mechanism is necessary to remove such undesirable material. One way to overcome this problem is to obtain saline water from bore wells. Tectonic setting of the area permits recharging of seawater into deeper aquifers through fractures and joints. Therefore, bore wells drilled below 20 m altitude are high yielding but release saline water. This situation prompted to suggest that rather than lifting seawater from surface it may be obtained through series of bore wells. A due precaution, however, is necessary to seal the shallow aquifer to prevent leakage of fresh water into deeper aquifer.
The recommended dimension of tanks 0.5 to 1.0 sq ha area [
The periodic discharge of wastewater from the aqua tanks is the source of pollution since it contains organic feed, excretory matter and dead fish. As has been mentioned earlier mud flats and mangrove forests serve as
breeding ground for fish, crustacean, lamellibranch, gastropod etc. Pollution through aqua-culture activity is a threat to their existence. Research to use organic waste generated through aqua-culture as manure demand consideration.
The beach and mud flat environments are endowed with variety of biogenic structures formed due to feeding, browsing and crawling habits of the crustacean, gastropod, lamellibranch etc. These structures are not only beautiful but also generate curiosity among the visitors, particularly young ones. The places behind mangrove forests provide ideal sites for aqua-ponds to habitat these organisms (
The Shringar Tali watershed, a representative of NNW-SSE running streams originating on lateritic plateau, has been selected to suggest a model for watershed development. The Shringar Tali is a 5th order stream having a basin area of about 43.0 sq km. This basin has reached a mature stage of development as evident from hypsometric data.
On the basis of interpretation of the layers and superimposed picture obtained, treatment oriented Land Capability Zonation Map was prepared (LCZM). On the basis of comparative study of these layers following strategy has been suggested:
1. Zone I: Land with < 7˚ slope is prescribed for coconut and, beetle nut canopy, and paddy cultivation; development of aqua culture tanks and ponds; and putting tidal regulator to prevent sea water ingress, and masonry bunds for storage of surface water and preventing downward movement of fresh groundwater. Inputs prescribed for CRZ Act need to be practiced in this zone.
2. Zone II: Land between 7˚ to 200˚ slope is considered to be treatable with soil conservation measures such as stream bank treatment along graded segments of the streams, check dams, plantation to prevent gully erosion, terracing and contour bunding; and suitable for food-, fruit-, medicinal-, spices- and fodder plantation.
3. Zone III: Land between 200 and 300, is categorized for prescribing soil conservation technique such as check dams and stream bund to prevent gully erosion, terracing on minor spurs etc.; and suitable for fruit-, medicinal-, and fodder plantation, and
4. Zone IV: Land having > 30˚ and < 7˚ slope on plateau is classified as suitable for soil conservation techniques such as check dams, diverting surface runoff into quarry pits or natural depressions, controlled blasting for development of springs and; orchids of fruit and fodder cultivation.
The extent of laterite plateau in Konkan coastal plain is 4298 sq km. A number of NNW-SSE trending streams have carved their path through this plateau. The Shringar Tali watershed is one of the representatives of these streams. The model suggested for this watershed for management and eco-development, if attempted as a pilot project, could be useful in similar such watersheds with necessary changes.
Author is thankful to Prof. S. S. Thigale for the valuable guidance, help during fieldwork and critically going through the manuscript and to the Head, Department of Geology, University of Pune for extending the facilities.