|
|
|
Selection of least cost paths for extraction of Forest Produce using Remote Sensing and GIS - A case study of Andhra Pradesh Forest Dept. India
Methodology
Sufficiently large area has been selected for the study en compassing the forests to search for potential alternatives. The analysis is carried out using Remote Sensing and GIS. Landuse/landcover map for the study area has been prepared using IRS-1D LISS-III data of December, 2000 with necessary groundtruthing.. The reconnaissance survey has been completed at this stage. The bamboo coupes are very near to the southern border i.e. river Krishna. It has been observed that the back waters in the reservoir due to the Srisailam dam are available for most part of the year and can be used for transportation. At Somashila village where a famous temple is present, the river is used by the pilgrims and so the banks are developed for bathing ghats. It is proposed as a depot. Also at Chintapally village there was old depot which is proposed as a depot..The Bamboo coupes are identified and a separate layer prepared. The existing depot at Kollapur is taken as only depot for another analysis. As it is necessary to consider existing roads and their condition, and roads cannot be delineated using RS data in forests due to closed canopy, a road layer has been prepared from SOI toposheet. The contour layer has been prepared using SOI toposheets and a Digital Elevation Model (DEM) is generated. The ordered drains have been delineated using Arc/Info software. The bridges, culverts are identified in SOI toposheet and these are adjusted so as to match the streams on superimposition. The road and stream intersections are also treated as bridges. In all the layers, the cell size is kept 50 m. The proposed road width is taken as 10 m. However as the final cost proportionately varies we can convert to any required width by changing the width proportionately through out length. It means that to traverse a cell vertically/horizontally we need to lay a road of 10x50 sq.m. If the cell is to be traversed diagonally the cost is multiplied by 1.414. In agricultural lands to make provision for the side drains etc. either side 5m extra procurement is proposed (i.e. 20x50 sq.m). From field investigations per hectare costs are obtained (to close approximations) from which the costs to traverse each cell as specified above have been arrived at. These are later divided by cell size to get costs for unit distance (i.e. one meter). For example to clear one hectare dense forest if it costs Rs. 40,000/-and for a cell it costs Rs. 2,000/-and for one meter it cots Rs.40/-. To avoid unnecessary crossing of streams, the costs of constructing culverts/bridges have been estimated stream order wise and assigned to streams. The existing roads have been classified into 4 classes namely metalled, unmetalled, cart track and foot paths. The metalled roads are assigned a cost of 1(lowest), unmetalled roads which require Rs. 50/- for a stretch of 50 m. for minor repairs. The cart tracks are generally 2.5 m wide, it is observed that it reduces expenditure by25% to what it costs otherwise to widen it to 10 m. Therefore it is seen that the cart track takes values (¾) th times the land use present beneath it in RS generated map. The foot paths are not considered at this stage. The water transportation system provides low speed but extremely high capacities. The capital costs of vessels is high but operating costs per ton-mile are extremely low. Environmental impacts are relatively low. Therefore it is given a value of “1”(the lowest). To control frequent switchovers from land to water which involves arrangements for loading/unloading, a barrier is created in edge cells of river throughout its length using AOI tools insuch a way that to cross it the path should atleast horizontally traverse one cell.It is assigned a high value of 5,00,000, (approximate cost of a small crane or development of a small port) except at Somashila village.The broad land use classes obtained from the RS data are further modified using various knowledge components. The roads, streams, bridges/culverts are induced into landuse. To avoid habitations, Waterbodies, rockoutcrops (obligatory points), these have been assigned a very high cost of 1,00,000 per cell. The approximate costs assigned after field investigations to clear/procure are shown in table1.A grid is obtained with these costs (say Weighted LU).Slope map in percentage is generated. As per the guidelines of the IRC; slope weight images for ruling gradient, limiting gradient, and exceptional gradients have been prepared as follows. If the slope of a cell falls in plain or rolling terrain a ruling gradient of 3.3% is advised.
Table1. Cost values assigned to different Land landuse units
| Land use |
Cost to traverse cell in Rs. |
Cost per unit dist. in Rs. |
| Dense forest |
2000 |
40 |
| Open forest |
1000 |
20 |
| Scrub |
500 |
10 |
| Sparse Scrub |
300 |
6 |
| Agriculture(20x50)m2 |
6000 |
120 |
| Habitations |
100000 |
2000 |
| Water bodies |
100000 |
2000 |
| Rock outcrops |
100000 |
2000 |
| Drains(1st order) |
5000 |
100 |
| Drains(2 nd order) |
20000 |
400 |
| Drains(3 rd order) |
30000 |
600 |
| Drains(4,5,6th order) |
100000 |
2000 |
| Bridges/Culverts |
1 |
0 |
| Roads(metalled) |
1 |
0 |
| Roads(unmetalled) |
50 |
1 |
| Roads(cart track) |
3/4th of the cost of landuse |
(Cost of LU)*3/200 |
| River,Hypothetical Barrier |
1, 5,00,000 |
0; 10,000 respectively |
|
|
|