Determination of potential sites for soil and water conservation in a block of Sitamarhi: A GIS-based approach

Sitamarhi is a flood affected district but as a block Nanpur is not a flood hit area. Only three or four panchayats of this block get affected at the time of Bagmati and Adhwara group floods. Bagmati and Adhwara group of rivers originate from the hills in Nepal and enter Indian Territory in Bihar in Sitamarhi district.

People living in this area with unforeseeable period of drought and flood. The growing demand of water could lead to the drying of the ponds and stream just after the monsoon season gets over. Soil and water conservation are activities that maintain the productive capacity of land in areas affected by or prone to soil erosion. Sometimes water flows across the block runs downhill from the Nepal hills carry sediment ranging fine clay to coarse sand. The sediment gets carried downstream with very gentle slope 1% to 3% towards the Bagmati River through the set of streams available in the block. Thus the Nanpur block is the host of huge amount of fine texture soil and water though the drainage. Very gentle slope allows the suspended particles in the stream water settle down and the siltation further make the stream silt up and proceeding upstream. Then garbage dumping and encroachment starts and now delineation of some streams in the block is a task.

The block is pond rich, public and private ponds exist in all the panchayats of the block. There are waterlogged chaur lands in two panchayats submerged nine months in a year. There is provision of outlets in the pataili chaur but low land of the chaur submerged nine month in year.

The area of Nanpur block is 111 sq. km. It extends between 26.484586 to 26.356856 latitude and 85.594629 to 85.745341 longitudes. The block is located in the Pupri subdivision 25 kms from headquarter Sitamarhi. The area is affected by flood and drought both. The annual average rainfall over the area is about 1200 mm.

Aim and Objectives: 

The aim is to find out suitable sites for establishing soil and water conservation structures in the block through MNREGS.
To study physical parameters of watershed and structures
To perform site suitability analysis using GIS.
To locate suitable sites for different structures to conserve soil and water.
Methodology: The stream network are found by survey, the satellite data are downloaded from Bhuvan
The soil texture is clay. Soil slope, texture, geomorphology and lineament features are extracted from Bhuvan services.
The Satellite data are downloaded from Bhuvan and arcGIS. All Public and private pond are surveyed physically and measured using Google earth. All drainage and stream structure verified physically and measured using Google earth. The depth and elevation measured by ArcGIS.
To increase the amount of available water by capturing rain water in one area for local use or for transfer to another area some conventional and non conventional structures are identified with suitable sites such as:

Renovation of existing ponds: The study reveals 245.88 acres of water bodies including 49 acres of chaur land. 107 ponds of this block have been identified for revival and renovation. Cutting and removal of dried silt manually and heap at in banks and other suitable places for optimum uses will bring 505053 cubic meter of additional storage capacity.

Sediments retention pond: Retention pond can provide both storm water strength reduction and water quality treatment by providing additional storage capacity to retain runoff and release it after stabilization at a control rate. We have 20 such structures are available near the ponds, which can be used. One of the panchayats of this block has a workable water retention pond; it settles runoff as well as grey water of a ward of the panchayat. Now as per GIS mapping and physical survey we have 52 locations to develop a retention pond. Retention ponds provide us improved storm water management, flood control and additional ground water recharge.

Steam based water conservation: As per GIS measurement thirty eight kilometres of stream bed of different width is available in the block. At the time of monsoon most of these structures flows downstream. The structures of this model can increase water retention significantly post monsoon. A stream based water storage model in which streams are dug along the bed through its natural course leaving natural bunds in between them. It is a low cost structure built in bed level of stream to harvest rain water and run off below ground level. It is aimed to recharge ground water tables of that area without construction of any pucca structure. The declining trends of ground water level in both long and short term is noticed. This model can accumulate the rainwater in sizeable quantity and make a positive impact on deteriorating quantity and quality of shallow aquifers. Thirty eight kilometres of the stream bed have been divided into 16 paths through GIS. 385 points have been identified in the streambeds to be dug. Through these structures we will able to conserve additional 26075 cubic meter of additional water and soil.

Chaur development: Pataili in Janipur panchayat is the main chaur in this block. The waterlogged area is divided as upland, medium land and low land according to elevation obtained by ArcGis. The chaur is spread over 49 acres of land, out of which 29 acres of land is low land. The 29 acres can be utilized to integrated aquaculture and rest 20 acres can be drained soon after the monsoon using the existing drainage system of the chaur after some renovation of channels.

Farm Pond: The Farm ponds are used for recharging ground water and protective irrigation. Most part of the block is highly suitable for construction of farm ponds. Beneficiaries are being selected at village level.

The block is both drought and flood prone and mainly depends on agriculture. It has become essential to conserve soil and water resource in proper manner. Hence site suitability analysis is being carried out based on runoff, drainage density, slope, soil and lineament features. The identification of suitable sites for these structures is an important step towards maximizing quality water availability and land productivity in Nanpur block and a support system to panchayats in planning the work of water conservation especially through MGNREGA. The main objective was to identify suitable sites and the number of structures required to harvest rainwater and soil.