Demarcation of Priority Microwatersheds in 3B4B 1-6 And

Home , Lohit district

Demarcation of Priority Microwatersheds in 3B4B 1-6 and 3B4C1-6 Watersheds of 3B4B and 3B4C Subcatchments ( Lohit Catchment) of Brahmaputra Basin, Lohit and Lower Dibang Valley districts of Arunachal Pradesh and Tinsukia district of Assam

ABSTRACT

1. Survey Area : 3B4B& 3B4C Subcatchment (Lohit Catchment) of 3B4 Catchment in the Water Resource Region-3, Lohit & Lower Dibang Valley districts of Arunachal Pradesh and Tinsukia district of Assam 2. Location : 950 35’ 0” to 970 25’0” E Longitude and 27 035’ to 280 25’ N Latitude 3. Total Area : 928408 ha 4. Period of field visit : December, 2011 to January 2012 5. Type of Survey : Rapid Reconnaissance Survey using Remote Sensing Technique 6. Base Material : Survey of India Toposheets (1:50,000) and IRS-P6 LISS-III Precision Geo-coded FCC(3, 2, & 1) Satellite Imagery (1:50,000)

7. Extent of different Runoff Potential Mapping Units

Sl.No. RPMU Runoff Potential Value Area ( ha.) (%) 1 AL01 56 11389 1.23 2 AL02 54 24428 2.63 3 AL03 60 3046 0.33 4 AL04 53 300 0.03 5 AL05 57 10159 1.09 6 AL06 57 5043 0.54 7 AL07 66 8298 0.89 8 AL08 56 2430 0.26 9 AL09 58 1448 0.16 10 AL10 54 10396 1.12 11 AL11 54 14745 1.59 12 AL12 56 7915 0.85 13 AL13 61 4404 0.47 14 AL14 56 8500 0.92 15 AL15 60 5130 0.55 16 AL16 55 2345 0.25 17 AC01 57 1748 0.19 18 AC02 61 1691 0.18 19 AC03 54 954 0.10 20 AC04 62 422 0.05 21 AC05 70 65 0.01 22 AC06 59 1731 0.19 23 AC07 57 350 0.04 24 CG01 65 60 0.01 25 CG02 65 97 0.01 26 CG03 74 140 0.02 27 CG04 63 1240 0.13 28 CG05 73 455 0.05 29 CG06 62 302166 32.55 30 CG07 64 121211 13.06 31 CG08 86 59293 6.39 32 CG09 85 11316 1.22 33 CG10 85 9568 1.03 34 CG11 88 17147 1.85 35 CG12 84 9797 1.06 36 CG13 83 2853 0.31 37 CG14 92 76034 8.19 38 CG15 59 17459 1.88 39 CG16 73 3745 0.40 40 CG17 78 101 0.01 41 CG18 73 1918 0.20 42 CG19 70 384 0.04 43 CG20 80 299 0.03 44 CG21 67 458 0.05 45 CG22 57 660 0.07 46 CG23 67 844 0.09 47 CG24 68 404 0.04 48 CG25 60 1716 0.18 49 SNOW 0 121591 13.10 50 RIVR 0 35344 3.81 51 LS 0 3264 0.35 52 HS 0 585 0.06 53 WB 0 1322 0.14 Grand Total 928408 100

8. Hydrological Divisions :Water Resource Region (3) Basin (3B) Catchment (3B4) Subcatchment (3B4B) Watersheds (3B4B 1, 2, …..) Subwatersheds (3B4B 1a,.b, .c...... ,) Microwatersheds (3B4B1a1..., 3B4B2a1, ...)

9. Soil Erosion Status of the survey area:

Lower Erosion Classes Lohit Dibang Tinsukia Area (ha) % Valley None to slight 11040 19605 22315 64310 6.93 erosion Slight to Moderate 294289 18683 649 313621 33.78 erosion Moderate erosion 156636 7155 8724 172515 18.58 Moderate to 111813 3790 3857 119460 12.88 Severe erosion Severe erosion 947923 1078 6149 102019 10.99 Misc. 149863 4764 7479 162106 17.46 Total 818149 54857 55402 928408 100

(ii)

10. Priority Categorization :

Sl. Priority Category No. of Area (ha.) Percentage No. Microwatersheds

1 Very High (above 70) 483 341356 36.76 2 High (66-70) 213 145201 15.64 3 Medium (61-65) 467 293079 31.57 4 Low (56-60) 122 91890 9.90 5 Very Low (55 & below) 80 56882 6.13 Grand Total 1365 928408 100

11. State and District wise Priority Categorization:

Priority Arunachal Pradesh Assam Area (ha) % Category Lohit Lower Dibang Valley Tinsukia Very High 339151 2205 341356 36.76 High 142114 3087 145201 15.64 Medium 268984 14559 9536 293079 31.57 Low 56154 14741 20995 91890 9.90 Very Low 11746 20265 24871 56882 6.13 Total 818149 54857 55402 928408 100.00

12. Salient Features:

◙ 3B4B subcatchment has been subdivided into 1365 microwatersheds following the delineation and codification method outlined in Watershed Atlas of India (1:1 M scale). ◙ Out of 928408 hectares surveyed area, 341356 ha. (36.76%) covered by 483 microwatersheds have been categorized under very high priority area and 145201 ha. (15.64%) covered by 213 microwatersheds have been categorized under high priority area which need immediate attention for suitable runoff control measures under integrated watershed development programme. All the very high and high priority areas fall in Arunachal Pradesh only. ◙ In Lohit district of Arunachal Pradesh, 339151 ha (36.53%) & 142114ha (15.30%) and in Lower Dibang Valley district 2205 ha (0.23 %) & 8404ha (0.33%) are under very high & high priority category respectively. ◙ About 4703 ha (0.51%) area of the survey area is unmanaged while 182279 ha. (19.63%) area is moderately managed.

◙ Severely eroded lands occupy 102019 ha (10.99%) while moderately to severely eroded land covering 119460 ha (12.88%) need proper soil water conservation practices.

(iii) HOW TO USE SOIL SURVEY REPORT This report on Report on Demarcation of Priority Microwatersheds in 3B4B 1-6 and 3B4C1-6 Subcatchment ( Lohit Catchment) of Brahmaputra Basin, Lohit and Lower Dibang Valley districts of Arunachal Pradesh and Tinsukia district of Assam aims at identifying the microwatersheds which are relatively more prone to flooding and seasonal water logging and need the flood control measures. Further, it furnishes information on general characteristics of the catchments with particular reference to their location and extent, physiography, relief and drainage, geology, climate, land use and soils of the area also. The subcatchment is delineated and codified following the codification system of Watershed Atlas of India (WAI) published by Soil & Land Use Survey of India in September, 1990. The surveyed area comprises 12 watersheds 3B4B( 1-6),) and 3B4C(1-6) of WAI which are subdivided into 177subwatersheds and finally into 1365 microwatersheds. Subwatersheds are codified by suffixing small case English alphabets with the watershed code e.g. 3B4D1a, 3B4D1b etc and microwatersheds are codified by affixing Arabic numerical with the subwatershed code, e.g., 3B4B1a1, 3B4B1b1 etc. Within a microwatershed, Runoff Potential Mapping Units (RPMUs) are demarcated and symbolized with alphanumeric codes viz. AL01, AL02, AC01, AC02, CG01, CG02 etc. The Runoff Potential Mapping Units (RPMU) is established by visual interpretation of False Color Composites (FCC) of IRS-P6 LISS-III followed by field verification. The RPMUs represent the landscape, physiography, slope, soil characteristics, existing soil conservation status, land use and severity of erosion of each mapping unit. These Runoff Potential mapping units are described in the Table 6 on ‘Legend to Runoff Potential Mapping Units’. Each of these units is assigned its runoff potential (RP) value which indicates the potential runoff from the microwatershed. Differentiating morphological characteristics of the Run-off Potential Mapping Units have been depicted in the Table 7. Based on Run-off Potential (RP) value and the extent of RPMU in a microwatrshed, the Runoff Potential Index (RPI) values of all microwatersheds are computed which is given in the ANNEXURE-I. The relative priorities are assigned based upon the Runoff Potential Index (RPI) of the microwatersheds. Higher the value of Runoff Potential Index (RPI) indicates higher priority where as the lower value indicates lower priority. The list of microwatersheds under different priority categories are given in ANNEXURE-II. Microwatersheds categorized under very high and high priority are to be selected for management of flood prone area under FPR Scheme. Both treatable and non-treatable lands are occupied by each priority (very high or high category) micowatershed. The ratio of treatable and non-treatable lands in a priority microwatershed varies with the kind, degree and extent of the degraded lands occupied by the same microwatershed. Each map sheets on 1:50,000 scale depicting the drainage network, hydrological units, runoff potential mapping units and administrative boundaries are appended with this report. For any further clarification, information or comments contact may be made to: Chief Soil Survey Officer Soil Survey Officer Soil and Land Use Survey of India Soil and Land Use Survey of India I.A.R.I. Buildings, New Delhi 110012 E-Block, B. P. Township, Or Telefax-011-25843811 Kolkata-700094

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