Prioritization index of soil erosion intensity for management practices within Mountainous River using Geomatics

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Prioritization index of soil erosion intensity for management practices within Mountainous River using Geomatics

Dr. Vikas Vatsa¹, Nilanjana Roy², Vijaypal Singh Rana³

M& E Consultant, ICFRE, Dehradun Uttarakhand,

Associate, Social & Environmental Management Society, Uttarakhand, Consultant, Watershed Management Directorate, Dehradun, Uttarakhand,

Abstract

Mountainous rivers are always prone to severe soil erosion. Streams runoff from steep slope carriying heavy sediment yield to the plain. In the present study an attempt has been made to prioritize the microwatershed (MWS) for management practices within a subwatershed (SWS) Priority index was made based upon the intensity of soil erosion zone in MWS. This study identified and statistically ranked the MWS in order to do further analyses for protection measures. The main elements of soil erosion intensity assessment in this study are land cover, slope and forest density.

Keywords: Sub Watershed, Microwatershed Soil erosion intensity, Priority index

INTRODUCTION

Hydrologically watershed is an area from which runoff flows to a stream / river from a single point.

For development, planning and implementation of conservation activities large watersheds are not suitable, so it could be done on specific area where degradation level of natural resources is severely high. These few selected areas according to the size are classified as a Subwatershed or Microwatershed and prioritize for management practices (Desai et al 2017). Soil erosion is a naturally occurring process over the land surface (Ritter 2015). The acceleration of soil erosion is generally a symptom of human activities while the agents of soil erosion are water and wind, each contributing a significant amount of soil loss each year. (Balasubramanian A. 2017).

Watershed management aims to solve the problems of soil and water not in terms of any one resource but on the basis that all the resources are interdependent and must therefore, be considered together (Pandey, 2005). Soil erosion is one of the most critical environmental hazards of recent times. A large area suffers from soil erosion, which in turn, reduces productivity. Methods such as the Universal Soil Loss Equation (USLE) or Revised Universal Soil Loss Equation (RUSLE) are widely used for the estimation of soil erosion from catchment areas.

Using Remote Sensing and GIS technique for soil erosion estimation is effective for prioritization and conservation measures in a catchment area (Biswas & Sujata 2012). There are various models and processes involved in GIS for soil loss assessment and soil conservation planning (Gupta & Uniyal 2012). Most of these models required data like geomorphology, soil profile, rainfall etc. In the present

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study an attempt has been made to prioritize the microwatersheds within a Subwatershed for management practices where detailed data is not available.

STUDY AREA

The mountainous river Song drains the central and eastern part of Dehradun valley. It rises as a spring-fed stream from the south facing slopes of the Mussorie ridge to the east of Rajpur.

Underground waters feed this river and its tributaries. It flows along a south-west course in its upper reaches. Thereafter it slowly turns towards east and joins the Ganga river between Rishikesh and Haridwar. This river is one of the largest rivers draining Dehradun valley. Steep slopes hem the northern catchment of this river. Its gradient is very steep in the upper course. However, the speed of this river is greatly reduced once it enters the valley. (Negi 1991).

The sub-watershed of river Song is in Ganga A Basin in Uttarakhand, India is considered for this study. The study area extends between North Latitudes 30° 27’30” to 30°01’0” and East Longitudes 77° 59’ to 78° 19’ with an aerial extent of 1050.32sq.km. It includes 29 Micro-watersheds mainly Baldi, Bindal, Rispana, JakhanRao, Jollygrant, Kansrau, Bhaniawala etc.

Major towns and area of Song sub-watershed include Dehradun, Miyanwala, Raipur, Upper Nakronda, Tunwala, Thano, Motharwala, Doiwala, Bhaniawala, Bulawala, Mazari Grant, Rani

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Pokhri, Laal tappad, Garhi Maychak and Satyanarayana. Part of the Rajaji National Park, namely the Lachhiwala range is also a part of the sub-watershed. (figure-1)

METHODOLOGY

Song Sub-watershed is one of the typical zones with regard to the erosion phenomenon development in the region. The factors which are taken in analysis for assessment of erosion intensity mapping are - land cover, forest density, and slope and drainage pattern (figure-2).

The data for the land cover was classified using hybrid classification of LISS-IV MX. Total 50 classes were classified using unsupervised classification. Merging of similar classes 6 major landuse classes were classified. Supervised classification was also carried out to identify landuse classes. Both the unsupervised and supervised classified images were used to finalise the pre ground survey map.

Ground knowledge was used to rectify and finalise the landuse map. Using ground information these classes were again merged into 6 major classes using supervised classification techniques. The major land cover classes were forest, agriculture, urban, water, barren and scrub (Table-1). Forest density map was prepared from Forest Cover map of Forest Survey of India (SFR-2015) data which was recoded for specific erosion classes to estimate the erosion pioneers (Table-2).

Figure 2 : Methodology Table 1: Category of land use.

CLASSES CLASSIFICATION SCHEME Erosion risk rating

Very dense Forest

All Lands with tree cover of canopy density of 70% and above

Low

Moderate dense forest

All lands with tree cover of canopy density between 40% and 70% above

Moderate

Open forest

All lands with tree cover of canopy density between 10% and 40%

High

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Scrub

All forest lands with poor tree growth mainly of small or stunted trees having canopy density less than 10 percent

Very high

Non Forest Any area not included in the above classes Very high

Table 2: Criteria for erosion risk base on land use and forest density.

Land classification Erosion risk rating

Natural vegetation with high density (forest), flat agriculture areas, natural and artificial aquatic areas and urban land

Low Natural vegetation with no high density (forests and shrubs), hilly agriculture areas and fruit yards

Moderate Natural vegetation with low density (areas with forest and shrub

degradation)

High

Areas without vegetation Very high

Figure4: Landuse and Forest Density Map of Study Area

The slope is another important element in the process of erosion risk assessment (O. Marko 2010).

Low erosion risk includes 0-10° of slope while moderate erosion risk includes 11°-15° of slope. 16°- 30° of slope is considered as high erosion risk and 31°-90° of slope is included under very high erosion risk category. The slope class distribution is given in (Table 3).

Table 3: Slope classification.

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Slope classification (grade) Erosion risk rating

0-10° Low

11-15° Moderate

16-30° High

31-90⁰ Very high

Figure 4: Digital Elevation Model and Slope Map of Study Area Preparation of Erosion Intensity Map & Priority Index

Soil erosion intensity assessment was done by giving weightage to all elements described above with consideration of drainage pattern. All the factor maps Forest Density, Landuse and slope were used to generate a composite map of soil erosion intensity. The Figure 4 shows the final product for Erosion intensity in Song Sub-watershed. where erosion class1(e1) had most intensity followed by e2 with moderate intensity, e3 with less intensity and e4 with least soil erosion intensity in catchment area.

Microwatershed wise area covered in each erosion classes were calculated through overlay operation in GIS (Table-4). Each intensity class was ranked by rank coordinate method (Rider 1952). Final rank of MWS is considered as Priority index.(Table-5)

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Fig. 5 : Distribution of areas according to erosion risk of Study area

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Table 4: Microwatershed wise erosion risk intensity area in Song Subwatershed

S.No. MWS Name Area% E1 Area% E2 Area% E3 Area% E4

1 Balawala 41.21 55.20 3.43 0.15

2 Baldi Nadi 57.63 28.15 11.58 2.64

3 Bandal Nadi 59.18 18.29 20.23 2.30

4 Beriwararao 89.24 10.64 0.12 0.01

5 Bhaniyawala 78.66 20.71 0.63 0.00

6 Bidhalana Nadi 31.75 45.72 20.23 2.31

7 Bulindawalarao 87.71 11.76 0.47 0.06

8 Bullawalarao 76.48 22.91 0.59 0.02

9 Chiphaldi Nadi 67.34 22.01 7.59 3.05

10 Chittaur Rao 69.47 20.89 8.65 1.00

11 Churpanirao 87.85 11.55 0.44 0.16

12 Dubra 78.64 15.85 4.77 0.73

13 Golapani Rao 39.28 57.69 2.90 0.14

14 Jakhan Rao 47.79 25.78 24.70 1.73

15 Jakhanrao+ 25.04 45.20 27.05 2.71

16 Jamansot 74.32 24.88 0.78 0.02

17 Joli Grant 36.08 60.29 3.58 0.05

18 Kaluwala 45.08 52.55 2.35 0.02

19 Kansrao I 89.31 10.26 0.39 0.03

20 Kansrao II 90.13 9.22 0.56 0.08

21 Kishanpur 71.22 25.97 2.52 0.28

22 Kurkawala 4.16 91.95 3.88 0.00

23 Pantwala Rao 78.51 21.08 0.38 0.03

24 Ramgarhrao 79.85 19.30 0.70 0.15

25 Rispna Rao 24.76 68.90 5.97 0.36

26 Satyanarayan 40.88 58.14 0.96 0.02

27 Sirwal Garh 73.57 19.48 5.48 1.46

28 Song Nadi 54.39 29.10 15.28 1.23

29 Sukhrao 52.40 46.17 1.36 0.07

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Table5: Microwatershed wise Priority Index in Song SubWatershed

SN MWS

Rank of E1

Rank of E2

Rank of E3

Rank of E4

Sum of Rank

Priority Index

1 Balawala 22 6 14 14 56 13

2 Baldi Nadi 17 12 6 3 38 1

3 Bandal Nadi 16 23 3 5 47 7

4 Beriwararao 3 27 29 27 86 29

5 Bhaniyawala 7 20 22 29 78 28

6 Bidhalana Nadi 26 9 4 4 43 6

7 Bulindawalarao 5 25 25 19 74 25

8 Bullawalarao 10 16 23 24 73 24

9 Chiphaldi Nadi 15 17 8 1 41 3

10 Chittaur Rao 14 19 7 9 49 8

11 Churpanirao 4 26 26 13 69 18

12 Dubra 8 24 11 10 53 11

13 Golapani Rao 24 5 15 16 60 14

14 Jakhan Rao 20 14 2 6 42 4

15 Jakhanrao+ 27 10 1 2 40 2

16 Jamansot 11 15 20 23 69 19

17 Joli Grant 25 3 13 20 61 15

18 Kaluwala 21 7 17 25 70 20

19 Kansrao I 2 28 27 21 78 27

20 Kansrao II 1 29 24 17 71 22

21 Kishanpur 13 13 16 12 54 12

22 Kurkawala 29 1 12 28 70 21

23 Pantwala Rao 9 18 28 22 77 26

24 Ramgarhrao 6 22 21 15 64 17

25 Rispna Rao 28 2 9 11 50 10

26 Satyanarayan 23 4 19 26 72 23

27 Sirwal Garh 12 21 10 7 50 9

28 Song Nadi 18 11 5 8 42 5

29 Sukhrao 19 8 18 18 63 16

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Table6: Priority List of Microwatersheds in Song SubWatershed for treatment Priority Index MWS Name Priority

Index MWS Name Priority Index MWS Name

1 Baldi Nadi 11 Dubra 21 Kurkawala

2 Jakhanrao+ 12 Kishanpur 22 Kansrao II

3 Chiphaldi Nadi 13 Balawala 23 Satyanarayan

4 Jakhan Rao 14 Golapani Rao 24 Bullawalarao

5 Song Nadi 15 Joli Grant 25 Bulindawalarao

6 Bidhalana Nadi 16 Sukhrao 26 Pantwala Rao

7 Bandal Nadi 17 Ramgarhrao 27 Kansrao I

8 Chittaur Rao 18 Churpanirao 28 Bhaniyawala

9 Sirwal Garh 19 Jamansot 29 Beriwararao

10 Rispna Rao 20 Kaluwala

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Conclusion

Land cover is a very important element for assessment of erosion risk along with slope and drainage order. The methodology used for the study is capable of generalizing erosion intensity zone quite well over the entire Song Sub-Watershed. It accurately identifying areas of very high, high, moderate and low risk areas of erosion. Moreover, it also prioritized 29 MWS of the Song Sub Watershed for management practices. Baldi Nadi Microwatershed is more prone to erosion and should be prioritised, while BeriwaraRao microwatershed is more stable in terms of soil erosion. The study shows that due to lack of ancillary and ground data in mountainous watershed this method could provide opportunities of management practices and development work.

References

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