Assessment of soil erosion risks in response to land-use and land-cover changes in Coka watershed, Southern Ethiopia

Figures & data

Figure 1. Location map of the study area.

Figure 2. Processing flowchart for modeling soil erosion in the catchment.

Table 1. Observation data set and source.

Data type	Format	Source
Rainfall data	Table (xls)	National Meteorological Agency (NMA), Ethiopia
Satellite image	Raster (tif)	United States Geological Survey (http://earthexplorer.usgs.gov/)
Soil properties	Vector image (shf) +Tables (xls)	Food and Agricultural Organization (FAO), Ministry of Agriculture, Federal Government of Ethiopia
Topographic data	Raster (tif)	Shuttle Radar Topographic Mission (SRTM), (http://earthexplorer.usgs.gov/)

Table 2. (K) factor values corresponding to the soil texture and organic matter content Randolph (2004).

Textural class	Organic Matter (%)
	≤2	2–4	≥4
Fine sand	0.16	0.14	0.10
Very fine sand	0.42	0.36	0.28
Loamy sand	0.12	0.10	0.08
Loamy very fine sand	0.44	0.38	0.30
Sandy loam	0.27	0.24	0.19
Very fine sandy loam	0.47	0.41	0.33
Silt loam	0.48	0.42	0.33
Clay loam	0.28	0.25	0.21
Silty clay loam	0.37	0.32	0.26
Silty clay	0.25	0.23	0.19

Table 3. Description of land-use and land-cover classes in the Coka watershed.

Land-use types	Description
Cultivated land	This land-use type includes areas currently under crop, fallow land under preparation and rural settlement housing.
Bare lands	Land use type no vegetation cover, or with rocky land.
Settlement	Urban area (MudullaTwon extension)
Bush/shrub land	Land covered by small trees, bushes/shrubs.
Grasslands	Land covered by grass and small shrubs dominated by grass
Forest lands	Area dominated by high and dense natural forests and dense plantation trees including eucalyptus.
Water body	Back flow water of Gilgel gibe 3 dam.

Figure 3. Thematic maps of R-factor (a), K-factor (b), LS-factor (c), C-factor (d), and P-factor (e) of the Coka watershed.

Table 4. Area distribution of RUSLE factors values in Coka watershed.

R Factor (Mj ha^−1 yr^−1)			Area
			(ha)	(%)
653.8 − 680.5			858	23
680.5 − 711.3			1679	45
711.3 − 760.1			1194	32
K factor	Rank
0.10 − 0.15	Low		410.4	11
0.15 − 025	Moderate		2537.1	68
0.25 − 0.37	High		783.5	21
Ls factor
0 − 2			1007.4	27
2 − 5			8-Dec	19
5 − 10			895.4	24
10 − 15			671.6	18
15 − 30			447.7	12
LULC types	C-factor	Soil loss (t ha^−1yr^−1)
Forest land	0.001	2.3	859	23
Bushland	0.01	23.3	685	18.3
Grassland	0.01	23.3	631	16.9
Urban area/settlement	0.05	21.9	23	0.6
Bare land	0.6	236.2	66	1.8
Cultivated	0.15	65.8	1435	38.5
Water body	0	0	32	0.9
LULC types	Slope (%)	P-factor
Agricultural land use	0 − 5	0.1	20	1.4
	5 − 10	0.12	58	4
	10 − 20	0.14	152	10.6
	20 − 30	0.19	609	42.4
	30 − 50	0.25	489	34.1
	50 − 100	0.33	107	7.5
			1435	100
Non-agricultural land-use	All	1	2296

Table 5. Soil erodibility (K) factor values of different textures and organic matter content.

Sample site	LULC types	Northing	Easting	OM %	Soil Texture class	K-value
TC1	FL	340298	798994	2.21	Loamy Sand(LS)	0.10
TC2	GL	340160	798622	2.98	Sandy Loam(SL)	0.24
TC3	FL	34095	799779	3.20	Loamy Sand(LS)	0.1
TC4	BuL	340002	798665	3.20	Sandy Loam(SL)	0.24
TC5	BaL	341107	802536	2.48	Sandy Loam(SL)	0.24
TC6	CL	341062	802861	1.43	Sandy Loam(SL)	0.27
TC7	FL	340238	805701	3.07	Loamy Sand(LS)	0.1
TC8	FL	340963	802826	2.80	Sandy Loam(SL)	0.24
TC9	CL	341361	804929	1.52	Silty clay loam(SiCL)	0.37
TC10	GL	341301	806789	2.01	Silty clay(SiC)	0.25
TC11	CL	341224	806876	1.58	Silty clay loam(SiCL)	0.37
TC12	CL	341323	803765	1.91	Sandy loam(SL)	0.27
TC13	BuL	341312	801547	2.63	Silty clay loam(SiCL)	0.32
TC14	FL	340293	802985	3.63	Clay loam(CL)	0.25
TC15	BaL	340959	799240	1.76	SandyClay Loam(SCL)	0.28
TC16	GL	340954	799779	3.07	Sandy Clay Loam(SCL)	0.25
TC17	FL	337357	802524	4.67	Clay(C)	0.19
TC18	BUL	339897	802548	2.64	Clay(C)	0.23
TC19	GL	341122	802275	2.22	Clay(C)	0.23
TC20	FL	340859	801022	3.17	Clay(C)	0.23

T-Tembaro, C-Coka watershed, CL- cultivated land, FL-forest land, BUL- bush land, BaL-bareland, GL- Grassland.

Figure 4. Spatial distribution of soil loss within the study area.

Table 6. Estimation of soil erosion rates.

Soil loss (t ha^−1yr^−1)	Erosion risk	Priority area	Area
			(ha)	(%)
<5	Very low	V	299	8
5–10	Low	VI	224	6
10–18	Moderate	III	485	13
18–50	High	IV	410	11
50–100	Very high	II	746	20
> 100	Severe	I	1567	42

Randolph, J. (2004). Environmental land use planning and management. Island Press.

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