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Soil Erosion Susceptibility Mapping of Imo River Basin Using Modified Geomorphometric Prioritisation Method

Peter C. Nwilo
Peter C. Nwilo
, 
Caleb O. Ogbeta
Caleb O. Ogbeta
, 
Olagoke E. Daramola
Olagoke E. Daramola
, 
Chukwuma J. Okolie
Chukwuma J. Okolie
 und 
Michael J. Orji
Michael J. Orji
   | 30. Sept. 2021
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Online veröffentlicht: 30. Sept. 2021
Seitenbereich: 143 - 162
Eingereicht: 24. März 2021
DOI: https://doi.org/10.2478/quageo-2021-0029
Schlüsselwörter
© 2021 Peter C. Nwilo et al., published by Sciendo
This work is licensed under the Creative Commons Attribution 4.0 International License.

Fig. 1

Map showing the location of the study area.
Map showing the location of the study area.

Fig. 2

Methodology workflow.
Methodology workflow.

Fig. 3

Sub-watershed map of Imo River Basin.
Sub-watershed map of Imo River Basin.

Fig. 4

Drainage map of Imo River Basin showing the stream order.
Drainage map of Imo River Basin showing the stream order.

Fig. 5

Erosion susceptibility map of the study area based on Cpc value. Cpc, compound parameter constant.
Erosion susceptibility map of the study area based on Cpc value. Cpc, compound parameter constant.

Fig. 6

Overlay of validation points on the erosion susceptibility map.
Overlay of validation points on the erosion susceptibility map.

Fig. 7

The ROC technique validation result. ROC, receiver operating characteristics.
The ROC technique validation result. ROC, receiver operating characteristics.

Coordinates of the ROC curve.

S/N 1 2 3 4 5 6 7 8 9 10 11 12
Sensitivity 1.000 1.000 1.000 1.000 0.833 0.667 0.500 0.333 0.333 0.333 0.167 0.000
1 – Specificity 1.000 0.714 0.429 0.286 0.286 0.286 0.286 0.286 0.143 0.000 0.000 0.000

Descriptive information of the validation points.

Point no. Location name Erosion type Easting Northing Average depth Area Source(s)
[mE] [mN] [m] [km2]
1 Ideato North Gully erosion 297084 650725 15–35 30.11–109.72 (Amangabara et al. 2015, Amangabara et al. 2018)
2 Ideato South 296988 643359 15–35 30.11–109.72
3 Okigwe 317303 643221 – 0.68
4 Obowo 319395 616106 05–20 8.39–30.12 Amangabara et al. (2015)
5 Ehime Mbano 309899 628529 – 0.55–2.090
6 Umuahia North Gully erosion 332166 617607 – 6.85–31.70 Channels Television (2018)
7 Aboh-Mbaise 309726 593501 – 0.76–1.530
8 Unuimo No active erosion 303363 636918 – – –
9 Ogwe 306703 551110 – – –
10 Obiaku 301950 540063 – – –
11 Nkpa 333293 623302 – – –
12 Ihitte-Uboma 316080 623687 – – –
13 Etche 293472 547770 – – –

Pearson correlation matrix of sub-watershed morphometric parameters.

Parameter Dd Fs Rbm Dt Re Rc Rf Cc H Rh Rn
Dd 1.00 0.16 (0.44) −0.14 (0.51) 0.28 (0.17) −0.14 (0.52) −0.05 (0.82) −0.14 (0.51) 0.05 (0.80) 0.22 (0.29) 0.13 (0.55) 0.38 (0.06)
Fs 0.16 (0.44) 1.00 −0.11 (0.61) 0.63** (0.00) 0.35 (0.08) 0.04 (0.87) 0.39 (0.06) −0.01 (0.98) −0.33 (0.11) −0.20 (0.34) −0.29 (0.15)
Rbm −0.14 (0.51) −0.11 (0.61) 1.00 −0.22 (0.28) −0.42* (0.04) −0.51** (0.01) −0.41* (0.04) 0.53** (0.01) −0.04 (0.84) −0.32 (0.12) −0.07 (0.76)
Dt 0.28 (0.17) 0.63** (0.00) −0.22 (0.28) 1.00 0.33 (0.11) 0.21 (0.31) 0.38 (0.06) −0.08 (0.71) −0.10 (0.63) −0.13 (0.53) −0.07 (0.75)
Re −0.14 (0.52) 0.35 (0.08) −0.42* (0.04) 0.33 (0.11) 1.00 0.67** (0.00) 0.99** (0.00) −0.70** (0.00) −0.35 (0.09) 0.11 (0.59) −0.35 (0.09)
Rc −0.05 (0.82) 0.04 (0.87) −0.51** (0.01) 0.21 (0.31) 0.67** (0.00) 1.00 0.66** (0.00) −0.96** (0.00) 0.06 (0.79) 0.52** (0.01) 0.05 (0.83)
Rf −0.14 (0.51) 0.39 (0.06) −0.41* (0.04) 0.38 (0.06) 0.99** (0.00) 0.66** (0.00) 1.00 −0.68** (0.00) −0.33 (0.11) 0.10 (0.63) −0.34 (0.10)
Cc 0.05 (0.80) −0.01 (0.98) 0.53** (0.01) −0.08 (0.71) −0.70** (0.00) −0.96** (0.00) −0.68** (0.00) 1.00 −0.01 (0.98) −0.51* (0.01) 0.00 (0.99)
H 0.22 (0.29) −0.33 (0.11) −0.04 (0.84) −0.10 (0.63) −0.35 (0.09) 0.06 (0.79) −0.33 (0.11) −0.01 (0.98) 1.00 0.81** (0.00) 0.99** (0.00)
Rh 0.13 (0.55) −0.20 (0.34) −0.32 (0.12) −0.13 (0.53) 0.11 (0.59) 0.52** (0.01) 0.10 (0.63) −0.51* (0.01) 0.81** (0.00) 1.00 0.80** (0.00)
Rn 0.38 (0.06) −0.29 (0.15) −0.07 (0.76) −0.07 (0.75) −0.35 (0.09) 0.05 (0.83) −0.34 (0.10) 0.00 (0.99) 0.99** (0.00) 0.80** (0.00) 1.00
Sum of correlation 1.76 1.63 −0.71 2.22 1.50 1.69 1.63 −1.35 1.92 2.31 2.10
Grand total 14.71 14.71 14.71 14.71 14.71 14.71 14.71 14.71 14.71 14.71 14.71
Final weights 0.120 0.111 −0.048 0.151 0.102 0.115 0.111 −0.092 0.130 0.157 0.143

Watershed prioritisation and final ranking for erosion susceptibility.

Sub-watershed ID Compound parameter constant value WSA final ranking
SW1 19.78 24
SW2 21.77 25
SW3 15.06 17
SW4 13.25 12
SW5 6.25 1
SW6 15.84 19
SW7 15.89 20
SW8 14.48 15
SW9 16.40 21
SW10 17.56 23
SW11 14.45 14
SW12 16.91 22
SW13 14.90 16
SW14 9.74 7
SW15 8.13 5
SW16 10.50 10
SW17 13.04 11
SW18 13.39 13
SW19 10.10 8
SW20 15.53 18
SW21 7.51 2
SW22 10.24 9
SW23 8.52 6
SW24 7.98 4
SW25 7.80 3

Formulas adapted for the computation of morphometric parameters.

S/N Morphometric parameter Formula Unit Reference
1 Basin area (A) The area enclosed by the watershed (GIS software analysis) km Horton (1945)
2 Basin perimeter (P) The perimeter of the watershed (GIS software analysis) km Horton (1945)
3 Basin length (Lb) Distance from outlet to the farthest point on basin boundary (GIS software analysis) km Schumm (1956)
4 Stream order (U) Hierarchical order [−] Strahler (1964)
5 Number of streams (Nu) Total stream number of all orders (GIS software analysis) [−] Strahler (1964)
6 Total stream length (L) Total stream length of all orders km Horton (1945)
7 Bifurcation ratio (Rb) Rb = Nu / (Nu + 1)where Rb = Bifurcation ratio; Nu = Total no. of stream segments of order ‘u’; Nu + 1 = Number of segments of the next higher order. [−] Schumm (1956)
8 Mean bifurcation ratio (Rbm) Rbm = Average of bifurcation ratios of all orders [−] Strahler (1957)
9 Drainage density (Dd) D = Lu / Awhere D = Drainage density; Lu = Total stream length of all orders; A = Basin area (km2) km km−2 Horton (1945)
10 Stream frequency (Fs) Fs = Nu / Awhere Fs = Stream frequency; Nu = Total no. of streams of all orders; A = Basin area (km2) no km−2 Horton (1945)
11 Drainage texture (Dt) Dt = Nu / P where Dt = Drainage texture; Nu = Total no. of streams of all orders; P = Basin Perimeter (km) no km−1 Horton (1945)
12 Elongation ratio (Re) Re = 2 / Lb sqrt (A / Π)where Re = Elongation ratio; A = Basin area (km2); Π = ‘Pi’ value i.e. 3.14; Lb = Basin length [−] Schumm (1956)
13 Circulatory ratio (Rc) Rc = 4 × Π × A / P2where Rc = Circularity ratio; Π = ‘Pi’ value i.e. 3.14; A = Basin area (km2); P = Basin Perimeter (km) [−] Miller (1953)
14 Form factor (Rf) Rf = A / Lb2where Rf = Form factor; A = Basin area (km2); Lb2 = Square of basin length [−] Horton (1932)
15 Compactness coefficient (Cc) Cc = P / 2 sqrt (ΠA)where Cc = Compactness Coefficient; P = Basin perimeter (km); A = Basin area (km2) [−] Horton (1945)
16 Basin Relief (H) H = Maximum relief − Minimum relief m Horton (1945)
17 Relief ratio (Rh) Rh = H / Lbwhere Rh = Relief ratio; H = Basin relief; Lb = Basin length [−] Schumm (1956)
18 Ruggedness number (Rn) Rn = Dd × (H / 1000)where Rn = Ruggedness Number; Dd = Drainage density; H = Basin relief [−] Strahler (1968)

Basic parameters of sub-watersheds (SWs) in the Imo River Basin.

Sub-watershed ID Basin area Basin perimeter Basin length No. of streams Total stream length Elevation
Max Min
[km2] [km] [–] [km] [m]
SW1 51.97 75.23 11.27 37 51.43 41 12
SW2 39.24 50.30 8.33 26 40.75 37 14
SW3 103.93 104.85 16.51 84 113.91 52 18
SW4 158.62 117.01 22.45 128 180.71 70 17
SW5 656.12 351.57 69.97 548 757.62 193 20
SW6 35.53 48.99 11.95 29 35.00 186 67
SW7 137.12 112.25 15.56 102 139.73 206 60
SW8 56.51 58.75 10.11 49 60.28 203 67
SW9 67.16 57.89 10.46 63 77.83 175 81
SW10 50.87 51.22 10.44 36 48.03 212 75
SW11 89.84 79.12 12.13 70 90.71 240 73
SW12 83.18 64.30 11.21 79 86.64 219 82
SW13 53.53 52.09 12.76 26 55.09 286 75
SW14 60.49 56.84 10.96 51 66.94 290 76
SW15 58.19 69.55 13.51 48 62.12 330 82
SW16 63.83 62.58 14.73 39 69.49 334 83
SW17 116.86 76.83 13.38 99 133.21 262 89
SW18 83.69 107.19 14.88 67 85.68 239 86
SW19 59.31 55.17 13.47 37 66.98 360 99
SW20 68.98 52.21 10.58 51 71.15 323 118
SW21 55.77 72.08 14.31 40 76.02 322 99
SW22 78.38 102.44 24.19 48 80.23 386 86
SW23 47.47 80.10 18.18 37 50.74 345 104
SW24 124.73 106.08 18.73 85 135.74 417 109
SW25 93.37 68.50 13.43 75 110.06 416 149

Linear, shape and relief parameters of sub-watersheds (SWs) in the Imo River Basin and its preliminary ranking with respect to soil erodibility.

Sub-watershed Linear parameters Shape parameters Relief parameters
Dd Fs Rbm Dt Re Rc Rf Cc H Rh Rn
SW1 0.99 (23) 0.71 (18) 5.57 (2) 0.49 (23) 0.72 (14) 0.12 (5) 0.41 (14) 2.97 (21) 29 (24) 0.003 (22) 0.029 (24)
SW2 1.04 (16) 0.66 (21) 4.50 (7) 0.52 (21) 0.85 (19) 0.20 (14) 0.57 (19) 2.28 (12) 23 (25) 0.003 (21) 0.024 (25)
SW3 1.10 (9) 0.81 (9) 3.96 (17) 0.80 (13) 0.70 (13) 0.12 (6) 0.38 (13) 2.92 (20) 34 (23) 0.002 (25) 0.037 (23)
SW4 1.14 (6) 0.81 (10) 4.70 (6) 1.09 (5) 0.63 (7) 0.15 (10) 0.32 (7) 2.64 (16) 53 (22) 0.002 (24) 0.060 (22)
SW5 1.16 (4) 0.84 (6) 4.80 (4) 1.56 (1) 0.41 (2) 0.07 (1) 0.13 (2) 3.90 (25) 173 (12) 0.003 (23) 0.200 (12)
SW6 0.99 (24) 0.82 (8) 4.80 (5) 0.59 (19) 0.56 (4) 0.19 (13) 0.25 (4) 2.34 (13) 119 (20) 0.010 (18) 0.117 (20)
SW7 1.02 (21) 0.74 (15) 4.48 (8) 0.91 (8) 0.85 (20) 0.14 (8) 0.57 (20) 2.72 (18) 146 (16) 0.009 (19) 0.149 (16)
SW8 1.07 (14) 0.87 (3) 4.35 (12) 0.83 (11) 0.84 (18) 0.21 (16) 0.55 (18) 2.22 (10) 136 (19) 0.014 (11) 0.145 (17)
SW9 1.16 (3) 0.94 (2) 3.74 (21) 1.09 (6) 0.88 (22) 0.25 (23) 0.61 (22) 2.01 (3) 94 (21) 0.009 (20) 0.109 (21)
SW10 0.94 (25) 0.71 (19) 3.17 (24) 0.70 (14) 0.77 (15) 0.24 (18) 0.47 (15) 2.04 (8) 137 (17) 0.013 (13) 0.129 (19)
SW11 1.01 (22) 0.78 (14) 3.11 (25) 0.89 (10) 0.88 (21) 0.18 (12) 0.61 (21) 2.37 (14) 167 (14) 0.014 (10) 0.169 (14)
SW12 1.04 (15) 0.95 (1) 3.98 (16) 1.23 (3) 0.92 (25) 0.25 (24) 0.66 (25) 2.00 (2) 137 (18) 0.012 (16) 0.143 (18)
SW13 1.03 (18) 0.49 (25) 3.50 (22) 0.50 (22) 0.65 (10) 0.25 (20) 0.33 (10) 2.02 (6) 211 (10) 0.017 (7) 0.217 (10)
SW14 1.11 (8) 0.84 (5) 4.47 (9) 0.90 (9) 0.80 (16) 0.24 (17) 0.50 (16) 2.08 (9) 214 (9) 0.020 (2) 0.237 (9)
SW15 1.07 (13) 0.82 (7) 4.31 (13) 0.69 (15) 0.64 (8) 0.15 (11) 0.32 (8) 2.59 (15) 248 (6) 0.018 (5) 0.265 (7)
SW16 1.09 (10) 0.61 (24) 4.45 (11) 0.62 (18) 0.61 (6) 0.21 (15) 0.29 (6) 2.22 (11) 251 (5) 0.017 (6) 0.273 (6)
SW17 1.14 (5) 0.85 (4) 3.45 (23) 1.29 (2) 0.91 (24) 0.25 (21) 0.65 (24) 2.02 (5) 173 (13) 0.013 (14) 0.197 (13)
SW18 1.02 (19) 0.80 (12) 5.20 (3) 0.63 (17) 0.70 (12) 0.09 (2) 0.38 (12) 3.33 (24) 153 (15) 0.010 (17) 0.157 (15)
SW19 1.13 (7) 0.62 (22) 3.75 (19) 0.67 (16) 0.65 (9) 0.25 (19) 0.33 (9) 2.04 (7) 261 (4) 0.019 (4) 0.295 (5)
SW20 1.03 (17) 0.74 (16) 4.47 (10) 0.98 (7) 0.89 (23) 0.32 (25) 0.62 (23) 1.79 (1) 205 (11) 0.019 (3) 0.211 (11)
SW21 1.36 (1) 0.72 (17) 4.14 (14) 0.56 (20) 0.589 (5) 0.14 (7) 0.27 (5) 2.74 (19) 223 (8) 0.016 (9) 0.304 (4)
SW22 1.02 (20) 0.61 (23) 6.44 (1) 0.47 (24) 0.41 (1) 0.09 (4) 0.13 (1) 3.29 (22) 300 (2) 0.012 (15) 0.307 (3)
SW23 1.07 (12) 0.78 (13) 3.75 (20) 0.46 (25) 0.43 (3) 0.09 (3) 0.14 (3) 3.30 (23) 241 (7) 0.013 (12) 0.258 (8)
SW24 1.09 (11) 0.68 (20) 4.03 (15) 0.80 (12) 0.67 (11) 0.14 (9) 0.36 (11) 2.70 (17) 308 (1) 0.016 (8) 0.335 (1)
SW25 1.18 (2) 0.80 (11) 3.91 (18) 1.10 (4) 0.81 (17) 0.25 (22) 0.52 (17) 2.01 (4) 267 (3) 0.020 (1) 0.315 (2)
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