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

Nwilo, Peter C.; Ogbeta, Caleb O.; Daramola, Olagoke E.; Okolie, Chukwuma J.; Orji, Michael J.

doi:10.2478/quageo-2021-0029

Figures & Tables

Map showing the location of the study area.

Drainage map of Imo River Basin showing the stream order.

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

Overlay of validation points on the erosion susceptibility map.

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)
Point no.	Location name	Erosion type	[mE]	[mN]	[m]	[km²]	Source(s)
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	Amangabara et al. (2015)
6	Umuahia North	Gully erosion	332166	617607	–	6.85–31.70	Channels Television (2018)
7	Aboh-Mbaise	Gully erosion	309726	593501	–	0.76–1.530	Channels Television (2018)
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
	Basin area	Basin perimeter	Basin length	No. of streams	Total stream length	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
Sub-watershed	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)

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

Figures & Tables

Fig. 1

Fig. 2

Fig. 3

Fig. 4

Fig. 5

Fig. 6

Fig. 7

Coordinates of the ROC curve_

Descriptive information of the validation points_

Pearson correlation matrix of sub-watershed morphometric parameters_

Watershed prioritisation and final ranking for erosion susceptibility_

Formulas adapted for the computation of morphometric parameters_

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

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

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