Use of Geospatial Tools in Morphometric Analysis and Prioritisation of Sub-catchments of the Soungrougrou (Casamance Basin)

Cheikh Faye; Modou Ndiaye

doi:10.2478/quageo-2021-0024

Figures & Tables

Sub-basin division of the Soungrougrou basin.

Order of the rivers in the Soungrougrou basin.

Digital elevation model and slope [%] of the Soungrougrou sub-basin.

Land use in the Soungrougrou basin in 2000 and 2019.

Prioritisation based on morphometric analysis of the Soungrougrou sub-catchments.

Prioritisation based on percentage change in land use categories between 2000 and 2019 for the Soungrougrou sub-catchments.

Morphometric parameters_

Morphometric parameters	Descriptions	References
Linear aspects
Stream number (Nu)	Nu = N1 + N2 + ... Nn; where, Lu = Length of the river, L1 = Length of the first-order river and L2 = Length of the second-order river and Ln = Number ‘n’ of the river length.	Strahler (1964)
Stream length (Lu)	Lu = L1 + L2......; where, N1 = First-order river, N2 = Second-order river and Nn = Number of rivers	Strahler (1964)
Average length of flow (Lum)	Lum = Lu/Nu; where, Lu = Length of rivers of a given order (km), Nu = Number of river segments.	Strahler (1964)
Flow length ratio (Lur)	Lur = Lu/Lu−1; where, Lu = Total length of the rivers of order (u), Lu−1 = Total length of the rivers of the next lower order.	Strahler (1964)
Bifurcation ratio (Rb)	Rb = Nu/Nu + 1; where, Nu = Number of river segments present in the given order, Nu + 1 = Number of segments in the next higher order.	Schumm (1956)
Drainage density (Dd)	Dd = L/A; where, L = Total length of the river, A = Area of the basin.	Strahler (1964)
Drainage texture (Tj)	Tj = Dd*Nj/A, where Tj = Torrentiality coefficient of the order flow; Nj = Number of streams of order j, A = Basin area, Dd = Drainage density (km × km⁻²).	Strahler (1964)
Flow frequency (Fs)	Fs = N/A; where, L = Total number of rivers, A = Area of the basin	Strahler (1964)
Length of surface flow (Lo)	Lo = 1/2Dd, where, Dd = Drainage density	Strahler (1964)
Texture ratio (Rt)	Rt = N1/P; where, N1 = Total number of first-order rivers, P = Basin perimeter	Strahler (1964)
Formal aspects
Gravelius Compactness Coefficient (KG)	(KG) = 0.25P/ÖA; where KG = Gravelius compactness coefficient, P = Basin perimeter, A = Basin area	Gravelius (1914)
Form factor (Ff)	Ff = A/(Lb)^2; where, A = Area of the basin, Lb = Length of the basin	Strahler (1964)
Basin shape (Bs)	Bs = Lb^2/A; where A = Area of the basin, Lb = Length of the basin	Chorley (1957)
Form factor (k)	k = Lb^2p/4A; where A = Area of the basin, p = 3.14, Lb = Length of the basin	Chorley (1957)
Circularity ratio (Rc)	Rc = 4pA/P^2; where A = Area of the basin, p = 3.14, P = Perimeter of the basin.	Miller (1953)
Elongation ratio (Ra)	Ra = Ö(A/p)/Lb; where, A = Area of the basin, p = 3.14, Lb = Length of the basin	Schumm (1956)
Constant channel maintenance (C)	C = 1/Dd, where, Dd = Drainage density	Strahler (1964)
Terrain aspects
Basin relief (Rh)	Vertical distance between the lowest and highest point of the pool	Schumm (1956)
Relief ratio (Rhl)	Rhl = Bh/Lb; where, Bh = Basin relief, Lb = Basin length	Schumm (1956)
Relative relief (Rr)	Rr = Rh*100/P, where Rh = Basin relief, P = Basin perimeter.	Umair and Syed (2014)
Robustness number (Rn)	Rn = Bh ′ Dd; where, Bh = Basin relief, Dd = Drainage density	Schumm (1956)
Slope (m)	m = Dy/Dx or Rise/Run where, m = Slope, Dy is a vertical change, Dx is a horizontal change	Todhunter (1888)

Current analysis of the sub-catchments of the Soungrougrou catchment_

Sub-basins	Number of flows (Nu)					Length of watercourse (Lu)					Length ratio
Sub-basins	1	2	3	4	5	1	2	3	4	5	2/1	3/2	4/3	5/4
SB1	217	100	65	45	6	340.30	144.10	95.22	62.45	8.04	0.92	1.02	0.95	0.97
SB 2	71	33	19	18	–	104.10	70.24	27.63	20.00	–	1.45	0.68	0.76	–
SB 3	7	5	11	–	–	11.68	11.48	2.14	–	–	1.38	0.93	–	–
SB 4	4	3	–	–	–	6.73	9.73	–	–	–	1.93	–	–	–
SB 5	4	3	–	–	–	4.43	8.39	–	–	–	2.53	–	–	–
SB 6	6	3	12	–	–	11.01	1.89	6.06		–	0.34	4.81	–	–
SB 7	34	22	17	14	–	38.08	28.68	9.31	7.77	–	1.16	1.02	1.46	–
SB 8	9	8	–	–	–	13.15	12.42	–	–	–	1.06	–	–	–
SB 9	12	5	6		–	13.04	5.23	9.24	–	–	0.96	1.47	–	–
SB 10	8	7	–	–	–	12.28	8.13	–	–	–	0.76	–	–	–
SB 11	28	17	16	14	–	33.30	27.30	7.30	5.17	–	1.35	0.76	1.06	–
SB 12	44	22	14	17	–	48.80	35.80	21.40	6.68	–	1.47	0.94	0.62	–
SB 13	33	14	15	14	–	44.40	26.40	7.29	13.20	–	1.40	0.77	0.65	–
SB 14	20	11	15	–	–	27.30	10.20	8.49	–	–	0.68	1.83	–	–
SB 15	7	4	11	–	–	13.00	6.15	0.98	–	–	0.83	0.64	–	–
SB 16	8	5	–	–	–	9.35	12.20	–	–	–	2.08	–	–	–
SB 17	20	13	14	–	–	19.10	18.60	9.22	–	–	1.50	1.61	–	–
SB 18	46	25	17	–	–	53.30	34.40	18.80	–	–	1.19	0.80	–	–
SB 19	82	44	12	25	–	118.00	58.20	16.00	24.40	–	0.92	1.01	0.73	–
SB 20	9	7	–	–	–	11.80	5.20	–	–	–	0.57	–	–	–

Shape parameters of the sub-catchments of the Soungrougrou catchment_

Sub-basins	Form factor (k)	Constant channel maintenance (C)	Gravelius Compactness Coefficient (KG)	Form factor (Ff)	Basin shape (Bs)	Circularity ratio (Rc)	Elongation ratio (Ra)
SB 1	2.111	2.100	2.086	0.372	2.689	0.226	2.679
SB 2	2.369	2.295	2.189	0.331	3.018	0.205	2.034
SB 3	2.297	2.444	1.676	0.342	2.926	0.350	1.210
SB 4	2.055	2.777	1.790	0.382	2.618	0.307	1.154
SB 5	2.250	2.566	1.700	0.349	2.866	0.341	1.039
SB 6	1.987	1.857	1.557	0.395	2.531	0.406	1.090
SB 7	1.200	1.991	1.911	0.654	1.528	0.270	1.824
SB 8	2.048	1.986	1.794	0.383	2.608	0.306	1.185
SB 9	1.742	2.055	1.710	0.451	2.219	0.337	1.268
SB 10	2.006	2.105	1.575	0.391	2.556	0.397	1.143
SB 11	1.411	2.169	1.795	0.556	1.798	0.306	1.729
SB 12	1.180	2.044	1.866	0.665	1.503	0.283	1.985
SB 13	1.600	2.061	1.917	0.491	2.038	0.268	1.749
SB 14	1.943	1.967	1.699	0.404	2.475	0.341	1.387
SB 15	1.568	2.277	1.518	0.501	1.997	0.427	1.235
SB 16	1.873	2.401	1.640	0.419	2.386	0.366	1.217
SB 17	1.520	1.984	1.500	0.516	1.937	0.438	1.485
SB 18	1.887	1.899	1.866	0.416	2.403	0.283	1.709
SB 19	2.058	1.872	2.005	0.381	2.622	0.245	1.989
SB 20	1.603	2.361	1.797	0.490	2.042	0.305	1.189

Linear parameters of the sub-catchments of the Soungrougrou catchment_

Sub-basins	Stream number (Nu)	Stream length (Lu)	Flow length ratio (Lur)	Bifurcation ratio (Rb)	Drainage density (Dd)	Drainage texture (Tj)	Flow frequency (Fs)	Length of surface flow (Lo)
SB 1	433	650.11	0.962	3.163	0.476	0.151	0.317	0.238
SB 2	141	221.97	0.966	1.648	0.436	0.121	0.277	0.218
SB 3	13	25.30	1.154	3.200	0.409	0.086	0.210	0.205
SB 4	7	16.46	1.928	1.333	0.360	0.055	0.153	0.180
SB 5	7	12.82	2.525	1.333	0.390	0.083	0.213	0.195
SB 6	11	18.96	2.576	1.750	0.538	0.168	0.312	0.269
SB 7	67	83.84	1.215	2.146	0.502	0.202	0.401	0.251
SB 8	17	25.57	1.063	1.125	0.503	0.169	0.335	0.252
SB 9	23	27.51	1.217	1.617	0.487	0.198	0.407	0.243
SB 10	15	20.41	0.757	1.143	0.475	0.166	0.349	0.237
SB 11	55	73.06	1.057	1.993	0.461	0.160	0.347	0.230
SB 12	87	112.61	1.010	1.857	0.489	0.185	0.378	0.245
SB 13	66	91.26	0.941	1.838	0.485	0.170	0.351	0.243
SB 14	36	45.92	1.257	2.009	0.508	0.203	0.399	0.254
SB 15	12	20.10	0.734	2.875	0.439	0.115	0.262	0.220
SB 16	13	21.51	2.081	1.600	0.417	0.105	0.252	0.208
SB 17	37	46.87	1.555	2.394	0.504	0.201	0.398	0.252
SB 18	88	106.52	0.996	1.655	0.527	0.229	0.435	0.263
SB 19	163	216.01	0.887	2.003	0.534	0.215	0.403	0.267
SB 20	16	17.03	0.565	1.286	0.424	0.169	0.398	0.212

Results of the prioritisation of the morphometric analysis of the Soungrougrou sub-catchments_

Sub-basins	Linear parameters					Shape parameters					Cp value	Final priority
Sub-basins	Rb	Dd	Tj	Fs	Lo	KG	Rf	Bs	Rc	Ra	Cp value	Final priority
SB 1	2	11	14	13	11	19	7	17	2	20	11.6	Low
SB 2	13	15	15	15	15	20	1	20	1	19	13.4	Low
SB 3	1	18	18	19	18	6	2	19	15	7	12.3	Medium
SB 4	16	20	20	20	20	10	6	15	11	1	13.9	Medium
SB 5	17	19	19	18	19	8	3	18	13	1	13.5	Medium
SB 6	11	1	11	14	1	3	9	12	18	2	8.2	High
SB 7	5	7	4	4	7	16	19	2	5	16	8.5	Medium
SB 8	20	6	10	12	6	11	7	14	10	5	10.1	High
SB 9	14	9	6	2	9	9	13	8	12	10	9.2	Medium
SB 10	19	12	12	10	12	4	8	13	17	3	11.0	Medium
SB 11	8	13	13	11	13	12	18	3	9	14	11.4	Medium
SB 12	9	8	7	8	8	14	20	1	7	17	9.9	Medium
SB 13	10	10	8	9	10	17	15	6	4	15	10.4	Medium
SB 14	6	4	3	5	4	7	10	11	14	11	7.5	High
SB 15	3	14	16	16	14	2	16	2	19	9	11.1	Medium
SB 16	15	17	17	17	17	5	12	9	16	8	13.3	Medium
SB 17	4	5	5	7	5	1	17	4	20	12	8.0	High
SB 18	12	3	1	1	3	15	11	10	6	13	7.5	High
SB 19	7	2	2	3	2	18	5	16	3	18	7.6	Medium
SB 20	18	16	9	6	16	13	14	7	8	6	11.3	Medium

Aspect parameters related to the relief of the Soungrougrou sub-catchments_

Sub-basins	Basin relief (Rh)	Relief ratio (Rhl)	Relative relief (Rr)	Robustness number (Rn)
Sub-basins	[m]	[m m⁻¹]	[%]	[−]
SB 1	55	0.001	0.020	0.026
SB 2	50	0.001	0.028	0.022
SB 3	48	0.004	0.102	0.020
SB 4	44	0.004	0.102	0.016
SB 5	51	0.005	0.146	0.020
SB 6	50	0.005	0.152	0.027
SB 7	49	0.003	0.056	0.025
SB 8	52	0.005	0.114	0.026
SB 9	51	0.005	0.111	0.025
SB 10	46	0.004	0.125	0.022
SB 11	56	0.003	0.069	0.026
SB 12	56	0.003	0.055	0.027
SB 13	54	0.003	0.058	0.026
SB 14	51	0.003	0.088	0.026
SB 15	48	0.005	0.131	0.021
SB 16	50	0.005	0.119	0.021
SB 17	49	0.004	0.095	0.025
SB 18	55	0.002	0.058	0.029
SB 19	54	0.002	0.038	0.029
SB 20	50	0.006	0.123	0.021

Area land use in 2000 and 2019_

Land use	2000		2019		Balance sheet
Land use	[km²]	[%]	[km²]	[%]	[km²]	[%]
Cultivated areas and bare soil	892	18.6	1036	21.6	144	3.0
Open woodland	2719	56.7	2291	47.8	−428	−8.9
Very open woodland	933	19.5	1151	24.0	217	4.5
Water surface	83	1.7	112	2.3	29	0.6
Other	164	3.4	202	4.2	38	0.8
Total	4791	100.0	4791	100.0	–	–

Matrix of land use changes between 2000 and 2019_

Classes	Cropland and bare ground	Open woodland	Very open woodland	Water	Tannes and burn	Losses
Classes	[km²]
Cropland and bare ground	528.00	140.00	189.00	1.00	33.90	364.00
Open woodland	230.00	1917.00	534.00	0.24	37.30	802.00
Very open woodland	247.00	229.00	392.00	0.09	65.20	541.00
Water	0.29	0.15	0.10	79.60	2.93	3.47
Tannes and burn	30.40	4.40	35.50	31.00	63.00	101.00
Earnings	507.00	374.00	759.00	32.50	139.00	–

Results of prioritisation of area change in land use categories between 2000 and 2019 for the Soungrougrou sub-catchments_

Sub-basins	Absolute value of the percentage difference in land use area between 2019 and 2000				Prioritisation of land use change [%]				Cp value	Final priority
Sub-basins	Cropped areas and bare soil	Open woodland	Very open woodland	Tannes and burnt land	Cropped areas and bare soil	Open woodland	Very open woodland	Tannes and burnt land	Cp value	Final priority
SB 1	14.81	13.67	4.05	3.64	2	6	3	1	3.00	High
SB 2	2.82	11.11	14.67	0.73	16	20	1	2	9.75	Medium
SB 3	4.35	0.50	4.74	0.10	13	17	2	10	10.50	Medium
SB 4	6.10	8.23	1.31	0.83	12	10	5	5	8.00	Medium
SB 5	8.05	9.24	1.43	0.24	10	8	6	14	9.50	Medium
SB 6	7.03	8.43	1.59	0.23	11	9	7	13	10.00	Medium
SB 7	12.97	45.97	32.30	0.69	4	1	20	7	8.00	Medium
SB 8	12.95	13.56	1.06	0.49	5	7	4	17	8.25	Medium
SB 9	3.93	21.12	18.59	0.21	14	3	16	11	11.00	Medium
SB 10	0.46	23.80	23.14	0.91	10	2	19	4	8.75	Medium
SB 11	8.39	13.80	5.63	0.24	9	5	9	15	9.50	Medium
SB 12	2.80	16.48	19.17	0.11	17	4	17	8	11.50	Medium
SB 13	2.37	4.46	2.74	0.35	18	16	8	16	14.50	Low
SB 14	10.42	1.60	9.24	0.04	6	18	11	9	11.00	Medium
SB 15	14.71	7.53	21.27	2.71	3	12	18	2	8.75	Medium
SB 16	2.86	7.46	10.49	0.21	15	13	13	12	13.25	Low
SB 17	1.46	7.66	9.68	0.60	19	11	12	19	15.25	Low
SB 18	9.70	2.15	7.46	0.76	7	19	10	20	14.00	Low
SB 19	8.76	5.42	14.32	0.50	8	14	15	18	13.75	Low
SB 20	24.54	5.04	13.68	1.77	1	15	14	3	8.25	Medium

Use of Geospatial Tools in Morphometric Analysis and Prioritisation of Sub-catchments of the Soungrougrou (Casamance Basin)

Figures & Tables

Fig. 1

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Fig. 5

Fig. 6

Fig. 7

Morphometric parameters_

Current analysis of the sub-catchments of the Soungrougrou catchment_

Shape parameters of the sub-catchments of the Soungrougrou catchment_

Linear parameters of the sub-catchments of the Soungrougrou catchment_

Results of the prioritisation of the morphometric analysis of the Soungrougrou sub-catchments_

Aspect parameters related to the relief of the Soungrougrou sub-catchments_

Area land use in 2000 and 2019_

Matrix of land use changes between 2000 and 2019_

Results of prioritisation of area change in land use categories between 2000 and 2019 for the Soungrougrou sub-catchments_

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