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

Cheikh Faye
Cheikh Faye
 and 
Modou Ndiaye
Modou Ndiaye
   | Sep 30, 2021
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Published Online: Sep 30, 2021
Page range: 65 - 84
Received: May 22, 2021
DOI: https://doi.org/10.2478/quageo-2021-0024
Keywords
© 2021 Cheikh Faye et al., published by Sciendo
This work is licensed under the Creative Commons Attribution 4.0 International License.

Fig. 1

Location of the Soungrougrou basin.
Location of the Soungrougrou basin.

Fig. 2

Sub-basin division of the Soungrougrou basin.
Sub-basin division of the Soungrougrou basin.

Fig. 3

Order of the rivers in the Soungrougrou basin.
Order of the rivers in the Soungrougrou basin.

Fig. 4

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

Fig. 5

Land use in the Soungrougrou basin in 2000 and 2019.
Land use in the Soungrougrou basin in 2000 and 2019.

Fig. 6

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

Fig. 7

Prioritisation based on percentage change in land use categories between 2000 and 2019 for 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
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
Rb Dd Tj Fs Lo KG Rf Bs Rc Ra
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)
[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
[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
[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
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
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
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