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The present study attempts to examine the morphometric characteristics and relationships of 43 fourth-order sub-basins over the Zerqa River watershed, using ASTER DEM, GIS and multivariate statistics. To achieve these objectives, Principal Component Analysis was utilized to reduce the 26 parameters into six major components which accounted for 79.3% of the total variance explained by the original morphometric variables. Hierarchical Cluster Analysis (CA) (Ward’s method) has been applied to classify the 43 sub-basins based on different types of morphometric parameters. Four groups of sub-watersheds were identified and characterized by different morphometric properties. The patterns of spatial distribution of cluster groups were determined based on lithological, structure and tectonics, uplifting, and rejuvenation processes.

The Zerqa River watershed, locates in northern Jordan, and covers an area of 4031 km^{2}. At the lower catchment, the King Talal Reservoir (KTR) was constructed with a capacity of 56 MCM. Generally, the catchment area is highly vulnerable to soil erosion. The estimated sediment concentration for the Zerqa River ranges between 0.1% - 2.0%, and figures exceeding 3.0% were reported by the Natural Resources Authority [^{−1}, while Lara [^{−1}. Furthermore, the measured sediment inflow at King Talal reservoir (1980/1-1967/7), applying the AGNPS erosion model was found to be 2.9 and 2.456 MCM with and without landslides respectively [

Multivariate analysis of morphometric parameters and drainage basins of different orders, have been applied worldwide in geomorphic research [

1) Explore the relationships and correlations among morphometric variables which characterize the 43 forth- order sub-basins.

2) Describe the relationship of major components resulting from PCA to the morphometric variables, and to the individual sub-basing, and then to explain their contribution to the morphology of fourth-order sub-basins in the Zerqa River watershed.

3) Achieve a grouping scheme for the 43 sub-basins through Cluster Analysis (CA) by reference to their individual relationships to the components, and to the original morphometric parameters. The patterns of spatial distribution of cluster groups were analyzed in relation to lithology, tectonics and uplifting, and rejuvenation processes.

The study area (35˚32'42''E - 36˚48'9''E and 31˚51'37''N - 32˚35'4''N) comprises the Zerqa River watershed, northern Jordan. The catchment extends from the western highlands/the Ghor to the eastern desert, crossing the Jordanian-Syrian border until the piedmonts of Jebel el Druz northeast. The watershed is drained by two major tributaries: W. Dhulil and W. Zerqa which drain the eastern and western parts of the catchment respectively. Both wadis are joined at Shkhna town to form what is known as the “Zerqa River” (

Slope elements and segments of a watershed are often controlled by climato-morphogenetic processes [

Slope categories exhibited by the Zerqa River catchment vary from 0˚ to 20˚- 45˚. The slope categories map is illustrated in

The aspect of a land unit is the direction to which it faces. Aspect has a great impact on precipitation patterns, exposure to sun, wind, and hence evaporation rate, and vegetation type and density. Slopes facing the north, southeast, south, and southwest are predominant in the western part of the watershed (

The watershed is occupied by a sequence of rocks ranging from Triassic to recent sediments, whereas the nor

theastern part of the catchment is covered by basalt rocks ranging in age from Oligocene to Pleistocene. The geological succession in the watershed is illustrated in

Structurally, the western part of the Zerqa River catchment exhibits three major compressional structures locally termed: Wadi Shueib Structure, Biren Structure, and the Amman-Hallabat Structure (

Period | Epoch | Quennell [ | Bender [ | Thickness (m) |
---|---|---|---|---|

Tertiary and Quaternary | Pleistocene Holocene Pliocene-Eocene | Basalts, Unconsolidated Sediments, Mudflats, Lisan Marl, Fluviatile Gravel, and Infill Wadis. | ||

Upper Cretaceous | Santorian-Coniacian | Belqa | Chert-Limestone Silicified Limestone | 180 20 - 100 (Not Exposed) |

Turonian | Ajlune | Massive Limestone | 10 - 128 | |

Cenomarian | Echinoidal Limestone | 300 | ||

Nadular Limestone | 300 | |||

Lower Cretaceous | Albian Aptian Neocomian | Kurnub | Vari-Coloured Sandstone | 330 |

Jurassic Triassic | Zerqa | 500 |

Based on: [

The old landslide complex close to the Zerqa River bridge, and the Bassa landslide west of KTR are the best examples. The lower slopes of landslide complexes are considered an active landslide zone due to river incision, lateral erosion, recent tectonic activity [

The climate is of sub-humid Mediterranean in Suweileh and Jubba areas, then it shifts to semi-arid in the Baq’a depression and Jerash area, and dominated by arid conditions along the eastern part of the watershed. The climate is generally characterized by long, hot and dry summers, and relatively short and wet winters [^{th}, 1983 caused dozens of shallow landslides in Suweilh-Jerash area. The average annual stream flow of the Zerqa River is 70.3 MCM at KTR. Of that amount, storm runoff contributes 50.1 MCM, and the base flow represents 20.2 MCM [^{3}/s and many severe floods were recorded, during which peak flows occasionally approximated 400% of the mean maximum discharge. Examples of severe floods are those that occurred in 1935/1936, 1973/1974, 1979/1980 and 1983/1984 [

Topographic maps of scale 1:50,000 (20 m contour interval) were purchased from the Royal Jordanian National Geographic Centre (RJNGC), Amman. They were then scanned, geo-referenced, and converted to WGS-1984, zone 36˚N projection system using Arc GIS tool (v. 10.1) and the accompanying packages. The entire Zerqa River watershed and the 43 sub-basins were delineated initially using topo sheets. ASTER DEM (30 m spatial resolution) was employed to delineate the final boundaries of the Zerqa River watershed and the 43 sub-basins (_{u}), mean bifurcation ratio (R_{bm}), area (A), perimeter (P), basin length (L_{b}), elongation ration (R_{e}), drainage texture (D_{t}), texture ratio (T_{r}), circularity ratio (R_{c}), compactness coefficient (C_{c}), shape index (B_{s}), lemniscates ratio (k), stream frequency (F_{s}), drainage density (D_{d}), form factor (R_{f}),drainage intensity (D_{i}), constant of channel maintenance (C), length of overland flow (L_{o}), basin relief (B_{h}), relief ratio (R_{r}), ruggedness number (R_{n}), dissection index( D_{is}), time of concentration (T_{c}).

Multivariate statistical techniques were also employed in the present study. Principal Component Analysis (PCA), and Cluster Analysis (CA) have been utilized since the early 1970s in drainage morphometric research [

Quantitative analysis was performed for the entire Zerqa River watershed and the 43 sub-basins in order to

Morphometric parameters | Formula/Definition | References |
---|---|---|

I. Drainage network | ||

1. Stream order (u) | Hierarchical rank | [ |

2. No. of streams (N_{u}) | [ | |

3. Stream length (L_{u}) km | [ | |

4. Mean stream length (L_{sm}) km | L_{sm} = L_{u}/N_{u} (km) | [ |

5. Stream length ratio (R) | R_{L} = L_{u}/L_{u − 1}, where L_{u} = the total stream length of order “u”, L_{u − 1} = the total stream length of its next lower order. | [ |

6. Bifurcation ratio (R_{b}) | R_{b} = N_{u}/N_{u + 1}, where N_{u} = total no. of tream segment of order “u”, N_{u + 1} = no. of segments of the next higher order. | [ |

7. Mean bifurcation ratio (R_{bm}) | R_{bm} = average of bifurcation ratio of Strahler all orders. | [ |

II. Basin geometry | ||

8. Basin length (L_{b}) km | Length of the basin (km) | [ |

9. Basin area (A) km^{2} | Plan area of the watershed (km^{2}) | [ |

10. Mean basin width (W_{b}) | W_{b} = A/L | [ |

11. Basin perimeter (P) km | Perimeter of the watershed (km) | [ |

12. Form factor (ratio) (R_{f}) | R_{f} = A/L_{b}^{2} | [ |

13. Elongation ratio (R_{e}) | R_{e} = | [ |

14. Compactness coefficient (C_{c}) | C_{c} = 0.2841 * P/A^{0.5} | [ |

15. Texture ratio (T_{r}) | Tr = N_{1}/P | [ |

16. Shape index (B_{s}) | Bs = L_{b}^{2}/A | [ |

17. Lemniscate ratio (k) | k = L^{2}/4A | [ |

18. Circularity ratio (R_{c}) | R_{c} = | [ |

19. Drainage texture (D_{t}) | Dt = N_{u}/P, where Nu = Total no. of streams ofall orders, P = perimeter (k) | [ |

III. Drainage texture analysis | ||

20. Stream frequency (F_{s}) | F_{s} = N_{u}/A | [ |

21. Drainage density (D_{d}) km/km^{2} | D_{d} = L_{u}/A | [ |

22. Drainage intensity (D_{i}) | D_{i} = F_{s}/D_{d} | [ |

23. Constant channel maintenance (C) km^{2}/km | C = 1/D_{d} | [ |

24. Length of overland flow (L_{o}) km | L_{o} = 1/2D_{d} | [ |

IV. Relief characteristics | ||

25. Basin relief (B_{h}) or total relief (H) m | B_{h} = h − h_{1}, where, h = maximum height (m) h_{1} = minimum height (m) | [ |

26. Relief ratio (R_{r}) | R_{r} = H/L_{b}, Where H = total relief L_{b} = basin length | [ |

27. Ruggedness number (R_{n}) | R_{n} = D_{d} * (B_{h}/1000) | [ |

28. Dissection index (D_{is}) | D_{is} = B_{h}/R_{a}, where R_{a} = absolute relief | [ |

29. Time of concentration (T_{c}) | T_{c} = 6.95 (L^{1.15}/B_{s}^{0.385}) | [ |

where L = length of main stream |

assess the characteristics and properties of the drainage networks. Twenty-six morphometric parameters which representing drainage network, basin geometry, drainage texture analysis, and relief characteristics were considered to characterize the catchment and to enhance our understanding of drainage basin development in relation to intrinsic controlling factors, such as lithology, tectonic and structure, geomorphic processes and rejuvenation phases. _{u}) is 5806, and the first-order streams account for 79.6% of the total number of streams in the watershed. It is noticeable that the total number of streams gradually decreases as the stream order increases (

Generally, the higher the order is, the longer the length of stream in nature is. The total stream length (L_{u}) of the Zerqa River is 7148.25 km, and the first-order streams represent 48.5% of the total stream length. A variation exists in (R_{L}) values between the streams for different order of the Zerqa River watershed (0.376 - 3.4), and the 43 sub-basins. This variation might be attributed to geomorphic changes in relief and slope along the Zerqa Rive, the influence of the compressional structures, the stage of geomorphic development, and rejuvenation along the catchment.

The value of bifurcation ratios for the Zerqa River watershed and the 43 sub basins are typical for catchments in which structural disturbances distort the drainage system (R_{b} varied from 2.7 to 5.002, with a mean of 4.9). The main morphological factors controlling drainage density (D_{d}) are relative relief and slope steepness. Low drainage density is realized where the catchment relief is high [_{d} are: the resistance of surface materials against erosion, and the infiltration-capacity of the soil. The D_{d} value for the Zerqa River watershed is 1.46 which indicates a moderate to well-drained basin. The presence of dissected and steep slopes with relatively impervious underlying bedrock, i.e., the nodular limestone (marly-clay unit), and the Echinoidal limestone (limestone-marly unit) exposed at the middle part of the watershed resulted in a series of springs out flowing to the major courses of the river. According to Smith [_{t}), where the D_{t} value is 15.383. High drainage texture values denote the presence of fragile slope materials and soft rocks where high sediment yield has been recorded [_{s} value for the Zerqa River watershed is 1.186, and for the 43 sub-basins range from 0.979 to 6.133. Low F_{s} values indicate that a relatively low infiltration rate of surface water is assumed, therefore, the groundwater potential is relatively low. Strahler [_{e}) vary between 0.6 to 1.0 over a wide range of geological and climatic conditions. The elongation ratio (R_{e}) for the Zerqa River catchment is 0.548, where the values related to the 43 sub-basins range from 0.170 to 1.234. Such values are indicative of elongated shape, and are associated with high relief and steep valley-side slopes. According to Miller [_{c}) of 0.4 to 0.5 are described as strongly elongated and at the youth stage of geomorphic development. The R_{c} value of the Zerqa River basin is 0.284, and the form factor (R_{f}) value is 0.236. Low R_{f} value denotes that low peak flows of long duration are expected for the Zerqa River watershed [

The basin relief (B_{h}) of the Zerqa River watershed is 1949 m. High B_{h} value indicates a high potential erosional energy of the drainage system. Due to repetitive sinking and changes in the base level of the Dead Sea and the Ghor (along the Jordan River), and tectonic activity, the Zerqa River retained rapid downcutting and incision through its geomorphic history, giving, rise to the present dissected and rough terrain. High rates of annual soil loss and landslide movements are noticeable geomorphic processes at present. The dissection index (D_{i}) value for the Zerqa River basin is 0.812 which clearly shows that the watershed is extremely dissected as a result of recurrent phases of rejuvenation, and youth-age stage of geomorphic evolution, where the hypsometric integral is found to be 0.834 (_{i} value and the classification of drainage basins in terms of dissection, the Zerqa River watershed is considered highly dissected (0.7 - 1.0) [_{n}) f or the Zerqa River basin is 2.845 which affirms an extreme morphological appearance. High R_{n} value is indicative of active geomorphic processes due to rejuvenation. Furthermore, the lemniscates (k) value for the Zerqa River watershed is 1.056 which illustrates that the basin is elongated and flows for a longer duration. The related hypsometric curve is a convex upward one, and the hypsometric integral is 0.834, denoting that the Zerqa River is in the youth-age stage of geomorphic development, and subjected to tectonic activity and rejuvenation. Therefore, dissected and rugged landscape, and landslide activity are characteristic of the western part of the watershed.

Morphometric parameters | Stream | Order | |||||
---|---|---|---|---|---|---|---|

I. Drainage network | |||||||

1.Stream order (u) | I | II | III | IV | V | VI | VII |

2. No. of streams (N_{u}) 4001 | 4623 | 919 | 198 | 50 | 11 | 4 | 1 |

3. Stream length (L_{u}) km 5931.4 | 3468.7 | 1885.9 | 980.3 | 467.1 | 175.9 | 91.1 | 109.3 |

4. Mean stream length (L_{sm}) km 0.998 | 0.750 | 2.1 | 4.95 | 9.34 | 15.99 | 22.8 | 109.32 |

5. Stream length ratio (R_{L}) | II/I | III/II | IV/III | V/IV | IV/V | IV/VII | |

6. Bifurcation ratio (R_{b}) | 0.503 | 0.528 | 0.467 | 0.367 | 0.518 | 1.2 | |

II/I | III/II | IV/III | IV/V | V/IV | IV/VII | ||

5.0 | 4.64 | 3.96 | 4.55 | 2.75 | 4.0 | ||

7. Mean bifurcation ratio (R_{bm}) | 4.897 | ||||||

II. Basin geometry | |||||||

8. Basin length (L_{b}) km | 143.834 | ||||||

9. Basin area (A) km^{2} | 4895.112 | ||||||

10. Basin perimeter (P) km | 464.68 | ||||||

11. Form factor (ratio) (Rf) | 0.236 | ||||||

12. Elongation ratio (Re) | 0.530 | ||||||

13. Compactness coefficient (C_{c}) | 1.87 | ||||||

14. Texture ratio (Tr) | 1.463 | ||||||

15. Shape factor (B_{s}) | 4.52 | ||||||

16. Lemniscate ratio (k) | 1.06 | ||||||

17. Circularity ratio (R_{c}) | 0.284 | ||||||

18. Drainage texture (D_{t}) | 9.9 | ||||||

III. Drainage texture analysis | |||||||

19. Stream frequency (F_{s}) | 1.186 | ||||||

20. Drainage density (D_{d}) | 1.477 | ||||||

21. Drainage intensity (D_{i}) | 0.812 | ||||||

22. Constant channel maintenance (C) | 0.73 | ||||||

23. Length of overland flow (L_{O}) km | 0.730 | ||||||

IV. Relief characteristics | |||||||

24. Basin relief (B_{h}) m | 1949 | ||||||

25. Relief ratio (R_{r}) | 0.013 | ||||||

26. Ruggedness number (R_{n}) | 2.845 | ||||||

27. Dissection index (D_{is}) | 1.231 | ||||||

28. Time of concentration (T_{c}) | 13.4 | ||||||

29. Hypsometric integral (H_{i}) | 0.834 |

_{s}) and drainage density (D_{d}), elongation ratio (R_{e}) and stream length ratio (R_{L}); and constant channel maintenance (C) and mean stream length (L_{sm}). _{b}; R_{e} and R_{c}; L_{o} and R_{f}’ (C and Di). Good correlations (R = 0.7 − 0.8) exist mainly between (P) and (A); (R_{c}) and (T_{r}); (D_{d}) and (F_{s}); (R_{r} and B_{h}). Moderately well correlated parameters (R = 0.5 − 0.7) include (R_{L} and L_{u}); (P and R_{L}); (R_{b} and L_{sm}); (T_{r}_{ }and R_{b}); (L_{b} and R_{L}); (k and C_{c}). Principal Component Analysis was carried out considering these correlation levels, because the correlation of the significant components takes into account the level and directions (negative or positive) of correlation [

Principal Component Analysis resulted in six major components that accounted for 79.3% of the total variance explained by the original 26 morphometric variables (_{L}, R_{b}, A, P, L_{b}, T_{r}, R_{f}, R_{e}, B_{s}, C_{c} and k), and drainage texture (D_{d} and L_{o}) morphometric parameters. These components together explain 64.5% of the total variance, whereas the fifth and sixth components represent basin geometry (T_{r} and R_{c}) and relief characteristics (B_{h} and R_{r}) morphometric parameters. However, the contributions of PC4 and PC5 are noticeably smaller than those of

Para. | Mean | Std. Deviation |
---|---|---|

L_{u} | 7.924 | 2.529 |

L_{sm} | 1.565 | 0.659 |

R_{L} | 0.154 | 0.083 |

R_{b} | 3.057 | 1.741 |

A | 1.782 | 13.201 |

P | 4.515 | 18.957 |

L_{b} | 1.507 | 6.857 |

W_{b} | 5.213 | 18.436 |

B_{s} | 1.644 | 9.749 |

R_{f} | 0.103 | 0.175 |

R_{e} | 0.325 | 0.161 |

D_{t} | 1.229 | 0.687 |

T_{r} | 0.636 | 0.293 |

R_{c} | 0.120 | 0.125 |

C_{c} | 6.626 | 1.854 |

K | 4.112 | 2.436 |

F_{s} | 2.069 | 1.122 |

D_{d} | 2.513 | 1.696 |

D_{i} | 1.162 | 0.822 |

C_{c} | 0.748 | 0.717 |

L_{o} | 0.594 | 0.462 |

B_{h} | 2.291 | 171.034 |

R_{r} | 1.616 | 11.987 |

R_{n} | 4.054 | 288.454 |

D_{is} | 0.7950 | 2.284 |

T_{c} | 1.543 | 0.538 |