Quantitative analysis and implications of drainage morphometry of the Agula watershed in the semi-arid northern Ethiopia

Abstract

This study aimed at quantitative analysis of morphometric parameters of Agula watershed and its subwatersheds using remote sensing data, geographic information system, and statistical methods. Morphometric parameters were evaluated from four perspectives: drainage network, watershed geometry, drainage texture, and relief characteristics. A sixth-order river drains Agula watershed and the drainage network is mainly dendritic type. The mean bifurcation ratio (R b ) was 4.46 and at sub-watershed scale, high R b values (R b [ 5) were observed which might be expected in regions of steeply sloping terrain. The longest flow path of Agula watershed is 48.5 km, with knickpoints along the main river which could be attributed to change of lithology and major faults which are common along the rift escarpments. The watershed has elongated shape suggesting low peak flows for longer duration and hence easier flood management. The drainage texture analysis revealed fine drainage which implies the dominance of impermeable soft rock with low resistance against erosion. High relief and steep slopes dominates, by which rough landforms (hills, breaks, and low mountains) make up 76% of the watershed. The S-shaped hypsometric curve with hypsometric integral of 0.4 suggests that Agula watershed is in equilibrium or mature stage of geomorphic evolution. At sub-watershed scale, the derived morphometric parameters were grouped into three clusters (low, moderate, and high) and considerable spatial variability was observed. The results of this study provide information on drainage morphometry that can help better understand the watershed characteristics and serve as a basis for improved planning, management, and decision making to ensure sustainable use of watershed resources.

Physical Dynamics and the Influences of the Environment Built on Subbasins

“…2 shows the calculated geometric attributes for SB1 and SB2. These dimensions can be obtained [30,31] by considering the length of the main channel (river) and the axial length of subbasins. When considering geometric attributes, subbasins are influenced by sediment load, lithological compartmentalization, geologic structure and channel slope.…”

“…The development of this drainage system provides efficiency, as it expresses the relationship between the sum of the lengths of all channels of the network and the total basin area [18][19][20]30]. In this length [30], all channels, whether perennial, intermittent or temporary, are considered.…”

“…By analyzing the frequency of drainage network (Dr), texture ratio (T), hydrodynamic density (Dh) and drainage density (Dd) [16,[28][29][30][31] shown in Fig. 3, it can be observed that SB1 presents higher values due to a more accentuated relief caused by the flow and It is pointed out the need for integrative practices that aim to reduce the loss of soil, nutrients and water flow, as well as to considerably interfere in the dynamics of environmental components.…”

“…Data on drainage network, road system with curves of equidistance level of 20 m [25] were collected from the topographic map of IBGE (Brazilian Institute of Geography and Statistics), folios SF-23-YB-VI-3 (Pindamonhangaba) and SF-23-YD-III-1 (São Luiz do Paraitinga). In addition to this reference, numerical equations were used to obtain the results [16,[28][29][30][31]. …”

“…The ordering of channels from the entire morphometric data collection was performed by breaking down the network into discrete segment numbers, followed by the methodology described of first, second and third ordering of channels [16,[28][29][30][31].…”