Watershed morphometric analysis of a basin is key to understand the hydrological processes. The Gilgit river basin is situated in the Hindu Kush and Karakoram Mountains of Pakistan. The provincial capital of Gilgit-Baltistan is located in the lower part of the basin. Morphometric evaluation of the Gilgit river basin was carried out to study its drainage characteristics and overall water resource potential. The entire Gilgit river basin has been divided into six sub-basins to calculate and analyze the selected morphometric parameters. Morphometric parameters have been classified into linear, aerial and relief aspect. Geographic Information System (GIS) provides a viable method to extract and evaluate the characteristic of hydrological response behaviour of the basin. In the present study the utilization of remote sensing data such as Thermal Topography Mission and Global Elevation Model (ASTER-GDEM), Sentinel 2A image, coupled with geological and field data into GIS environment for morphometric analysis of Gilgit Basin. The drainage area of the basin is 13,538 km 2 and shows a dendritic drainage pattern for all sub-basins. The analysis reveals that drainage network of entire Gilgit river basin constitutes a 7 th order basin. Out of six sub-basins, Gilgit-Gahkuch (B1), Ishkoman (B2) and Phunder (B4) are 6 th order sub-basins. Yasin (B3) and Gupis (B5) are 5 th order sub-basins, while Bagrot (B6) is a 4 th order sub-basin. The Gilgit Basin drainage density value is 0.50 km/km 2, which indicates a well-drained basin. Morphometric parameters like stream number, order, length, bifurcation ratio, drainage density, stream frequency, elongation ratio, circularity ratio, form factor, relief and relative relief, slope, length of overland flow, ruggedness number, and hypsometric integral are calculated. The results indicate that the entire drainage basin area reflects youthful to early mature stage of the fluvial geomorphic cycle and high potential of stream discharge which is dominated by high relief, rainfall, glacier and snow fed order streams.
The natural structure of any drainage basin and its fluvial developments can be expressed in a quantitative way, and it can be analyzed through measurement of aerial, linear and relief aspect [
Morphometric analysis has been used for quantitative measurement of a particular characteristic of an area tectonic activity, morphometric indices, erosional and depositional processes. Gardiner (1990) [
Over the last few decades, Satellite data and GIS techniques have been providing a viable platform for assessing topography and morphometric factors of a drainage system [
Therefore, morphometric analysis of the watershed is important in understanding the hydrology of the watershed for sustainable use of natural resource as well as effective management of water induced disasters in mountainous areas. The present study aims at using the remote sensing and GIS technology to compute various parameters of morphometric characteristic of the Gilgit River Basin.
The Gilgit river basin (
The Ghizer road and a part of Karakoram High (KKH) is located in the studied area, these roads heavily used by millions of people annually, which underlines its significance in connecting this rugged landscape to the mainland, as well as the people who live in the valleys of Gilgit watershed which is the only access to south parts of the country from the north side. Ghizer road represents the
only highway connecting the Ghizer valley with Gilgit city and Chitral district of Khybar Pakhtunkhwa province of Pakistan (from east). Major and minor roads and several villages have been the subject of flash floods once or twice annually, especially in the monsoon season.
In the current research, different types of data have been used which includes: 1) Advanced Spaceborn Thermal Topography Mission and Global Elevation Model (ASTER-GDEM) data, with 30 m spatial resolution. 2) Geological maps, 3) field data and reconnaissance. Arc ArcGIS 10.2.2 used to obtaining a deeper understanding of the drainage system in the study area. Terrain pre-processing has been used in the processing and creating the watershed basin of the study area. In
The results of different morphometric parameters are listed in
The total area of Gilgit basin is 13,538 km2 and areas of sub-basins are presented in
Horton devised a quantitative method to analyzing drainage basins which have become a standard technique for presenting data on drainage basins. It is based upon a hierarchy of stream ordering which was revised by Strahler such as fingertip tributaries are first order stream, two first orders combine to form a second order, two second order form a third and so on. Drainage morphology of major and minor basin in many areas of the world have been studied using conventional geomorphologic approaches [
Stream order (U) refers to hierarchical link between the individual stream fragments than make up a drainage network. According to Horton’s principle the number of streams is negatively correlated with the order such as stream number
Parameters | B1 | B2 | B3 | B4 | B5 | B6 | GB |
---|---|---|---|---|---|---|---|
Perimeter (km) | 420.9 | 334.7 | 251.3 | 271.4 | 319 | 104.8 | 857.44 |
Mean Basin width (Wb) | 29.1 | 37.9 | 42.1 | 46.5 | 27.3 | 14.87 | 78.41 |
Basin Length (Lb) | 120.7 | 75.53 | 53.4 | 52.7 | 76.68 | 29.65 | 167.74 |
Number of streams (Nu) | |||||||
N1 | 478 | 420 | 330 | 359 | 267 | 32 | 1886 |
N2 | 101 | 90 | 67 | 58 | 57 | 12 | 385 |
N3 | 21 | 22 | 15 | 13 | 13 | 3 | 87 |
N4 | 5 | 4 | 2 | 5 | 3 | 1 | 20 |
N5 | 2 | 2 | 1 | 2 | 1 | 8 | |
N6 | 1 | 1 | - | 1 | - | - | 3 |
N7 | - | - | - | - | - | - | 1 |
Total | 608 | 539 | 415 | 438 | 341 | 48 | 2390 |
Total stream length (Lt) | |||||||
LT1 | 813.68 | 722.46 | 539.98 | 637.92 | 467.81 | 72 | 3253.84 |
LT2 | 451.76 | 363.97 | 260.92 | 215.39 | 271.88 | 38 | 1601.93 |
LT3 | 202.82 | 205.21 | 180.61 | 162.83 | 76.24 | 19 | 846.71 |
LT4 | 73.61 | 55.54 | 70.28 | 80.59 | 122.31 | 27 | 429.33 |
LT5 | 89.21 | 47.51 | 27.01 | 44.57 | 18.84 | - | 227.14 |
LT6 | 51.36 | 42.00 | - | 0.43 | - | - | 93.79 |
LT7 | - | - | - | - | - | - | 120. |
Total | 1682.44 | 1436.70 | 1078.80 | 1141.74 | 957.08 | 156 | 6572.75 |
Steam length Ratio (Lr) | |||||||
Lr1 | - | - | - | - | - | - | |
Lr2 | 2.63 | 2.35 | 2.38 | 2.09 | 2.72 | 1.41 | 2.41 |
Lr3 | 4.69 | 2.31 | 3.09 | 3.37 | 1.23 | 2.00 | 2.34 |
Lr4 | 0.70 | 1.49 | 2.92 | 1.29 | 6.95 | 4.26 | 2.21 |
Lr5 | 3.03 | 1.71 | 0.77 | 1.38 | 0.46 | - | 1.32 |
Lr6 | 1.15 | 1.77 | 0.02 | - | - | 1.1 | |
Lr7 | - | - | - | - | - | - | 3.84 |
Mean ratio | 2.44 | 1.93 | 2.29 | 1.63 | 2.8 | 2.56 | 2.20 |
Bifurcation ratio (Rb) | |||||||
Rb1 | - | - | - | - | - | - | |
Rb2 | 4.73 | 4.67 | 4.93 | 6.19 | 4.68 | 2.67 | 4.90 |
Rb3 | 4.81 | 4.09 | 4.47 | 4.46 | 4.38 | 4.00 | 4.43 |
Rb4 | 4.20 | 5.50 | 7.50 | 2.60 | 4.33 | 3.00 | 4.35 |
Rb5 | 2.50 | 2.00 | 2.00 | 2.50 | 3.00 | 2.50 | |
Rb6 | 2.00 | 2.00 | - | 2.00 | - | - | 2.67 |
Rb7 | - | - | - | - | - | - | 3.00 |
Mean Rb | 3.65 | 3.64 | 4.72 | 3.55 | 4.10 | 3.22 | 3.64 |
Parameters | B1 | B2 | B3 | B4 | B5 | B6 | Gilgit Basin |
---|---|---|---|---|---|---|---|
Area (km2) | 3510.14 | 2860.3 | 2247.4 | 2388.5 | 2091.4 | 440.6 | 13,538 |
Drainage density (Dd) | 0.48 | 0.50 | 0.48 | 0.4 | 0.46 | 0.35 | 0.50 |
Stream frequency (Fs) | 0.17 | 0.19 | 0.18 | 0.17 | 0.16 | 0.11 | 0.18 |
Form factor ratio (Ff ) | 0.24 | 0.50 | 0.79 | 0.84 | 0.36 | 0.50 | 0.481 |
Circulation ratio (Cr) | 0.25 | 0.32 | 0.44 | 0.41 | 0.26 | 0.50 | 0.231 |
Elongation ratio (Er) | 0.55 | 0.80 | 0.94 | 0.97 | 0.73 | 0.79 | 0.76 |
Length of overland flow (Lo) | 1.04 | 1 | 1.04 | 1.04 | 1.08 | 1.43 | 1.02 |
Drainage Texture (Dt) | 1.44 | 1.61 | 1.65 | 1.61 | 1.07 | 0.46 | 2.79 |
decrease with increase in stream order. The number of streams (Nu) in each order is presented in
According to Horton (1945), stream length refers to total length of stream segments in each consecutive orders. Stream length measures the average or mean length of a stream in each orders, and can be calculated by dividing the total length of all streams in an individual order by the number of streams in that order [
2.44, 1.93, 2.29, 1.63, 2.8 and 2.56 respectively. The results reveal that the Gilgit Basin and sub-basins bedrocks and surface materials are less permeable.
River networks have been analyzed in terms of the number of branches ordered according to a system proposed by Horton (1945) and modified by Strahler (1957). The ratio among the number of stream segments in one order and the next called the bifurcation ratio, and this quantitative ratio determines drainage network which exists in the form branches. It is a dimensionless property and shows the degree of integration prevailing between streams or various orders in a drainage basin. According to Horton (1945), the bifurcation ratio varies from a minimum of 2 in “flat or rolling drainage basins” and 3 or 4 in “mountainous or highly dissected drainage basins”. The bifurcation ratio range between 3.0 - 5.0 indicates substantial structural control on drainage basin. The mean Rb value of the Gilgit Basin is 3.64, while sub-basins Rb values ranges between 3.22 - 4.72, which falls within the stipulated range of natural drainage system as suggested by Horton and Strahler (1945, 1957). It was observed from the Rb values (
The drainage frequency introduced by Horton (1932 and 1945), which is directly connected to the lithological characteristics. The number of stream fragments per unit area is called stream frequency or drainage frequency. A high stream frequency characterized by high surface runoff, steeper surface, impermeable subsurface material, spare vegetation and high relief setting. The stream frequency of Gilgit Basin is 0.18 per km2 while Fs of 6 basin vary from 0.19 to 0.11. It was observed from the Fs values (
The main geometrical property of stream network is drainage density, which is the average length of channel per unit area of the basin. The poorly drained basin has a drainage density 2.74, while well drained has 0.73. Drainage density is ameasure of how frequently streams occur on the land surface. It reflects a balance between erosive forces and the resistance of the ground surface. It is closely related to climate, lithology, and vegetation. In drainage density analysis, inter-
mittent and ephemeral streams should be incorporated, because most of them performed during floods and bring flood water [
The form factor ratio is a dimensionless ratio of the basin area to the square of basin length. Form factor is the geometric index commonly used to characterize shapes of different basins. The value of form factor is in range, from 0.1 - 0.8 [
The circularity ratio is a dimensionless parameter which shows a quantitative index of the shape of the basin. According to Miller (1953), circulation ratio is the ratio of the area of the basins in the area of a circle having the same circumference as the perimeter of the basin. Circulatory ratio is influenced by the lithology of the basin, stream frequency and gradient of various orders [
The elongation ratio expresses the shape of the drainage basin, which is the ratio of the diameter of the circle of the same area as the basin to maximum basin length [
The elongation ratio of the Gilgit Basin is 0.76 while the sub-basins of values are range between 0.55 - 1, which is less elongated basin with high relief (
Hortonian overland flow happens when the rate at which rainfall surpasses the rate at which it can infiltrate into the soil. Their sustainability relies upon a supply of water from overland flow, through flow, interflow, base flow, and precipitation falling directly into the river. There are six independent variables which govern surface runoff phenomena such as rain intensity, infiltration capacity, length of overland flow, slope, surface roughness factor and type of overland flow Length. These factors are very important independent variables affecting both hydrologic and physiographic development of drainage basins [
<0.7 | Elongated |
---|---|
0.8 - 0.7 | Less elongated |
0.9 - 0.8 | Oval |
>0.9 | Circular |
erately high that indicates the basin encompasses of high relief, steep slope, young topography, snow melting (in summer) and rainfall enter into the stream very quickly. In streams up to 3rd order are surging through highly dissected and steep gradient mountainous terrain, which facilitates high overland flow and less water recharge into the subsurface and also ground water potential is low in these stream orders. The entire Gilgit river basin falls under mountainous terrain, most of the rainfall and snowmelt water is lost as surface runoff, without infiltrating into the subsurface, due to rapid overland flow on the steep gradient and impermeable lithology.
Drainage texture is one of the essential parameter in morphometric study, which shows spacing of drainage lines. Drainage lines are frequent and more active over impermeable areas than the permeable [
Strahler’s (1968) ruggedness number is the product of the basin relief and the drainage density and usefully combines slope steepness with its length. Raggedness number is used to measure the flash flood potential of the streams. Ruggedness number is the geometric characteristics of the basin and it is used to measure surface unevenness and also for assess the potential of flash flood in streams. Ruggedness number of Gilgit Basin is 3.83 and 6 sub-watersheds range 1.6 - 2.45. It was observed from the RN values (
The aspect refers to the direction a mountain faces; it pays a significant influence on its local climate, precipitation, snow melting, runoff generation, wind, vegetation, settlement and agriculture [
Relief aspects | B1 | B2 | B3 | B4 | B5 | B6 | GB |
---|---|---|---|---|---|---|---|
Ruggedness Number (RN) | 1.89 | 2.45 | 2 | 1.6 | 1.9 | 2.08 | 3.83 |
Relative Relief (ReRe) | 1.02 | 1.49 | 1.7 | 1.22 | 1.3 | 5.9 | 0.89 |
Relief Ratio (ReRa) | 0.036 | 0.07 | 0.08 | 0.06 | 0.05 | 0.21 | 3.85 |
Slope Degree (slopeD) | 2.06 | 3.79 | 4.60 | 3.68 | 3.10 | 11.79 | 2.21 |
Slope Ratio (SlopeR) | 3.59 | 6.62 | 8.05 | 6.42 | 5.42 | 20.87 | 3.86 |
basin.
Slope and elevation are two basic but distinct concepts in the study of landform. Slope is conceivably the most significant aspect of surface and surfaces are formed entirely of slopes. The slope may be defined as the perpendicular inclination between the hill top and valley bottom, stands with the straight line and expressed usually in degrees. The slope elements in any terrain controlled by climate and morphogenic processes operating in the underlying rocks [
Basin relief is the elevation difference of the highest and lowest point of the valley floor. The relief of Gilgit Basin is 6491 m. The sub-basins relief range from 3302 to 6187 m. North-west and south north of the basin shows comparatively high relief elevation. The relief ratio, (ReRa) is the ratio of maximum relief of horizontal distance along the longest dimension of the basin parallel to the principal drainage line. Relief ratio measures the overall steepness of a drainage basin and is an indicator of the intensity of erosion process operation on slope of the basin
[
The Relative relief (ReRe) or local relief represents a variation of altitude in a unit area with respect to the local base level. It is an essential morphometric variable used for the comprehensive assessment of morphological characteristics of the terrain. The ReRe map of the basin is present in (
Hypsometry is a scientific term means the relative proportion of an area at various elevations within a region and the hypsometric curve portrays the distribution of area with reference to altitude. Hypsometric analysis can be used to understand and evaluate various forcing factors acting on basin topography. Hypsometric analysis gives valuable information on landform development and various types of erosive processes operating on the landscape [
Name of Basins | Area (km2) | (HI) | Geologic stage |
---|---|---|---|
B1 (Gilgit-Gahkuch) | 3510.14 | 0.54 | Late youthful/inequilibrium |
B2 (Ishkoman) | 2860.3 | 0.46 | Mature/semi stabilized |
B3 (Yasin) | 2247.4 | 0.46 | Mature/semi stabilized |
B4 (Phunder) | 2388.5 | 0.53 | Late youthful/inequilibrium |
B5 (Gupis) | 2091.4 | 0.49 | Late youthful/inequilibrium |
B6 (Bagrot) | 440.6 | 0.40 | Mature/semi stabilized |
Gilgit Basin | 13538 | 0.50 | Late youthful/inequilibrium |
Morphometric analysis of drainage system is essential to any watershed related study. Gilgit river basin is located in the Hindu Kush and Karakoram mountains of Pakistan. Gilgit river basin is an important sub-basin of the upper Indus river basin. The study of Gilgit Basin morphometry successfully achieved by using ASTER DEM, Sentinel 2A image, coupled with geological and field data in the GIS environment. The entire basin is classified into six sub-basins, namely, Gilgit-Gahkuch (B1), Ishkoman (B2), Yasin (B3), Phunder (B4), Gupis (B5) and Bagrot (B6). The results of entire sub-basins shows dominated high relief, steep slope and youth to early mature fluvial geomorphic cycle. The first order streams are dominating in all the sub-basins, and drainage network with high number of lower order streams moving openly into higher orders.
Gilgit basin drainage density is 0.50 km/km2, which indicates that the basin area has well drained and impermeable surface material. The mean Rb value of the Gilgit Basin is 3.64, which falls within the stipulated range of natural drainage system as suggested by Strahler (1964). The values of stream frequency of the basin and sub-basins exhibit high impermeable geology, high relief and strong structural control on the drainage development. Gilgit Basin and sub-basins B2, B3, B4 are less elongated, while sub-basins B1, B5 and B6 reflect elongated shape. The ruggedness number is slightly higher for Gilgit Basin, which reveals high flash flood potential. The results of drainage texture indicate that the basin has coarse to very coarse texture. The hypsometry results indicate that the Gilgit Basin and sub-basins are in youthful stage towards the early mature stage.
Financial support for this research as part of the project “Sustainable Natural Resource Management for Climate Change Adaption” in the Himalayan region: A collaborative project among Norway, Nepal Pakistan and Bhutan. (Project No QZA-0485NPL13/0022), was provided by the NORHED program of NORAD.
Ali, K., Bajracharya, R.M., Sitaula, B.K., Raut, N. and Koirala, H.L. (2017) Morphometric Analysis of Gilgit River Basin in Mountainous Region of Gilgit-Baltistan Province, Northern Pakistan. Journal of Geoscience and Environment Protection, 5, 70-88. https://doi.org/10.4236/gep.2017.57008