The Al-Abiadh Valley Drainage Basin Environmental Aspects Extraction Using Quantitatively Morphometric Analyses of Shuttle Radar Topographic Mission Data

The accurate extracting, studying, and analyzing of drainage basin morphometric aspects is important for the accurate determination of environmental factors that formed them, such as climate, tectonic activity, region lithology, and land covering vegetation. This work was divided into three stages; the 1 st stage was delineation of the Al-Abiadh basin borders using a new approach that depends on three-dimensional modeling of the studied region and a drainage network pattern extraction using (Shuttle Radar Topographic Mission) data, the 2 nd was the classification of the AlAbiadh basin streams according to their shape and widenings, and the 3 rd was extracting then taking up the quantitative analysis technique to estimate the basin morphometric aspects and the basin's environmental parameters that created them. The Al-Abiadh valley basin is a six-order one with a dendritic, parallel, and deranged drainage network. The flood hazard is absent at the basin mouth because the valley runoff takes a long time to reach the sink (Al-Razaza Lake), located in the middle part of Iraq, with a low flow peak due to the high permeability soil, the arid to semi-arid climate, and the low annual precipitation rate. The region studied is an alluvial basin with similar geological structural solidity in most places. The drainage network was found to be controlled by lineaments and fracture traces; the basin has passed its youth geomorphic phase.


Introduction:
The existence of water resources is the principal underpinning that civilized society builds on.Every ancient civilization, Sumerian, Egyptian, and Indus arose from great river basins (1).From this perspective, the extraction of a basin's hydrological aspects (in terms of geometrical morphometric parameter delineation) is essential for good planning and control of irrigation projects especially in arid or arid-threatened regions.Recently Iraq has suffered from increment evapotranspiration rates due to rising average temperatures (2,3).
The key factor for this rise is the effect of global warming.In Iraq, the ratio of arid land area was 88% of its total area in the first decade of this millennium compared to 72% in the seventies.(4) 1 Remote Sensing Unit, College of Science, University of Baghdad, Baghdad, Iraq. 2 Remote Sensing and GIS Department, College of Science, University of Baghdad, Baghdad, Iraq.* Corresponding author: Laithalsaadi@scbaghdad.edu.iq The application of the quantitative morphometric approach that was submitted by Horton and improved by many scientists, notably Strahler, is proven to accurately delineate not only the basin hydrological aspects, but also the lithological, geomorphological, and climatic aspects (5).The utilization of GIS techniques to implement quantitative analyses on remotely sensed data rather than classical techniques that depend on a topographical map is important to certify measurement accuracy (6).

The Study Area:
The Al-Abiadh valley drainage basin is one of Iraq's western plateau endorheic basins that drains into the Al-Razaza sink.The extent of the basin spans from 40º 32' 42''.304 to 43º 46' 15''.134 east longitude and from 31º 27' 29''.222 to 32º 39' 15''.134north latitude which covers 18608.924square kilometers.90.72% of the basin area falls in the Al-Anbar province, 4.76% in Karbala province, Open Access 0.85% in Al-Najaf, and 3.6% of the basin area is located in Saudi Arabia (a cross borderline basin).
The region's climate is arid to semi-arid with rare seasonal rainfall that does not exceed (120 mm); the annual mean of the minimum/maximum temperatures are (24Cº) and (36Cº) respectively.The basin's inhabitants are the wandering nomads that travel along the Al-Abiadh valley rivulets to graze their livestock on desert plants such as wormwood (7). Figure (1) illustrates this region.

Materials and Methods:
For this article the work was divided into three stages: A. The basin's watershed delineation and drainage pattern extraction from 90m using Shuttle Radar Topographic Mission (SRTM) Digital Elevation Model (DEM).B. The classification of basin streams according to their pattern shape and according to their channels' width and gradient.
C. The determination of basin morphometric aspects using empirical mathematical equations and/or Arc GIS facilities, then taking a quantitative analysis approach to estimate the basin's geological, lithological, geomorphological, and climate characteristics using morphometric parameter values.
The first stage was achieved by following the classical steps illustrated in fig.
(2) below: The semi-flat terrain of the basin and its surroundings make the watershed determination difficult, so in this work a new approach was submitted, which is the use of three-dimensional modelling of the region with a double increment in the terrain's height than its real one.Using this technique was sufficient to isolate the basin's border (watershed) from its neighborhoods as in fig.
(3) The second stage involves two approaches as follows: Visual classification of the streams according to their pattern shape.This is a subjective process that requires an expert interpretation, as the Al-Abiadh valley drainage basin's network pattern system can be distributed among three classes as shown in fig.(4).Visual classification of the streams according to their channels' width and gradient.To achieve this (the interpolate line tool and the create profile graph tool), which are 3D analyst tools of Arc GIS, were utilized.For the Al-Abiadh valley drainage basin the stream's width increases as the order increases, while the stream channel gradient decreases with the increment of the stream order, with one exception, the 6 th order stream which represents the basin valley stream, and the gradient of this valley is very high referring to primary geomorphic stage of this valley.These situations are shown in fig.The third stage consists of determining and analyzing the following aspects:

Linear aspects:
The ordering process of the basin's streams is the first step of hydro-morphometric analysis because the water and sediments of the cachement area are moving through the drainage system to a single stream, which is considered the basin order (i.e. the highest order stream in the basin) (8).By using Arc GIS measurements, the basin's real length was 310.2km and the ideal length was 380.475km.The basin's width was 55.941km, while the perimeter was 950.816km.

1.Stream Order (U):
Five distinct schemes of stream ordering was submitted; the 1 st scheme was introduced by Gravelius, the 2 nd was Horton's scheme, the 3 rd was Strahler's, the 4 th was Shreve's, and the 5 th scheme was Schideggar (9).The method utilized in this paper was Strahler's, which is considered a slight modification of Horton's ordering process.
The Al-Abiadh basin drainage pattern was automatically modelled by utilizing ArcGIS 9.3 hydrology Arc tools for modelling software and 90m SRTM as ancillary data.The Al-Abiadh valley basin was found to be a six-order basin.

2.Stream Number (Nu):
The Al-Abiadh basin has (672 1 st order streams, 321 2 nd order streams, 213 3 rd order streams, 59 4 th order streams, 28 5 th order streams, and 44 6 th order streams).The streams of each order can be seen in fig.(6) Figure 6.The Al-Abiadh valley drainage basin streams for each of its orders.

Bifurcation Ratio (Rb):
The mean value of all Rbs of the basin is a considerable measurement because of its impact on the discharge rate (i.e. a higher Rb value means lower flood hazard in the discharge area and vice versa) (9).The average was 1.9906, which means that a flood hazard is absentthis is because the soil of the study area is sandy (high permeability), resulting in a low runoff yield.The 5 th Bifurcation Ratio refers to a high discharge rate in the valley (the 6 th order streams).

Drainage density (Dd):
Drainage density is a topographic aspect with principal importance, since it is a parameter with high sensitivity that links the basin's attribute configuration and the processes working on the stream channel shape.It is a reflection of the landuse which influences the infiltration and response time between rainfall and discharge (10).Dd value can be classified into three categories as follow in table 1.The Al-Abiadh valley basin's Dd is low (0.325km/km²), which in general refers to highly permeable soil and an arid to semi-arid climate with a low precipitation value.

Stream (Drainage) frequency (Fs):
Fs is directly related to the lithological properties of the region, structure hills often have high Fs values, while alluvial fan basins usually have lower Fs (11).For every basin there is a direct correlation between Dd and Fs values (12).The Al-Abiadh valley basin's Fs is 0.071 stream/km² highlighting that the region is an alluvial basin.

Drainage Texture (Rt):
Rt has an essential importance because the capacity of infiltration and lithology of underlying layers has a major dependence on it.Rt is influenced by vegetated cover density, the permeable quantity of soil, relief, and climate (5).There are five various textures (very coarse <2, coarse 2-4, moderate 4-6, fine 6-8, and very fine >8) (10).The Al-Abiadh valley basin's Rt was 0.706 stream/km, indicating that the drain texture was very coarse and basin permeability was very high, due to variants of the drainage texture along the study area.

Elongation ratio (Re):
The Al-Abiadh valley basin's Re is 0.496 (i.e. the basin shape is median elongated and the geological structures' solidity is the same throughout the basin).

Circularity ratio (Rc):
The Al-Abiadh valley's basin Rc is 0.258 (i.e. it is far from a circular shape and its drainage pattern is controlled by the lineaments and fracture traces.In addition, the watershed's lines are irregular and the basin is generally in the youth phase of the geomorphic cycle).

Form factor (Rf):
The Al-Abiadh valley's basin Rf is 0.193 (i.e. it has an elongated shape with a low peak flow, long duration, and absent of a flood risk).
Relief Aspect:

Basin Relief (H):
The Al-Abiadh valley's basin relief is (677m).It is generally a highly valued relief valley.

Relief ratio (Rh):
The Al-Abiadh valley's Rh is 0.458 (i.e. the basin is in the primary stage of maturing, since a low value Rh means lower erosion power and sediment yield towards the basin's mouth).

The Constant of Channel Maintenance (C):
C of the study area is 3.076km (i.e.The Al-Abiadh basin is an alluvial basin with strong lithology control).

Conclusions:
The use of the quantitative morphometric analysis is essential not only to determine the environmental factors that created any basin, but to also find the best ways to invest in it.The Al-Abiadh valley drainage basin was found to be a sixorder basin.The mean value of the Bifurcation Ratio was (1.9906), reflecting the absence of a flood hazard at the basin mouth, and the high permeability soil in it.
The value of the drainage density was 0.325 km/km², indicative of an arid and/or semi-arid climate with a low annual precipitation rate.The stream frequency value is 0.071 stream/km² indicating that the study region is an alluvial fan basin.The basin's geological structure solidity was found to be the same all over the basin since elongation ratio value was 0.496.The basin's drainage network is controlled by the lineaments and fracture traces as circularity ratio is 0.258.
The valley runoff water takes a long time to reach the sink (Al-Razaza Lake) with a low flow peak because form factor value is 0.193.Relief ratio was 0.458 indicating that erosion power is low and the sediment yield quantity towards the basin's outlet is low.This low R f value and the steepness of the sixth order stream (basin stream) indicates the primary stage of the geomorphic cycle for the Al-Abiadh valley.

Figure 1 .
Figure 1.Iraqi administrative map illustrating the Al-Abiadh valley basin's drainage network.

Figure 2 .
Figure 2. The block diagram that demanded traditional steps to define a basin's watershed and drainage network.

Figure 3 .
Figure 3.The three-dimensional modelling of the region with an illustration of the extracted basin area.

Figure 4 .
Figure 4.The Al-Abiadh valley's drainage basin network pattern system classes.

( 5 )Figure 5 .
Figure 5.The Al-Abiadh valley drainage basin streams' order profile graph; a) 1 st stream's order profile b) 2 nd stream's order profile c)3 rd stream's order profile d) 4 th stream's order profile e) 5 th stream's order profile f) 6 th stream's order profile