Soil Erosion in Al-Adhaim River Basin, Central Part of Iraq

doi:10.21203/rs.3.rs-3235826/v1

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Soil Erosion in Al-Adhaim River Basin, Central Part of Iraq

https://doi.org/10.21203/rs.3.rs-3235826/v1

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Al-Adhaim River is a tributary of the Tigris River, it has three main tributaries: Khassa Soo, Aq Soo, and Tuz Chia, all of which are seasonal streams. The course of Al-Adhaim River and its three tributaries flow in a very rugged topography, especially in the upper courses with high gradients. The main present rocks in the catchment area are soft claystone with coarse conglomerate and sandstone, which are very easily eroded by running water, especially during floods. We have used SRTM images of ground resolution of 3-arc-second (90 m) and a vertical resolution of approximately 10 m to divide the catchment area into 14 sub-basins using ArcGIS (Arc map). Moreover, to calculate many factors concerning soil erosion, such as drainage density, erosion intensity, erosion rates, and soil erodibility. We have found that the drainage density ranges between (0.26–0.39) km/ km² with class Poor, the Erosion Intensity ranges between (264–387) m/km² with Very poor Zone, the Erosion rates (K_k) ranges from (0.01–0.325), and the Erosion Coefficient ranges from (0.7 − 1.0).

Erosion

erosion intensity

drainage density

soil erodibility

Al-Adhaim River

The catchment (Basin) area of Al-Adhaim Basin occupies the central part of Iraq (Fig. 1), with a coverage area of 12323.390 km². We have chosen Al-Adhaim River for our study because it is a very erodible river and was supplying the Tigris River with the maximum transformed loads as compared to the remaining tributaries [1]. Moreover, due to the diversity of the exposed rocks in the basin, the diversity of topography, and the basin extends in three different tectonic zones.

Al-Adhaim River consists of three main tributaries named: Khassa Soo, Tawooq (Aq or Daqooq) Soo, and Tuz Chai. The Tawooq Soo is the longest one and extends in the northern part of the catchment area within the High Folded Zone; there it is called Tinal Stream. Each of those three rivers has tens of large valleys: like Wadi Al-Kor, and Wadi Al-Karkha.

Figure 1: Location of the catchment area of Al-Adhaim River

The three rivers meet and run parallel to Himreen Range; there it is called Wadi Ezghytoon (Fig. 1). After crossing Himreen Range, it is called Al-Adhaim River (Fig. 1). The three rivers have 90 km, (0.1–1.1) km, 178 km, (0.1–1.4), and 138 km (0.1–1.0) km, as length and width, respectively. The total length of Al-Adhaim River is 330 km and merges with the Tigris River northwest of Baghdad by about 70 km. Floods take place from November to May each year, as they are mainly fed by rainfall. However, during the last 2 decades, flooding events are very rare due to drastic climate change.

Recently, Adhaim Dam is constructed in 20000, it is a multi-purpose embankment dam about 133 km northeast of Baghdad. The purpose of the dam is flood control, hydropower, and irrigation. The dam has decreased load supply to the Tigris River as well as decreased erosion capacity downstream of the dam.

1.1. Previous Work

Research concerning soil erosion in Iraq and particularly in Al-Adhaim River basin is very rare. The pioneering work of Buringh [1] is the most comprehensive performed work as soil type and erosion are concerned. According to Gibbs (1954) in Buringh [1], the Adhaim river was the main contributor of sediment. In 1938 the Tigris River carried 24 million m³, with 10 million m³ being carried during the peak flood. Abbas et al. [2] studied the climate change impact on the water resources of Al-Adhaim River. Khare et al. [3] studied the impact of climate change on soil erosion in India, we have adopted many parameters from their study. Sajadi et al. (2019) carried out a statistical analysis of the relation between tectonics and drainage behavior in India, we have adopted many parameters from their study. Hamdan et al. [5] studied the rainfall-runoff modeling in Al-Adhaim River basin to indicate the curve number. Hussain et al. [6] studied the modification of the spill way in Al-Adhaim Dam and presented a Land-Use and Land-Cover (LULC) map (Fig. 2a), and a spatial distribution of sediment sources (S S) map in the Adhaim watershed (Fig. 2b).

1.2. Aim

This study aims to indicate the drainage density, erosion intensity, erosion rates, and erosion coefficient in Al-Adhaim River basin. Besides, indicating galley erosion by total gulley lengths, sheet erosion per erosion intensity, soil erodibility, and soil types and erosion rates. Moreover, to prove that Al-Adhaim River basin exhibits severe erosion.

Figure 2. a) Land-use and land-cover map, b) Spatial distribution of sediment sources in the Adhaim watershed map (Both modified from [6].

The limits of the 14 sub-basins are imposed by the authors.

To indicate the required data and fulfill the aim of the current study, we have used satellite images of SRTM type with a ground resolution of 3-arc-second (90 m) and a vertical resolution of approximately 10 m. we also divided the catchment area of Al-Adhaim River into 14 sub-basins using ArcGIS (Arc map) (Fig. 3) to calculate the area of each sub-basin and the stream lengths, and to impose the 14 sub-basins on the Land Use – Land Cover map (Fig. 2a) and the sediments source map (Fig. 2b). Moreover, we have used different geological and topographical maps, and different published articles to calculate many factors concerning soil erosion, such as drainage density, erosion intensity, erosion rates, soil erodibility… etc.

We have calculated the drainage density according to the following equation:

Dd = Lu / Ba [7]

Where: Lu = Total stream length of all orders (km), and

Ba = Area of the basin (km²),

Figure 3: The catchment area of Al-Adhaim River is divided into 14 sub-basins.

The Erosion Intensity was calculated by the following equations:

AE=∑ L/A [8]

Where: AE = Erosion Intensity

L = Total length of the streams in the basin (m)

A = Total coverage area of the basin (km2)

We also have calculated erosion rate (K_k) and soil erodibility based on Khare et al. [3]. Based on Amiri (2010), we have calculated erosion coefficient (Ф), sheet erosion, and gulley erosion; both were classified into 6 classes; each based on Sajadi et al. [4].

Location

The study area is located in the central part of Iraq (Fig. 1) and covers about 12323.390 km². Al-Adhaim River flows almost in the central part of the study area, whereas the three main tributaries are well distributed in the area (Fig. 1).

Three main aspects of the geology of Al-Adhaim River catchment area are briefed hereinafter.

3.1. Geomorphology

The main geomorphological units and geodynamical processes are briefed hereinafter.

3.1.1. Geomorphological Units

- Units of Fluvial Origin

Terraces (Pleistocene): Usually two stages of terraces occur along the courses of the three tributaries. The main components are carbonates, quartz, and rare igneous and metamorphic rocks. The thickness is (1–5) m.

Alluvial Fans (Pleistocene): Three alluvial fans occur at the outlets of the three tributaries from the mountainous areas. The main components are sand, silt, and rare gravel

Alluvium

Alluvium sediments cover the western part of the Al-Adhaim basin. They are in form sheet run-off, flood plain and valley fill sediments

Valley In-fill Sediments

The tributaries of the river are filled by thick sediments. The pebbles are of carbonates, silicates, and rare igneous, and metamorphic rocks. The large valleys in the basin include clastic sediments; mainly gravel, sand, and silt. The thickness of these sediments varies between (< 1–5) m. The sediments are largely quarried for sand and gravel, in the three tributaries.

Flood Plain

The tributaries and the large valleys have wide flood plains along their courses. Locally, two stages are developed, with a height difference of (1–2.5) m. The sediments consist of sand, silt, and clay, with a few small pebbles.

- Units of Structural – Denudational Origin

Dissected Slopes

These are not well developed in the basin of Al-Adhaim River. They occur in areas built up by rocks of the Bai Hassan Formation. The dip slopes are densely dissected by valleys.

Anticlinal Ridges

They are well-developed in the rocks of the Injana and Mukdadiya formations. Due to the difference in hardness of the exposed rocks, long strike ridges and valleys occur, with the trellis drainage system.

Badlands

These occur widely in the basin of Al-Adhaim River, mainly in areas built up by the rocks of the Bai Hassan Formation (Fig. 4).

Figure 4: Typical Badlands east of Kirkuk city; within the rocks

of the Bai Hassan Formation

Hogbacks and Cuestas

These occur rarely in the studied basin within the Fatha Formation. The alternation of the folded rocks with different hardness has formed large successive flat irons in form of hogbacks and cuestas.

- Units of Denudational Origin

Pediments

These are present in different parts of the studied area, developed as continuous belts around the elevated areas, slopes, and ridges. Mainly consist of pebbles derived from the Bai Hassan Formation or of carbonate rock fragments, well cemented.

- Forms of Solution Origin

These units include sinkholes, which are developed in gypsum and limestone beds. The sinkholes are developed in different shapes and sizes; usually (1–8) m in aperture size and (1–5) m in depth. Some small caves are developed with different sizes.

3.1.2. Geodynamical Processes

Land Slides

These are formed along the cliffs of the Pila Spi Formation. The size of the slid masses reaches up to (0.1–1) cubic meters.

Toppling

This is well developed along the hard sandstone ridges of the Mukdadiya and Injana formations, and rarely along the Pila Spi Formation. The size of the blocks varies between (< 0.3– 2) m³.

Creep

This is very rarely developed along the slopes of the Bai Hassan, Gercus, and Kolosh formations. Usually step forms are developed, and the height of the steps ranges from (0.05–0.3) m.

3.1.3. Weathering and Erosion

These phenomena are very active in the Al-Adhaim River basin. Different types of both phenomena with different agents are developed, they are described hereinafter, briefly.

- Weathering: The clastic rocks are the most common rocks, which are exposed in Al-Adhaim River Basin; therefore, mechanical weathering is more active. The presence of Badlands (Fig. 4), which cover large parts of the basin is a good indication of mechanical weathering, besides the dense drainage system. However, chemical weathering is active only in the area built up by the rocks of the Pila Spi and Fatha formations. In the former, the carbonate beds are cavernous and karstified, whereas in the latter, different karst forms are developed in gypsum beds (Fig. 5), like sinkholes and caves.

- Erosion: The main erosion agent in Al-Adhaim River basin is the water. The three main types of erosion are Gulley, Rill, and Sheet. Gulley erosion is active in along the three tributaries of Al-Adhaim River and large valleys, where water gaps and gorges are developed. Rill erosion is developed on soft rocks, like claystone. Sheet erosion is well developed, especially in flat areas when is covered by a thin mantle of soil.

3.2. Stratigraphy

The exposed formations are presented in Fig. (5), and the geological map is presented in Fig. (6). The Quaternary sediments are described in more detail. All presented data are based on Sissakian and Al-Jibouri [9] and Sissakian and Fouad [10].

In Al-Adhaim River basin, the following Quaternary sediments of the Pleistocene and Holocene ages are developed, they are not presented in Fig. (5) due to scale limitations. They are products of weathering and erosion, the recorded thicknesses are a good indication of the active erosional processes in the basin.

Terraces (Pleistocene): These are developed along the courses of the Kassa Soo, Tawooq Soo and Tuz Chai, and Al-Adhaim River. The sediments consist mainly of gravel with sand layers. Usually, (2–3) levels are developed with thicknesses ranging from a few meters up to 7 m.

Figure 5. Generalized columnar section of the exposed formations

in Al-Adhaim River basin

Figure 6: Geological map of Al-Adhaim River Basin and surrounding areas

(Modified from Sissakian and Fouad [10])

Polygenetic Sediments (Pleistocene – Holocene): These sediments occur in the areas covered by the rocks of the Bai Hassan Formation, especially in topographically low areas. The main composition is pebbles with rock fragments of various sizes and types, mainly overlain by a thin veneer of gypseous soil. The thickness ranges from (1–10) m, and locally may reach 25 m.

Alluvial Fan Sediments (Pleistocene – Holocene): Rellics of alluvial fans are preserved in the northern parts in Al-Adhaim River basin. They are in form of plateaus and/ or mesas, covering Neogene rocks. The sediments consist of rock fragments and/ or pebbles consisting of different rocks in different shapes and sizes, and well-cemented. The alluvial fans are developed in areas where the three tributaries leave the hilly and mountainous parts of the basin. However, the alluvial fans almost vanished due to erosional and agricultural activities. The thickness of these sediments ranges from (3–8) m; locally may attain even more than 15 m.

Valley In-fill Sediments (Holocene): These sediments are well developed along the courses of the three tributaries of Al-Adhaim River. The sediments are composed of pebbles, which range in size from (1–25 cm) and rock fragments of carbonates, quartz, and a few igneous and metamorphic rocks. The thickness varies between (1–3) m, and may be more; up to 8 m.

Flood Plain Sediments (Holocene): These sediments are deposited along the three tributaries of Adhaim River. They are composed of sand, silt, and clay, with a few small pebbles. Their thicknesses range between (< 0.4–2) m, locally may be more, up to 6 m.

3.3. Tectonics and Structural Geology

Al-Adhaim River’s basin extends mainly within the Low Folded Zone. However, the northern and southern parts of the basin are within the High Folded and Mesopotamian zones, respectively. The three tectonic zones belong to the Unstable Shelf of the Arabian Plate [11]. According to Fouad [12]; however, the three zones belong to the Outer Platform of the Arabian Plate. Many folds are developed within the basin of Al-Adhaim River in the NW – SE trend. The NE limbs are locally thrusted over the SW limbs; accordingly, large parts of the anticlines are hindered below the thrusted part. Some synclines are unique in form of hanging synclines, like Khal Khalan and Taqaltu. The main anticlines in the basin are shown in Figure (6).

4.1. Drainage Density

Drainage density is defined as the ratio of the total length of channels of all orders in the basin to the drainage area of any basin [7]. The Drainage density as an index of the closeness of spaces in a channel [7] is affected by many factors; climate, lithology, vegetation, and geological conditions of the area [13]. The characteristics of stream length are controlled by resistance to weathering, climate, vegetation, the permeability of the rock, etc. It is an indicator of the nearness of channel spacing which provides measurable data about the average stream channel length for the whole basin [14]. It can be calculated according to equation No. (1):

Dd = Lu / Ba [7] ……………………………… (1)

Where: Lu = Total stream length of all orders (km), and

Ba = Area of the basin (km²)

According to Deju (1971) in Kinthada et al. [15], the drainage density is divided into three types depending on the Dd values: Poor (0.5), Medium (0.5–1.5), and Excellent (1.5). Whereas Sajadi et al. [4] considered that High drainage density refers to a basin with high relief accompanied by hard rocks, whereas low drainage density points to the reverse case indicating a basin with low relief and low surface topography. Reviewing the acquired data in Table (1); as the drainage density is concerned, we can see that all 14 sub-basins showed Poor drainage density since the values range from (0.26–0.39).

4.2. Erosion Intensity

Erosion intensity represents the ratio between the total length of a basin to its total area, it can be calculated by equation No. (2).

AE=∑ L/A [8] …………………………. (2)

Where: AE = Erosion Intensity (Average Erosion)

L = Total length of the streams in the basin (m)

A = Total coverage area of the basin (km²), and

Following the classification of Bergsma [8] for the erosion intensity given in Table (2) and considering the acquired values of erosion intensity presented in Table (1), all sub-basins show Very Low erosion intensity.

Table 1: Different calculated data at the 14 sub-basins of Al-Adhaim River Basin

Sub-basin No.		Area (km²)	Stream Length (m)		Drainage Density			Erosion Intensity			Tectonic Zone		Main Lithology [9]
					Value (km/km²)		Class [15]	Value (m/ km²)		Zone [8]
1		1551.826	498860.687		0.32		Poor	321		Very Low	Mesopotamia
2		419.619	127462.205		0.30			304			Low Folded
3		347.786	526050.420		0.31			307			High Folded
		1368.579									Low Folded
4		831.656	299551.114		0.36			361
5		57.663	578669.670		0.32			316			High Folded
		1776.464									Low Folded
6		728.137	269970.426		0.26			264			High Folded
		296.284									Low Folded
7		723.192	274290.148		0.38			379
8		324.819	100841.618		0.31			310
9		796.738	296754.646		0.37			372
10		953.566	311889.374		0.33			327
11		411.505	152367.592		0.37			370
12		119.954	43010.444		0.36			359
13		146.894	56834.594		0.39			387
14		1468.707	493228.607		0.34			336
	Alluvium			Claystone		Sandstone			Conglomerate			Gypsum		Limestone

Table 2: Classification of Erosion Intensity (After [8])

Table 2

Classification of Erosion Intensity (After [8])
Class	Erosion Intensity (m/km²)	Erosion Zone
1	1–400	Very Low
2	401–1000	Low
3	1001–1500	Moderate
4	1501–2700	High
5	2701–3700	Very High
6	3701–4700	Extremely High
7	> 4700	Very Extremely High

From reviewing the topographic and geological maps, besides satellite image interpretations, all 14 sub-basins exhibit Gulley erosion. Considering the Gulley erosion classification given by Sajadi et al. [4] (Table 3) and comparing them with the estimated values of the erosion intensity (Table 1), then all 14 sub-basins show Slight erosion intensity because the erosion intensity ranges between (264–387) m/ km² (Tables 1 and 3).

Table 3

Classification of the gulley erosion by total gulley length (After Sajadi et al. [4])
Grade	Erosion intensity		Verbal Assessment	Sub-basin No.
Grade	(km/ km²)	m/ km²	Verbal Assessment	Sub-basin No.
1	< 0.10	< 100	No erosion or insignificant erosion
2	0.10–0.50	100–500	Slight erosion	1–14
3	0.5–1.0	500–1000	Moderate erosion
4	1.0–2.0	1000–2000	Severe erosion
5	2.0–3.0	2000–3000	Very severe erosion
6	> 3.0	> 3000	Catastrophic erosion

Table 3: Classification of the gulley erosion by total gulley length

(After Sajadi et al. [4])

The Sheet erosion is active only in sub-basins Nos. 1, 12, and 14, in other sub-basins is less active; as deduced from the topographical maps of 1:100000 on the scale and geological maps of the same scale, besides interpretations of satellite images. We have considered the classification of Sajadi et al. [4] for sheet erosion, which depends on the erosion intensity (Table 4). We have used the data of Hussain et al. [6] (Fig. 2b) and converted the used unit (ton/ ha) to m³/ ha, by dividing the weight by the density of the soil, considering the average soil density is 1400 kg/ m³.

Table 4

Classification of the sheet erosion per erosion intensity (After [4])
Grade	Erosion intensity (m³/ ha/year)	Verbal Assessment
1	< 0.5	No erosion or insignificant erosion
2	0.5–5.0	Slight erosion
3	5.0–15.0	Moderate erosion
4	15.0–50.0	Severe erosion
5	50.0–200.0	Very severe erosion
6	> 200.0	Catastrophic erosion

Table 4: Classification of the sheet erosion per erosion intensity (After [4])

The used units by Hussain et al. [6] start from (0.00030–0.00059) ton/ha to (0.39–0.4) ton/ ha (Fig. 2b), we have converted them to m³/ha units, then the units will be (0.00021–0.00042) m³/ha. Accordingly, when we compare the units with the classification of Sajadi et al. [4] (Table 4), then the result will be Insignificant Erosion Intensity.

We also have adopted the classification of Khare et al. [3] about the soil erodibility factor (Kk) and applied its details to the 14 sub-basins using the geological map (Fig. 6) and other geological data. Accordingly, different soil erodibility factors were indicated in the 14 sub-basins (Table 5). Consequently, different erosion rates were indicated for the 14 sub-basins (Table 5).

Table 5

Soil erodibility factor at the 14 sub-basins (The factor values and definitions are from Khare et al. [3])
No.	Soil type	Erosion rate	K k	Sub-basins No.
1	Moderately – deep/soil of side slopes/ fluvial	Slight erosion	0.01	1, 8, 11, 12 and 14
2	Moderately shallow/ soil of side slopes	Moderate erosion	0.15	2, 4, 10 and 13
3	Shallow/soil of side slopes	Severe erosion	0.25	5 and 7
4	Very shallow/soil of side slopes	Very severe erosion	0.325	9
5	Soil at cliffs	Very very severe erosion	0.40	3 and 6

Table 5: Soil erodibility factor at the 14 sub-basins

(The factor values and definitions are from Khare et al. [3])

We have adopted the classification of Amiri [16] for indicating the erosion coefficient depending on the slope, type of soil and/ or rock, and drainage density of the 14 sub-basins. To indicate the slope and soil and/ or rock type, we have used topographical and geological maps at a scale of 1:100000.

Based on the soil types at the 14 sub-basins, different erosion rates were indicated (Table 7) by using the classification introduced by Khare et al. [3]. The results showed that the erosion rates differ from Slight to the Veryverysevere rate of erosion. These erosion rates in the 14 sub-basins match better than any other previously presented erosion rates and/ or intensities.

Table 6: Erosion coefficient in the 14 sub-basins (Adopted from Amiri [16])

Table 6

Erosion coefficient in the 14 sub-basins (Adopted from Amiri [16])
No.	Explanation of erosion properties in facies or sampling units	(Ф)	Sub-basin No.
1	The area that immensely covered by a head cat or gully erosion	1.0	3, 5 and 6
2	The area that covered 80% by gully erosion or rill erosion	0.9	4, 7 and 10
3	50% of the area is covered by gully erosion or rill erosion	0.8	2, 9 and 13
4	The area that is immensely covered by surface erosion, mass movement, and with less Karst, gully erosion, and rill erosion	0.7	1, 8, 11, 12 and 14
Note: The remaining Erosion Coefficients (Ф) values from 0.6 to 0.1 do not match with the soil types at any of the studied 14 sub-basins.

We considered soil and erosion types in this discussion. We didn’t consider the climate factors, especially annual rainfall as erosion is concerned, because the basin area is under the same climate conditions, although the sub-basin No. 6 receives yearly slightly more rainfall.

Table 7: Soil types (after Khare et al. [3]) and erosion rates at the 14 sub-basins

Table 7

Soil types (after Khare et al. [3]) and erosion rates at the 14 sub-basins
Sub-basin No.	Soil type	Erosion rate	K k	Sub-basin No.	Soil Type	Erosion rate	K k
1	1	Slight	0.01	8	1	Slight	0.01
2	2	Moderate	0.15	9	3	Severe	0.25
3	4	Very severe	0.325	10	3
4	4	Very severe	0.325	11	3
5	5	Very very severe	0.40	12	1	Slight	0.01
6	5	Very very severe	0.40	13	4	Very severe	0.325
7	3	Severe	0.25	14	2	Moderate	0.15

We have studied different erosional aspects and compared them with the LULC and SS maps, besides the type of exposed rocks and/or sediments at each sub-basin. To facilitate the discussion, we have arranged a special table (Table 8) in which we presented the main discussed aspects.

Table 8

Main rock and/ or sediment types and the values of the 7 erosion aspects
Sub-basin No.		Soil type [3]	Drainage Density (km/km2)		Erosion Coefficient (Φ)	Soil Erodibility Factor (K_k)		Erosion Rate [3]	Erosion Intensity [8]		Gulley Erosion [4]	Sheet Erosion [4]
1		1	0.32		0.7	0.01		Sl	Very slight		Slight	Insignificant
2		2	0.30		0.8	0.15		M
3		4	0.31		1.0	0.4		VS
4		4	0.36		0.9	0.15		VS
5		5	0.32		1.0	0.25		VVS
6		5	0.26		1.0	0.4		VVS
7		3	0.38		0.9	0.25		S
8		1	0.31		0.7	0.01		Sl
9		3	0.37		0.8	0.33		S
10		3	0.33		0.9	0.15		S
11		3	0.37		0.7	0.01		S
12		1	0.36		0.7	0,01		Sl
13		4	0.39		0.8	0.15		VS
14		2	0.34		0.7	0.01		M
	Alluvium			Claystone			Sandstone			Conglomerate			Gypsum	Limestone
Sl = Slight, M = Medium, S = Severe, VS = Very Sever, VVS = Very very severe
For Soil types [3] refer to Table (5).

Table 8: Main rock and/ or sediment types and the values of the 7 erosion aspects

Sl = Slight, M = Medium, S = Severe, VS = Very Sever, VVS = Very very severe

For Soil types [3] refer to Table (5).

The achieved data about Erosion Intensity [8], Gulley, and Sheet erosion [4] showed Very slight, Slight, and Insignificant values, respectively (Table 8). When comparing the rocks and soil types, and the topography, most of the sub-basin (apart from sub-basins No. 3, 5, and 6) bear the same rock types and soil (Table 8). However, they showed the same erosion intensity, gulley, and sheet erosion values. This means that the existing rocks and soil types do not affect erosion, which is not acceptable. Moreover, the drainage density of all basins according to Deju (1971) in [15] showed Poor class, which is again not acceptable. These discrepancies of the mentioned values at the 14 sub-basins can be attributed to 1) No detailed data exists about soil types at each sub-basin, 2) The accuracy of the used data to indicate the values of the three erosion aspects, and 3) the Accuracy of the used DEM by means of which the coverage area and streams’ length at each of 14 sub-basins were determined. Therefore, we will consider only the erosion rates (Table 8).

The acquired erosion rates, however, showed quite different estimates; according to Kkare et al. [3] for the different 14 sub-basins. We have compared the acquired estimates with the type of the exposed rocks and present soil types at each sub-basin and the LULC, and SS maps (Fig. 2), we have found excellent coincidence, not only in the estimated values but even the limits of the sub-basins which coincide with the SS map (Fig. 2b). The rate of the supplied sediments (SS map, Fig. 2b), when compared with the LULC map (Fig. 2a), is low in sub-basins No. 8, 11, 12, and 14, and partly in sub-basin 9. This is attributed to the type of LULC which is agricultural (cultivated) lands; therefore, the erosion rate will be low and accordingly, the sediments’ supply will be low too. Moreover, the erosion rate ranges from Very Slight to Sever (Table 8). In the sub-basins No. 3, 4, 5, 6, 7, and 10 the erosion rates range from Very Sever to Very very Severe (Table 8). In the SS map (Fig. 2b) the sediments supply map also shows the high range of sediments supply and the LULC map (Fig. 2a) shows Pasture, which is arable lands and due to grazing then the erosion will be high. In sub-basins No. 2, 9, and 13, the erosion rates range from Medium to Very Severe (Table 8), therefore, the SS map (Fig. 2b) shows moderate sediment supply and the LULC map (Fig. 2a) shows partly Pasture and partly Agricultural lands. The effect of the exposed rocks (Table 8) is clear in sub-basins No. 3, 5, and 6 (all types of rocks are exposed) and because there are anticlines with high dip amounts; therefore, the erosion rates will be Vey Sever to Ver very Sever, besides the sediments supply will be high (Fig. 2b).

The main conclusion about the soil types and erosion is that there is excellent relation between Erosion Rates and the 1) types of exposed rocks, 2) present soil types, 3) LULC cover map, and 4) SS map. However, other calculated and/ or estimated values of drainage density, erosion coefficient (Φ), soil erodibility (K_k), erosion intensity, gulley erosion, and sheet erosion showed faint relation with the mentioned 4 aspects. Moreover, the erosion rates in the 14 sub-basins range from Slight Erosion to Very Very severe Erosion, the Severe and Very Very Severe Erosion being dominant in 9 sub-basins (Nos. 3, 4, 5, 6, 7, 9, 10, 11, 13 and 14). Whereas the Soil Erodibility factor ranges from 0.01–0.4, which means Slight to Very Very Severe Erosion, especially in sub-basins No. 3, 5, 6, 7, and 9, covering an area of 5371.651 km², which means 43.59% from the total area of the basin suffer from Severe to Very Very Severe Erosion.

Acknowledgment

The authors express their sincere thanks to the authorities of the Komar University of Science and Technology and the University of Salahideen for providing the logistics during the fieldwork.

Author contribution statement:

V.K. Sissakian and Z.Elyias: Analyzed and interpreted the data, contributed reagents, materials, analysis tools, or data, and wrote the paper. N. Al-Ansari contributed to the discussion and amending the article.

Funding statement:

All authors declare that there was no fund and no financial benefit during the performance of the current work.

Data availability statement:

All the data used during this study appear in the submitted article, other related data will be available from the first author upon reasonable request.

Declaration of interest’s statement:

All authors declare that there was no conflict of interest; as the current work is concerned.

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No competing interests reported.

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Soil Erosion in Al-Adhaim River Basin, Central Part of Iraq

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Abstract

Figures

1. Introduction

1.1. Previous Work

1.2. Aim

2. Data Used and Methodology

3. Geological Setting

3.1. Geomorphology

3.1.1. Geomorphological Units

3.1.2. Geodynamical Processes

3.1.3. Weathering and Erosion

3.2. Stratigraphy

3.3. Tectonics and Structural Geology

4. Results

4.1. Drainage Density

4.2. Erosion Intensity

5. Discussion

6. Conclusions

Declarations

References

Additional Declarations

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