Estimation of Soil Erosion in the Drainage Basin of Cakmak Dam

*Murat Pınarlık and Zeliha Selek* 

#### **Abstract**

 Soil erosions have negative impacts on the economic life and sustainable operations on dams which are built in basins due to the filling of reservoirs. The sediment carried by stream erosion causes the dead and active capacity of the dam reservoir to be filled and the socioeconomic benefits to run out. Therefore, it has great importance to calculate the soil losses for the sustainable management of soil and water resources in the drainage basins of dams. Soil losses resulting from erosion can be calculated with the help of various equations and methods given in the literature. One of these methods is revised universal soil loss equation (RUSLE) model. In this study, soil losses resulting from erosion, which is located in the drainage basin of Cakmak dam in Yesilirmak basin, was calculated with RUSLE model, and the effect of erosion on the reservoir capacity was revealed by a geographic information system (GIS). According to the results, slightly above 90% of low to very low erosion and 5% of high to very high erosion were determined in the drainage basin of Cakmak dam.

**Keywords:** erosion, RUSLE equation model, GIS, Cakmak dam, sustainable dam

#### **1. Introduction**

 Although soil erosion is a natural part of erosion, it threatens the sustainability of natural resources [1]. Soil erosion is an important environmental problem that reduces soil productivity and water quality, causes sedimentation, and increases the probability of floods worldwide [2]. Important terrain features influencing the mechanism of soil erosion are slope, length, aspect, and shape. Particularly, the impact of slope and aspect plays a major role in runoff mechanism. The greater the gradient the slope has, the more runoff occurs, and hence, the infiltration reduces. The increase of the flow velocity depending on the slope will cause the erosion of soil [3]. Recently, soil erosion which is an important problem in the whole world also damages the lands of Turkey greatly. In our country, 54% of forest areas, 59% of agricultural areas, and 64% of pastures are under the influence of moderate and high erosion [4]. Defective topography and climatic conditions of Turkey create a favorable environment for erosion. However, besides physical factors, human impacts are considerably high [5]. Soil erosion is a result of the interaction between soil erodibility and rainfall erosivity factors. Failure of human practices such as planting, desertification, an extension of urban areas and roads, unregulated, and overgrazing also accelerate this problem [6, 7].

Water erosion is the main type of physical land deformation in the global perspective [8]. Besides, due to the loss of fertile soil in agricultural areas, it is risky for food safety and represents a serious barrier to sustainable development [9]. Water erosion causes soil particles to be removed through raindrops. Flow on the surface also carries out the transport process [10]. Sediment formation in mountain basins starts with landslides on steep slopes. The risks associated with this are the deposition of sediment in the reservoirs and the transportation of the sediment to the water networks [11]. All parts of catchments are closely linked together by the behavior of streams, land use, and any disturbance in the hydrological and biotic environments. Therefore, river catchments are dynamic and vulnerable systems. Especially when exposed to human impacts, it can change significantly, because, the system should be adjusted to remove this unnatural disturbance again [12]. The total land area, which is subjected to human-induced soil degradation, is estimated about 2 billion hectares. Furthermore, the land area affected by soil degradation due to erosion is estimated at 1100 Mha by water erosion and 550 Mha by wind erosion [13].

 Particularly predictive models are needed to reduce corrosive processes in soil use and management of basins. Models developed to calculate soil erosion can be divided into empirical and conceptual and based on physical processes of soil erosion [14, 15]. Empirical models are fast in predicting erosion, but for a specific area, long-term data collection is required [16]. Also, empirical models are widely used for measurement of the surface soil loss and sediment yield from the catchment areas [17]. Physical-based or process-based models are based on mathematical equations that define the erosion process. These models are designed to represent the necessary mechanisms to control erosion. The advantage of physical-based models is the synthesis of a single component associated with various factors. Furthermore, they represent erosion involving complex interactions between their spatial and temporal changes [18]. In the studies related to the determination of soil erosion, physical-based methods are generally used such as USLE, RUSLE, CORINE, and LEAM [19–21]. The most widely used of these methods is revised universal soil loss equation (RUSLE) [22–24]. In addition to RUSLE method, GIS, STATSGO, SSURGO, and remote sensing systems have been used and benefited their soil databases [25–31]. The results obtained were found to be highly effective and usable compared to other methods.

In this study, the soil losses resulting from erosion, which is located in the drainage basin of Cakmak dam in Yesilirmak basin, were calculated with RUSLE model, and the effect of erosion on the reservoir capacity was revealed by geographic information system (GIS).

#### **2. Study area**

 In this research, Cakmak dam drainage area, which is located in Yesilirmak subbasin of Yesilirmak basin in Turkey, was discussed. Yesilirmak basin is the third largest basin in Turkey with the surface area of 38,387 km2 . Yesilirmak subbasin covers approximately 32% of this area (11,961 km2 ). When the land use of the Yesilirmak subbasin is examined, it includes the irrigated agricultural area 12.18%, the dry agricultural area 12.89%, the mountain pasture 9.43%, the forest 37.46%, and the steep slopes without trees 28.04%. Cakmak dam drainage area is 47,862.7 ha. The lake surface of Cakmak dam was calculated as 500 ha by geographical information system (GIS). The following calculations were obtained by subtracting the dam lake surface from the drainage area. The maps showing the location of the Cakmak dam drainage area on the basin are given in **Figure 1**.

**Figure 1.**  *Location of the drainage basin of Cakmak dam in Yesilirmak basin.* 

#### **3. Materials and methods**

 The map of soil loss to Turkey's river's reaching was revealed by revised universal soil loss equation (RUSLE). The dynamic erosion model and monitoring system (DEMMS) has formed the dynamic structure of this model. It has been developed to provide monitoring and reporting between years. With this system, the effects of changes in soil-water conservation activities in the kinetic energy of the rain with changes in land cover can be monitored temporally, spatially, and areally [32].

 Soil losses caused by erosion with various methods and equations are calculated. The most prevalently used of these methods is revised universal soil loss equation (RUSLE). Soil losses which are transported and as a result of erosion in the drainage area of Cakmak dam in Yesilirmak basin were calculated by RUSLE equation. The revised RUSLE is denominated as follows [33, 34]

$$A = R\*K\*L\*S\*C\*P\tag{1}$$

where A is the annual soil loss (t ha<sup>−</sup><sup>1</sup> y<sup>−</sup><sup>1</sup> ), R is the rainfall erosivity factor (MJ mm ha<sup>−</sup><sup>1</sup> hour<sup>−</sup><sup>1</sup> y<sup>−</sup><sup>1</sup> ), K is the soil erodibility factor (t ha hour ha<sup>−</sup><sup>1</sup> MJ<sup>−</sup>1 mm−<sup>1</sup> ), L is the length of slope, S is the slope steepness, C is the cover management factor, and P is the erosion control practice factor.

In this study, the data sets provided by the General Directorate of Combating Desertification and Erosion and used to reveal the soil losses of our country were used.

#### **3.1 Rainfall erosivity factor (R)**

 A 329 minute Automatic Meteorological Observation Station (AMOS) data was used by the General Directorate of Combating Desertification and Erosion to obtain the rainfall erosivity factor. Furthermore, it was computed by means of the equation given below and taken from the rainfall erosivity power map of Turkey:

$$E = 0.29 \ast \left\{ 1 - 0.72 \, e^{(0.05l)} \right\} \tag{2}$$

where E is the unit rainfall energy and I is the rainfall intensity during the time interval.

#### **3.2 Soil erodibility factor (K)**

 23,000 profile data which was taken from 0 to 30 cm is existing in the soil information system established under the General Directorate of Combating Desertification and Erosion. By using the data and Eq. (3), obtained soil erodibility map of Turkey was put into account in this study area. The K factor map of the drainage basin is as follows:

$$\begin{aligned} K\_t &= 0.0293 \{ 0.65 \text{--} D\_G \text{+} 0.24 D\_G^2 \} \\ &\approx \exp \left\{ -0.0021 \frac{\text{OM}}{\text{C}} - 0.00037 \left( \frac{\text{OM}^2}{\text{C}^2} \right) - 4.02 C \text{+} 1.72 C^2 \right\} \end{aligned} \tag{3}$$

where Kt is the soil erodibility factor, Dg is the geometric mean particle size, OM is the organic matter content (%), and C is the soil clay content.

#### **3.3 Steepness and length of slope (LS)**

This data is obtained by using 1/25,000 numerical elevation model and Eq. (4). The map of steepness and length of the slope is given in **Figure 4**:

$$LS = \left(\frac{\varkappa \eta^{0,4}}{22, 13^{0,4}}\right) \ast \left(\frac{(\sin \theta)^{1,3}}{0, 0896^{1,3}}\right) \tag{4}$$

where x is the flow accumulation, θ is the slope in degrees, and η is the cell size.

#### **3.4 Cover management factor (C)**

 In order to get this data, forest stand maps produced by the General Directorate of Forestry and CORINE 2012 data sets produced by the Republic of Turkey


#### **Table 1.**

*Sediment delivery ratio equations [36].* 

 Ministry of Agriculture and Forestry Department of Information Technologies were used together. C values are assigned to obtained polygons [35].

#### **3.5 Erosion control practice factor (P)**

Erosion control practice factor covers the erosion measures in the study area. Any data could not be obtained for erosion control in Cakmak dam drainage basin. Therefore, this value is one for this study area.

#### **3.6 Sediment delivery ratio (SDR)**

 Sediment delivery ratio is the equation which countries produce for themselves and is often defined as a function of the area. In an effort to determine these values in our country, basin similarity test is carried out by using sediment observation station of the General Directorate of the State Hydraulic Works data and RUSLE equality results. In this study, USDA-SCS equation was used (**Table 1**).

#### **4. Results and discussion**

The Cakmak dam drainage area is 47,862.7 ha. Cakmak dam lake surface is calculated as 500 ha with GIS. The following calculations were obtained by removing the dam lake surface from the drainage area.

For the drainage area of Cakmak dam, the rainfall erosivity factor (R), soil erodibility factor (K), steepness and length of slope (LS), and cover management factor (C) were calculated and mapped by using the GIS-based DEMMS model. These maps were illustrated in **Figures 2–5**, respectively.

A map of the soil losses of displacement for the drainage area of Cakmak dam which is obtained by using the DEMMS model is shown in **Figure 6**. Besides, the map of transported soil losses by river is given in **Figure 7**.

From the results of the model, in the study area, 71.4% very low, 20.6% low, 3% moderate, 1.6% high, and 3.4% very high erosions were observed. Soil erosion classification, areas, and percentages are given in **Table 2** for Cakmak dam drainage area.

In the drainage area of Cakmak dam, 207.210 tons of soil is displaced as a result of water erosion (**Table 3**). This means that in the unit area, 4.38 tons<sup>−</sup><sup>1</sup> ha<sup>−</sup><sup>1</sup> soil is activated by the impact of water erosion.

 It was calculated that 97.920 tons of soil per year was carried by rivers in the evaluation made considering the sediment delivery ratio (**Table 4**). This means that in the unit area, 2.08 tons<sup>−</sup><sup>1</sup> ha<sup>−</sup><sup>1</sup> soil is carried by rivers.

**Figure 2.**  *R factor map.* 

**Figure 3.**  *K factor map.* 

Due to soil erosion, bathymetric surveys were used to analyze the effects of sediment transported to Cakmak dam reservoir. It was examined by the elevationvolume data belonging to before the dam construction of the Cakmak dam and in 2014. As a result of the study, it has been observed that an average annual load

**Figure 5.**  *C factor map.* 

**Figure 6.**  *Water erosion map.* 

of 0.59 hm3 sediment is carried by the river to the reservoir. The obtained value is approximately eight times higher than the amount of annual sediment carried by river calculated by sediment delivery ratio equation. This difference can be

#### *ISBS 2019 - 4th International Sustainable Buildings Symposium*


#### **Table 2.**

*Soil erosion characteristics.* 


#### **Table 3.**

*Water erosion values.* 


#### **Table 4.**

*Values of soil carried by river.* 

attributed to the excessive amount of sediment carried in flood conditions. In fact, the model result is a value close to the average annual sediment carried by rivers in Turkey. Generally, when the sedimentation observations are compared with the results of the bathymetry, the bathymetric values are higher. A similar situation is also present here. Besides, in this period, it was determined that the volume of the

dam had a loss of 8.17% dead volume, in the active volume of 30.23%, and storage loss of 14.39% in the total volume.

### **5. Conclusions**

 In the present study, the soil loss of the drainage basin of Cakmak dam was estimated. Factors affecting soil loss in the basin, the rainfall erosivity factor (R), soil erodibility factor (K), steepness and length of slope (LS), and cover management factor (C), were calculated and mapped by using the GIS-based DEMMS. The severity of soil loss was investigated in five categories. From the results of the model, in the study area, 71.4% very low, 20.6% low, 3% moderate, 1.6% high, and 3.4% very high erosions are observed. In addition to this, the amount of erosion caused by water and the amount of soil carried by the river were determined in the total basin area. In the drainage area of Cakmak dam, 2072.1 tons of soil is displaced as a result of water erosion. This means that in the unit area, 4.38 tons-1 ha-1 soil is activated by the impact of water erosion. It was calculated that 979.2 tons of soil per year was carried by rivers in the evaluation made considering the sediment delivery ratio. This means that in the unit area, 2.08 tons-<sup>1</sup> ha-<sup>1</sup> soil is carried by rivers. Although there was no high erosion in the basin, it was determined that water erosion and the amount of soil carried by the river had a negative impact on the operation of the reservoir. In 26 years, it was determined that the dam had a loss of 8.17% dead volume, the active volume of 30.23%, and storage loss of 14.39% in the total volume. The results show that if the measures are not taken related to water erosion in the area, the dam will have completed its useful life in approximately 25–30 years. Some measures should be taken to ensure that the Cakmak dam, which was built to meet the drinking water needs of Samsun province, can meet this need in the near future. For this purpose, it can be advisable to perform terracing and forestation work on erosion control in the upper basin. In order to remove the sediment deposited in the reservoir, natural and mechanical methods such as washing and underwater excavation can be applied.

### **Acknowledgements**

The authors are grateful to the Turkish Republic General Directorate of Combating Desertification and Erosion for their supports.

### **Author details**

Murat Pınarlık\* and Zeliha Selek Department of Civil Engineering, Gazi University, Ankara, Turkey

\*Address all correspondence to: muratpinarlik@gazi.edu.tr

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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#### **Chapter 56**
