*2.1. Pothwar Region and Study Watersheds Description*

Determining the relationship between rainfall, runoff, and soil erosion was imperative in the Pothwar rainfed region for creating applicable soil and water conservation mechanisms, as well as for enhancing crop productivity. Considering the long-term sustainability and productivity of eroded land, the present study focused on the Chakwal and Attock districts of the Pothwar plateau between 32◦30 and 34◦ north latitudes and 71◦45 and 73◦45 east longitudes, as shown in Figure 1. The region has an arid-to-semiarid climate with hot summers and cold winters [42]. The plateau land comprises broken gullies, low hill ranges, and a flat to gently undulating topography. The textural classification varies from sandy to silt and clay loam, and the land consists of poor-to-fertile soil derived from sandstone and loess parent material [43].

The rainfall pattern is unpredictable with a high intensity; 60–70% of the total rainfall occurs during the monsoon season (from mid-June to mid-September). The average annual rainfall varies from 250 to 1675 mm, with a decreasing trend from the north to the south. After rainfall, soil crusting decreases the infiltration rate and aeration and increases the soil strength, which reduces plant emergence and exposes the soil surface to erosion [44]. The soil loss rate becomes relatively high with higher intensity rainfall–runoff over greater slope lengths and steepness levels.

Out of the total 1.82 Mha of the Pothwar region, approximately 0.77 Mha (43%) are cultivated, and the remaining is mostly grazing land. Only 4% of the cultivated area has irrigated agriculture, while the remaining area is under rainfed agriculture [45]. Rainfall plays an important role in crop production. The principal crops of the area are wheat, maize, bajra, barley, pulses, groundnut, fruits, and vegetables. Without adequate protection, the effects of rainfall–runoff erosion on this highly erodible soil are severe, causing extensive fertile soil loss [19], endangered soil and water conservation structures, and reservoir depletion through sedimentation. Moreover, this raises doubts regarding the viability of existing and future soil and water conservation schemes.

The high rate of erosion creates a silting problem in the small dams of the Pothwar area. For the sustainable agricultural and socioeconomic development of the region, the government has started various projects for watershed development in the upstream of storage reservoirs, such as the Watershed Management Program by Pakistan's Water and Power Development Authority (WAPDA).

Similarly, soil and water conservation activities have also been carried out in the Pothwar region for erosion control and land development through a series of Barani area development projects. The application of the loose stone structures project of SAWCRI (Soil and Water Conservation Research Institute, Chakwal) with ICARDA (International Center for Agricultural Research in the Dry Areas) for erosion control resulted in the development of some environmentally friendly and cost-effective resource conservation technologies.

**Figure 1.** Location map of the Pothwar region, including the Dharabi watershed: Catchment-25; the Kohkar Bala, Chak Khushi, Khandoya, Ashraf Gully, Khaliq Gully, Dhoke Hafiz Abad, and Dhoke Dhamal micro-watersheds.

The soil and water conservation structures were installed in small terraced agriculture fields in the Chakwal and Attock districts by the SAWCRI Chakwal department. Seven small sites were selected to evaluate the effectiveness of these structures on soil erosion control. The description of these sites is given in Table 1, and a location map is shown in Figure 1. The demarcation of the watershed areas was a challenging task and was performed using a Global Positioning System (GPS) survey. During the survey, the point elevation data at different locations were collected within and at the boundary of the watersheds. Using the elevation data in ArcGIS, we performed a topographic analysis and observed that all the watersheds have a land slope of 2–7% where the crops are grown. The location of the conservation structures was also noted for use with the SWAT model setup.


**Table 1.** Study watershed site descriptions.

\* used for SWAT calibration and validation due to the availability of measured flow and sediment data.

#### *2.2. Soil and Water Conservation Structures*

In the Pothwar region, the terrace land use system and the wide and deep gullies are used for field crop production. The agriculture fields are usually not flat; however, various field terraces are situated at different elevation levels (Figure 2a). Farmers make earthen embankments (bunds) to retain rainwater and conserve soil moisture. When heavy rainstorms occur, the terrace land use system often fails due to the breaching of the field embankments/bunds. This is mainly caused by the hydraulic shear failure of the soil under saturated conditions. The disturbance of soil organisms can aggravate the impact. Figure 2b shows such terrace failures, which increase the surface runoff and soil erosion, especially in the Pothwar area.

**Figure 2.** Soil and water conservation structures: (**a**) Terraced cultivated lands in Pothwar. (**b**) Breached terrace bund/embankment. (**c**) Loose stone structures system. (**d**) A loose stone structure in the field.

The moving runoff from higher to lower fields takes not only the fertile topsoil but also essential nutrients and organic matter with it, thereby reducing the productive capacity of soils. If the breached bund is not repaired before next rainy season, it leads to the formation of gullies and renders the area out of plough, a great national loss. Crop yields on such eroded lands are poor, and the livelihood of resource-poor farmers is adversely affected. To reduce this problem, the eroded areas need sustainable rehabilitation to ensure food security in the region. With the collaboration work of SAWCRI and ICARDA, loose stone structures were installed in the upper, middle, and lower parts of terraced watersheds, as shown in Figure 2c,d.

The idea is to retain water in a terrace until a certain rainfall amount (without overflowing the terrace) and then to divert the excess rainfall in a non-erosive way. First, this increases the infiltration and improves the amount of plant-available water; secondly, it reduces soil erosion by reducing the amount and kinetic energy of the flowing water. On average, a water height of approximately 4–6 inches can be held back in the fields. The crest of the structures is kept raised 6–9 inches from the soil surface to encourage in situ rainwater conservation. The height of the sidewalls of a structure should be equal to the height of the field bund/embankment where the structure is to be installed. The cross-section view of these structures is shown in Figure 3.

**Figure 3.** Cross-section of a loose stone structure.
