**3. Methodology**

*3.1. AHP for Landslide Susceptibility Mapping*

The production of a landslide susceptibility map of the whole area to predict the possibility of landslide occurrence was carried out to determine landslide high and lowrisk areas using the AHP method. Professor Thomas L. Saaty originally developed AHP as a multi-criteria decision-making (MCDM) approach [66]. Applying AHP in this study aims to identify, correlate, weigh, and rank different parameters that determine slope susceptibility to landslide [86]. The method assigned weights to the conditioning factors by pairwise comparison. This pairwise comparison creates judgments between pairs of the set of variables instead of prioritizing them. The conditioning parameters associated with the study area and essential to assess landslide susceptibility are significant in achieving this judgment. The conditioning factors were ranked between 1 to 9 according to their level of importance. AHP is one of the most widely successful GIS-based methodologies for landslide susceptibility mapping over the past decades [52]. This is due to its ease of use and high capabilities in providing prediction maps [87]. It uses the consistency ratio (CR) to identify consistencies by comparing the priorities of each criterion using the CR equation, according to Saaty [62].

$$\text{CR} = \frac{CI}{RI} \tag{1}$$

where *RI* the random consistency index and *CI* represents the consistency index expressed as

$$\text{CI} = \frac{\lambda \max - 1}{n - 1} \tag{2}$$

where *λmax* represents the principal value of the matrix, *n* is the order of the matrix. Moreover, the weights of each criterion were integrated into a single landslide susceptibility index by applying the equation:

$$LSI = \sum\_{i=1}^{m} \text{Ri} \times \text{wi} \tag{3}$$

This decision-making tool specifies the value of each factor. Where Ri represents the rating classes of each layer, and wi represents the weight of each of the landslide conditioning factors. Each factor's weight from the matrix class was multiplied by the weight class. The local representation of elements in the slope area where landslide is predicated determines the susceptibility of map results.

#### *3.2. Field Experimental Design*

We carried out the hydroseeding experiment on the 11 August 2020 within the study area on a terrain sloping at 65◦ with a total horizontal surface area of 304 cm and a total vertical area of 244 cm wide and divided into four equal parts of 61 cm each, as shown

in Figure 3. The site was leveled and tilled with a rake to remove large soil particles. We studied the nature of the soil and climatic condition and did not modify the earth as this may alter the experiment results. Seed samples of 1 kg each were separately mixed with 500 g of fertilizer and 50 mL of seed germinator mixtures before the hydroseeding experiment. The mixtures were sprayed with an Ozito cordless hand spreader.

**Figure 3.** The spraying process on the study area.

#### 3.2.1. Vegetation Ground Cover

Vegetation ground cover has long been adequate, especially in reducing landslide and erosion on the roadside slopes [88]. Vegetation cover promotes infiltration and provides resistance to topsoil by stabilizing the soil structure and intercepting rainfall and runoff, thereby playing a vital role in soil and water conservation [89]. A related approach to stabilize disturbed slopes is by hydroseeding. In this research, we used the line-based method to measure the vegetation ground cover. Geometrically, it is a single-dimensional distance line measurement that measures the distance of the first contact to the last touch of the species. It also determines the percentage cover for each line then averages the lines together to estimate vegetation cover. The formula of the line-based method is as shown below.

$$\% \text{ground cover} = \frac{\text{Total distance of specific } A}{\text{Distance of all specific along line}} \times 100\tag{4}$$

When the vegetation ground cover is denser and complex, the surface is shielded from wind, and direct rainfall is intercepted and redirected by the canopy.
