Nader Saadatkhah

Hulu Kelang, Malaysia regional mapping of rainfall-induced landslides using TRIGRS model

Rainfall-induced slope failure is one of the most destructive natural disasters that occur frequently in natural or engineered residual soil slopes. Rainfall-induced slope failures often occur as a shallow slope failure, with slip surfaces orientated parallel to the slope surface, especially in Hulu Kelang areas where a residual soil profile has formed over a bedrock interface. The possibility of using the transient rainfall infiltration and grid-based regional slope stability analysis method (TRIGRS) is applied to unstable slopes and three rainfall threshold chart conditions that result in landslides in the study area. We compare the intensity–duration of 3-day rainfall threshold charts (I–D)3, cumulative 30-day rainfall–number of rainy day (API30–N), and cumulative 3-day rainfall–30-day antecedent precipitation index threshold chart (E3–API30) conditions capable of producing slope instability in the study area predicted by TRIGRS, with empirical rainfall I–D thresholds for possible landslide occurrence in the northeast part of Kuala Lumpur. The results showed that TRIGRS is capable of reproducing the frequency of the size of the patches of terrain predicted as unstable by the model, which match the frequency size statistics of landslides in the study area, and the rainfall threshold based on the E3–API30 threshold chart could give a better prediction to a landslide than other conditions in Hulu Kelang area. Our results are a step towards understanding the mechanisms that give rise to landslide regional modeling.

Regional modeling of rainfall-induced landslides using TRIGRS model by incorporating plant cover effects: case study in Hulu Kelang, Malaysia

The objective of this paper is to develop a spatial temporal regional modeling of local rainfall patterns effect on the plant cover slopes in Hulu Kelang area. Rainfall interception, tree root cohesion, and tree surcharge were considered as main plant cover effects on the slope stability. In this regard, an improved version of the Transient Rainfall Infiltration and Grid-based Regional Slope stability model (TRIGRS) was performed using Microsoft Excel® and GIS framework system for coupled hydrological–mechanical modeling of rainfall-induced landslide by incorporating plant cover effects. The infiltration process of the improved model was integrated with the precipitation distribution method and rainfall interception approach while the slope stability analysis of TRIGRS model was replaced with the improved analysis with consideration of root cohesion and tree surcharge. In the following, the spatial temporal analysis of slope failures was performed using the monthly average rainfall during two different monsoon seasons of 2008 and 2009 for triggering shallow slope failure in Hulu Kelang area. The corresponding changes in pressure head and consequent water table depth were calculated during two monsoon seasons. Subsequently, factor of safety is computed using local rainfall patterns, along with root coefficient and tree surcharge in the study area. The results showed the plant-covered slopes are inducing an overestimation of the slope failure susceptibility using existing TRIGRS model, while the improved model resulted that less landslide susceptible areas were more representative of the actual stability conditions of the slopes at the study area.

Land Use Change Effects on Extreme Flood in the Kelantan Basin Using Hydrological Model

Land use and land cover (LULC) change results in increased of flood frequency and severity. The increase of annual runoff which is caused by urban development, heavy deforestation, or other anthropogenic activities occurs within the catchment areas. Therefore, accurate and continuous LULC change information is vital in quantifying flood hydrograph for any given time. Many studies showed the effect of land use change on flood based on hydrological response (i.e., peak discharge and runoff volume). In this study, a distributed hydrological modeling and GIS approach were applied for the assessment of land use impact in the Kelantan Basin. The assessment focuses on the runoff contributions from different land use classes and the potential impact of land use changes on runoff generation. The results showed that the direct runoff from developmental area, agricultural area, and grassland region is dominant for a flood event compared with runoff from other land-covered areas in the study area. The urban areas or lower planting density areas tend to increase for runoff and for the monsoon season floods, whereas the inter-flow from forested and secondary jungle areas contributes to the normal flow.

Impact of land cover change on the environmental hydrology characteristics in Kelantan river basin, Malaysia

Changing the land cover/ land use has serious environmental impacts affecting the ecosystem in Malaysia. The impact of land cover changes on the environmental functions such as surface water, loss water, and soil moisture is considered in this paper on the Kelantan river basin. The study area at the east coast of the peninsular Malaysia has suffered significant land cover changes in the recent years. The current research tried to assess the impact of land cover changes in the study area focused on the surface water, loss water, and soil moisture from different land use classes and the potential impact of land cover changes on the ecosystem of Kelantan river basin. To simulate the impact of land cover changes on the environmental hydrology characteristics, a deterministic regional modeling were employed in this study based on five approaches, i.e. (1) Land cover classification based on Landsat images; (2) assessment of land cover changes during last three decades; (3) Calculation the rate of water Loss/ Infiltration; (4) Assessment of hydrological and mechanical effects of the land cover changes on the surface water; and (5) evaluation the impact of land cover changes on the ecosystem of the study area. Assessment of land cover impact on the environmental hydrology was computed with the improved transient rainfall infiltration and grid based regional model (Improved-TRIGRS) based on the transient infiltration, and subsequently changes in the surface water, due to precipitation events. The results showed the direct increased in surface water from development area, agricultural area, and grassland regions compared with surface water from other land covered areas in the study area. The urban areas or lower planting density areas tend to increase for surface water during the monsoon seasons, whereas the inter flow from forested and secondary jungle areas contributes to the normal surface water.