4 years ago

Prognosis and mitigation strategy for major landslide-prone areas Varunavat Parvat landslide in Uttarkashi

Prognosis and mitigation strategy for major landslide-prone areas A case study of Varunavat Parvat landslide in Uttarkashi township of Uttarakhand (India)


Ladari and Kansen villages are again located over terrace deposits, further west of Uttarkashi town the villages of Badethi, Delesaur, Chamkot and Matli are again occupying the terrace deposits (Figure 4). Indravati river the another major stream in the area and left bank tributary of Bhagirathi river also has terraces and active flood plain which are often subjected to flash floods and severe bank erosion during rainy season. Land use Varunavat Parvat has dense pine forest on the ridges whereas the middle slopes of this hill are having open pine forest with few pockets of sparse scrub. During the past decades landuse changes have been conspicuous over the lower slopes of Varunvat Parvat due to urban sprawl of Uttarkashi township (Plates 1 and 8) and this area of natural vegetation mainly pine trees has gradually transformed into concrete jungle. Landsliding activity in 2003 has completely buried Bus Stand and nearby hotels and major part of Horticulture Colony, Masjid Mohalla and stretch of Rishikesh-Gangotri National Highway at Uttarkashi (Figure 6). The crop fields of Gyansu, Padull and Wasunga in the west of Uttarkashi township are developed over alluvial fan deposits. Crop fields of Dang village in the south of Bhagirathi river are developed over alluvial fan whereas the agriculture fields of Joshiyara, Mandwa, Kansen and Tiloth villages are developed over the terraces of Bhagirathi river (Figure 4). Landslide scenario in the area Pre and post landslide field investigations during August, 2003 and October, 2003 have revealed that the head-ward shifting and gradual enlargement of small slide zones and their merging with the nearby large active slide zone (Tambakhani slide) has transformed the former into large complex slide zone (Figure 5; Plates 1, 2 and 8). Three major active slide zones observed on the Varunavat Parvat are Tambakhani slide, Ramlila Ground slide and Masjid Mohalla – Horticulture Colony slide. Further west of the slide zones an active debris flow slide zone is also developed in Gyansu area. Some characteristic features of these slides are given below. Prognosis and mitigation strategy 633 Plate 8. View of Varunavat Parvat in August, 2003 with only single prominent active slide zone of Tambakhani slide is seen

DPM 17,5 634 Figure 6. Handsketch of Uttarkashi township showing active slide zones and damage to government buildings and commercial cum residential areas Tambakhani slide This translational debris rock fall zone has developed on the southern slope aspect of Varunavat Parvat in mid 1990s. According to locals some cracks and a small slide zone were developed in the upper reaches of Varunavat Parvat in the aftermath of 1991 Uttarkashi earthquake. This small slide zone gradually transformed into a large rock fall zone during the monsoon seasons of successive years. Presently this active rock fall zone has a total length of about 680 meters and a width of about 40 meters in the scarp area and 5-7 meters in the root of the slide (at the intersection of the slide zone with Rishikesh-Gangotri National Highway). Prior to the monsoon season of 2003 this was the only active slide zone (developed over Varunavat Parvat) which was affecting Uttarkashi township as rolling boulders and debris from this slide zone often caused road blockage on National Highway at Uttarkashi (Figures 5 and 6 and Plate 8). Ramlila ground slide During the cloud burst events of July/August, 2003 the Ramlila ground slide developed as a small slide zone of 30 meter width and about 40 meter length in the upper reaches of Varunavat Parvat in the close vicinity (about 50 meters east) of large active slide zone of Tambakhani (Plate 6d). This small slide zone witnessed rapid head-ward expansion during August and September 2003 and completely merged with the active slide scarp of large slide zone of Tambakhani on 23 September, 2003 and it was on this day that the boulders and debris material from Varunavat Parvat were first observed accumulating in the backyard of multi-storeyed hotels in the Bus Stand area of Uttarkashi township. Within a short span of 24 hours the Ramlila Ground slide transformed into a large complex slide and multi-storied hotels and commercial cum residential complexes around Bus Stand along with the 100 meter stretch of Rishikesh-Gangotri National Highway were buried under the huge volume of slide debris, which gradually extended to Ramlila Ground in the down slope of National Highway and large scale sliding activity continued till mid October, 2003. This large complex slide named after Ramlila Ground has a length of 720 meters (approx.) and the scarp and body portions of the slide are active furthermore, the foot of this slide is well

Disaster management strategy for potential slide zones of Kumarkhera in Narendra Nagar township of Tehri Garhwal district, Uttarakhand, India