Dehradun, Sept. 1 -- Heavy rain accompanied by thunderstorms, lightning and gusty winds lashed several parts of Uttarakhand, triggering fresh landslides, debris flows and land subsidence and leaving 87 roads closed across the state, even as the India Meteorological Department (IMD) issued an orange alert for Dehradun and Tehri districts for September 1. According to the public works department's (PWD) officials, 15 roads each were blocked in Chamoli and Pithoragarh, 11 in Tehri, nine in Pauri and five in Dehradun, while road clearance operations were underway at several locations. The situation remained particularly concerning in Mussoorie, where fresh land subsidence and soil erosion damaged the Mussoorie-Dehradun highway near Pani Wala Bend. A portion of the road, which had already suffered damage earlier this month, caved in further following heavy overnight rain and a strong surge of water through rain-fed drains. The administration imposed a one-way traffic system on the affected stretch. Vehicles travelling from Mussoorie towards Dehradun were diverted towards Kimari Road from Gajji Bend, while only light vehicles from Dehradun were being allowed to cross the affected section. Police personnel were deployed to regulate traffic. JCB machines were pressed into service to clear debris, but the continuing threat of landslides and slope instability remained a concern for residents and businesses located close to the highway. Local residents said damaged British-era drainage channels had aggravated the problem by failing to safely carry rainwater away from the slopes. Deepak Rawat, a local resident and restaurant owner, said a perennial spring-fed stream beneath several hillside residences becomes highly turbulent during heavy monsoon rain, eroding the hillside and threatening the highway. He said protective embankments washed away during flooding on September 16 last year had not been repaired, allowing the stream to continue cutting into the base of the slopes. Rawat said the old drainage channels that once diverted runoff into major ravines were now damaged and filled with debris. As a result, water accumulates on the upper slopes before seeping through cracks in the rock faces and flowing down towards the highway. Rohit Prasad, a Mussoorie resident, said the road section that had already been damaged and was under repair had deteriorated further. He said continued rainfall could pose a serious threat to residential buildings....