Construction workers were warned by the government yesterday not to dump waste illegally on slopes as it could create a landslide hazard in the coming rainy season. The number of illegal-dumping cases has been on the rise in the past decade, increasing from a few cases in the late 1990s to about 30 last year, Philip Chung Wai-keung, acting chief geotechnical engineer of the Civil Engineering and Development Department. 'Construction waste such as sand, stones and iron bars are loose and could easily be washed down like snowballs from the top of a hill during rainstorms,' he said, adding that it was difficult to spot some illegally dumped waste as it had already been integrated into the slope. He said illegal dumping was a criminal offence, and residents should report to the 1823 call centre immediately if they saw any. A promotional clip was launched yesterday on television and radio as part of an effort to step up public education on the dangers of illegal dumping. The department received 866 reports of landslides last year, a record high for the past 25 years. Among them, 70 per cent occurred on man-made slopes and 30 per cent on natural slopes. The majority affected squatters, footpaths, roads and open spaces. Meanwhile, the department has finished carrying out landslip preventive programmes on about 2,000 high-risk man-made slopes. Starting next year, the department will carry out preventive programmes annually on 150 medium-risk, government-owned man-made slopes and 30 natural hillsides, and will check 100 privately owned slopes. An amount of HK$600 million was set aside annually for these projects, said the deputy head of the geotechnical engineering office, Mak Shu-hei. One such programme has been under way at On Yam Estate in Kwai Chung since October 2007 and is due for completion in June. An amount of HK$6 million was spent on building a reinforced- concrete wall and baffles on the natural hillside, which were used to reduce the flow of debris. Department engineers said the measures could withstand a landslide of more than 1,000 tonnes.