Those people probably never, ever tried to move gravel or sand around. Otherwise, they would know that if you want the ultimate tool that dissipates any mechanical energy, gravel and/or sand are exactly the materials you should look first. Just a brief look at any construction site or mining operation will show a number of energy-hungry technologies (excavators, bulldozers, trucks, transport belts and so on) used just to put the damn substances somewhere else. Diesel exhaust, dust, noise, people wearing helmets and half or 2/3 of the machinery always broken... priceless, environmentally-friendly picture. Compare that to an artificial lake used for recreation, sports, fishing, water supply for households and irrigation, flood control.. and somehow also storing electricity.