In South Africa at the start of my consulting career, I was called in to limit erosion from an old sandy pile of tailings close to the city. Vegetation would not grow in the acid materials that were cemented by negative pore pressures to a hard crust. We read all the literature of the seventies but found no answer. The gut feel solution was to cut a series of benches, one-foot high by one-foot wide, with vertical and slightly inward-sloping near-horizontal surfaces. Rain fell on the near-horizontal benches, ponded, and seeped into the tailings. Nothing ran off and erosion was controlled.

On other nearby tailings piles, wind erosion gave rise to vast dust clouds that blanketed roads and buildings in the dry season. In vain we tried vegetation; soon enough it was dead and ineffective. We tried furrows and berms to break up the wind, but to no avail. Finally in desperation, we spread cement and ploughed it into the upper surface, making a crust of cementitious soil. It worked, the dust subsided, the surroundings were spared, and the cost was low. I do not know if this system is still used.

In late 2004 I was on a team sent to assess burnt areas of San Diego affected by brush fires. Our mission was to specify what should be done to prevent impending rains from washing down the soil, causing mud slides, and damaging homes, businesses, and traffic. It was obvious which areas were vulnerable to catastrophic erosion: those steep hillsides where no vegetation remained and all was but ash, where there was little gravel and mostly sand and silt, and where there was both a large upstream catchment area and a vulnerable house or road downstream.

We specified and installed the following: spray commercial green stuff where the soil was vulnerable to washing away; sand bags to impede gully development; rock dams to create settlement ponds; and fences to catch the rocks that would otherwise have crashed onto busy roads. By the time we were halfway done, the countryside had turned an artificial green, every jute bag in the county was filled with sand and aligned along a ditch or road, and the clogged and filled sediment ponds emptied in anticipation of a new inrush of mud. It rained, and along a busy residential road, the mud and ash came down in a three-feet-high wall of gunk, pushing trees and debris and covering driveways and ditches. An impressive sight, and to the credit of the county road folk, quickly cleared. Not a house nor a car was mud bespattered.

In Idaho I looked over a heap leach pad that was contour-ploughed. What little rain fell and all the annual snowmelt ponded in the troughs created by the contour ploughing and that is where there was sparse vegetation. A few runs of UnSat-H and we convinced ourselves that the ponding water did not translate into infiltration or leachate (seepage), but instead the moisture entered the upper few feet of soil, stayed in the soil pores, and from there was evapotranspirated by the vegetation. What a good way to manage runoff and erosion!

A drive across country gives a good perspective on the commercial products well marketed to road departments. Depending, no doubt, on the preferences of the local engineers and the persistence of particular salesmen, you will see acres of matting, hay bales, silt fences, sand bags, and stakes. They are so neat and tidy and vulnerable.

I have walked large areas of the west with a geologist who has specialized in geomorphology. We have sought erosion barriers and baselines: those dikes and sills that impede erosion and that effectively establish a baseline to upstream topographic change. We have speculated on the events that will break and remove these erosional baseline features and tried to quantify the resulting impact on upgradient topography and hence the integrity of closed uranium mill tailings piles. I recommend a visit to the UMTRA website where you can access the Environmental Impact Reports and engineering design calculations that detail our efforts.