Rainfall engineering for droughts and floods

A University of Waikato scientist says we need to rethink the way we collect and store water.

Associate Professor Earl Bardsley says water engineering has traditionally focused on rivers, either as a household supply source or as a potential threat from floods and it costs many millions of dollars to upgrade river water to drink-quality and then reticulate it for urban supply. Dr Bardsley is proposing “rain engineering”.

“With this very dry period we’re experiencing, I’m proposing that when it does rain we collect rainwater for additional urban supply, but rather than collect it from roof run-off and storing it in tanks, we should divert the water into a soakage sump,” he said.

He says water tanks can be expensive and unsightly on small city-sections, but where ground conditions are suitable then a soakage sump and a shallow bore could be installed to supply gardening water. Water pressure would be provided by a small pump in the bore.

“An advantage here is that water soaking down past the root zone might be used a second time,” he said.

However, not all localities are suitable for the urban-well approach, so Dr Bardsley suggests it would be useful to construct town or city maps of the upper 20 metres of subsurface so individual households could make garden water supply decisions.

“In addition to mains water supply, section bores might also be installed at the outset by developers of new subdivisions as an added attraction to potential purchasers.”

On a larger scale, rain engineering could also aid flood control. “Particularly in Australia where floods often arise from large regions with low relief. In such situations there is the possibility to construct ‘rain banks’ to keep the rainwater in, as opposed to the much large-river flood banks that are supposed to keep water out.”

He says the rain banks would be in the form of a honeycomb of low bunds, so from above, the landscape after heavy rains would temporarily take the look of extensive paddy fields.

“In an arid environment like Australia, this would have the advantage of soaking to groundwater rather than water being lost to sea in river floods,” he said.