Dr. Vance Kennedy is an award-winning scientist who had a distinguished career at the U.S. Geological Survey. Though long-retired, he follows current water issues closely and has become very concerned that the rush to conserve water via drip irrigation ignores the recharge benefits of flood irrigation, especially in those areas with highly permeable soil of the kind typical near Modesto.  Here, he takes exception to a recent article in the Modesto Bee.

Recently, the Modesto Bee estimated that the Modesto Irrigation District (MID) has been subsidizing farmers who use flood irrigation by about $100 million dollars over an unspecified period of time. The figure is a gross misrepresentation.

Over the last ten years, total value of farm production in Stanislaus County was a little over $28 billion, and over twenty years, about $42 billion. Let’s assume twenty percent of production used MID water, or $5.6 billion for ten years and $8.4 billion for twenty years.

That crop production is often estimated to stimulate three times as much economic activity locally as its initial value. Hence, farm production dependent on MID water may have caused as much as $16+ billion over ten years or $25 billion over twenty years. Not bad! So the return on investment on $100 million for ten years was 160 times and for twenty years it was 250 times! And there were other benefits.

We need to remember that groundwater is our ONLY reliable source of water during prolonged droughts. Hence, it really is priceless. Second, in a 2004 report by the U.S. Geological Survey, it was estimated (and it was only an estimate) that almost sixty percent of groundwater recharge in the Modesto area was from flood irrigation by local farmers. Given these figures, it is imperative local farmers continue flood irrigating for the benefit of everyone, despite the increasing popularity of drip irrigation, which depletes ground water rather than recharging it.

Prior to 1994, Modesto depended solely on groundwater for all its water needs. Thereafter, the city obtained about half its supply from surface water, the other half from groundwater. During the current drought, groundwater usage is up and will increase even more if this El Nino doesn’t help dramatically. It follows that the city of Modesto should be encouraging farmers to flood irrigate, and that includes keeping the cost of irrigation water very low.

Vertical permeability of soil and rocks in the Modesto area ranges widely. In order to recharge groundwater, one needs large areas of permeable soils and appropriate flooding, which farmers have provided in the past. A major reason for that flooding was the water was very low cost. Where feasible, the city, county, and irrigation districts should also maintain large settling basins to recharge groundwater when surface water is available.

When farmers are accused of not paying their fair share for water, many factors have been left out of the cost equation, including how much of flood irrigation is lost to evaporation and transpiration. The amount of water that moves below the root zone and recharges groundwater is available for use by others than farmers, including cities and industries, at very little cost. The cost to the farmer to maintain equipment and labor to apply irrigation water has been ignored, but shouldn’t be.

It seems reasonable that the entities that benefit from flood irrigating should bear the costs of these benefits. Farmers benefit from water to support their crops, and cities and others benefit from the recharge to groundwater. It is their insurance during prolonged droughts.

In the past, that insurance benefit has been paid by a surcharge on electric bills (the so-called subsidy referred to by the Bee) which everyone pays. The Bee continues to ignore the value of farmer-supplied groundwater, which is used by everyone in addition to farmers. It also ignores the insurance value of that groundwater in times of drought.

A key point is that, to the extent that flood irrigation rates increase, it will encourage more and more drip irrigation, thereby depleting groundwater and reducing immensely valuable groundwater storage. That can be a recipe for future disaster with global warming and it will happen long after present politicians are gone. The adage, “There is no free lunch (or water)” is highly appropriate.

With global warming, there will be less snow in the mountains to maintain late spring and early summer runoff. Heavier rains are expected due to warmer oceans. Only limited amounts of such heavy rains can be stored in a short time. Population growth in the Valley will increase water demand, and farmland providing groundwater recharge will be paved over.

There is an urgent need to consider what the population carrying capacity is for the Valley under major climate change. We are no longer in a frontier situation. Prolonged droughts are a real possibility and should be planned for.

If we are to encourage groundwater recharge, we need to have a better understanding of the hydrology of groundwater recharge and the interaction between surface water and groundwater. That means measuring, to the extent feasible, the movement of water below and above ground.  That will require money and new technology.

Water is going to cost much more for everyone and groundwater economics is now a focus for discussions of water in general. The distribution of costs must reflect actual costs and benefits in toto, and that can only happen with much better hydrologic understanding and acceptance of the extremely valuable role flood irrigation plays in providing water for the whole community.