Dr. Vance Kennedy has received the Distinguished Service Award from the Environmental Protection Agency for his work with the U.S. Geological Survey. Now in his nineties, Dr. Kennedy maintains an active interest in water and land use issues in California and especially in the San Joaquin Valley. The following essay represents some of his latest thoughts on water and the drought.
The immediate problem posed by the drought is to know a lot more about the distribution of groundwater, its chemistry, the amount being pumped by large wells, the interaction of surface and groundwater, and the effect of pumping on the water table of neighbors. Though it is now legally restricted, all such information should be publicly available.
Pinning down the harm to a neighbor’s water supply will not be easy. Nevertheless, knowledge of the porosity of the geologic column and an estimate of the specific yield at each well site should allow reasonable estimates of the effect of a well on nearby groundwater supply.
After all, if you are pumping more water than the water table drop in your well can provide, the water must be coming from your neighbor or another source nearby, and then you are responsible for damage to that neighbor or nearby source. Sounds like lawyer heaven!
But the alternative to litigation is for large wells to be able to destroy a neighbor’s water supply and hence their property, without responsibility, as can be done now. The situation will be widespread if this present drought continues.
After four dry years, it’s understandable that almost all concern is for these immediate problems, but there has been little discussion of what to do when this present drought is over, other than to build more and larger reservoirs. The basic assumption is that we will see more of the same as in the past; that is, occasional droughts interspersed with wet seasons.
What has been ignored is the great increase in population and hence water demand, the use of much more drip irrigation, which depletes the groundwater, and the insistence on charging more for flood irrigation, which will discourage the practice.
In the past, society took advantage of the inertia in natural systems. There were large volumes of groundwater which could be pumped by both cities and farmers, taking advantage of the huge volumes of water stored in permeable sediments eroded from the Sierras over many thousands of years. The future climate and water demand may be quite different from the past, and there is no significant discussion of how to handle groundwater storage then.
The state’s failure to recognize the interaction between groundwater and surface water has compounded the problem, as has the insistence by the Farm Bureau that every farmer could pump all the groundwater he wanted, on the assumption that there was no effect on the neighbor’s water. Any hydrologist will tell you that is completely wrong, but science is ignored when money and politics are involved.
It may take a truly major catastrophe to overcome the obstruction to accepting reality. We don’t appear to be there yet.
If we accept global warming as a reality, certain assumptions seem reasonable. There will be little, if any, snow to melt to maintain stream flow in the spring and early summer. What flow there is will be relatively warm and incapable of supporting cold water fish like salmon. Hence, efforts to keep salmon runs are a waste of water badly needed for other uses.
Politics will probably prevent these realities being accepted before major damage to farming and other water users occurs. A separate, but related problem, involves taking water from northern California for use in the state’s southern cities.
During major droughts in the future, assuming global warming, reservoirs will often be drained earlier in the year and surface water flows will be almost nonexistent. Groundwater will be the only viable source to maintain society. Fortunately, groundwater storage capacity is thought to be at least ten times that in surface reservoirs and it does not require much time or large sums of money to use it. The challenge is how to recharge it when storms occur.
Warming oceans have definitely increased water storage in the atmosphere and that has the potential to cause more intense storms in the future. The question is how to keep that water when it is available.
In the past, when big storms were expected, water was released from reservoirs to make space for flood control. That water flowed to the ocean because farmers were not flood irrigating in the winter. That can change if farmers use those reservoir releases for flood irrigation in the rainy season.
However, keep in mind that the reservoirs can hold only a fraction of the potential groundwater storage. That raises the question of whether storm water, during storms, can be routed through canals on to highly permeable soils to, in effect, greatly increase the “precipitation” on those soils. It seems quite possible. Harmful effects on plants would need to be explored and there is a possibility such research may be funded.
It Won’t Be Easy
But few things are as simple as first assumed. Storm runoff passing through reservoirs would deposit coarse soil particles in the reservoirs, but maintain finer particles in suspension. Those finer particles, when applied to very permeable soils during storm runoff would tend to clog those soils and make them less permeable, thus partially reducing the infiltration of storm water in the future. Such clogging of coarser water filters by fine material has been demonstrated experimentally. The problem should not exist for water standing long enough in the reservoirs to allow fine particles to settle out.
In the past, highly permeable sandy soils have ben unappreciated because such soils require much more irrigation water to support plants. In the future, such soils may be much more valued for groundwater recharge. Land use planners need to look ahead. Because vertical percolation to the water table is commonly slow, large areas of land must be retained for groundwater recharge and not paved over.
If, as seems quite likely, surface water in the Valley will become much less reliable and groundwater will become much more important, any one contributing to the groundwater reservoir in significant quantities for public use should be paid a reasonable fee. The challenge will be to reliably calculate the amount of water contributed. Anyone using groundwater in significant quantities would be charged. Farmers using flood irrigation in wet seasons would accumulate credits and use some of those credits for drip irrigation during droughts.
We do something similar with electricity now. If water becomes much scarcer, the same practice may occur with water. At present, society has not accepted the benefits of flood irrigation in maintaining the groundwater supply. That situation must change.
Scientists with the U.S. Geological Survey have estimated that over fifty percent of groundwater recharge in the Modesto area is due to flood irrigation water passing below the root zone of plants. So past flood irrigation has provided the groundwater insurance we now benefit from. The situation is quite different elsewhere in the Valley, where drip irrigation has depleted groundwater stores dramatically.