water diversion
Photo: Shutterstock.com

By Scott Hamilton, President, Hamilton Resource Economics

Biological mechanism. Fish, even at the youngest life stages, have a natural buoyancy that keeps them suspended in the water column. As long as the downward velocities are sufficiently slow, the fish will maintain their position in the water column, and water can be removed from the water body with no impact to the fish. Experiments with larval delta smelt have determined safe operating velocities. Large quantities of water can be diverted with fish friendly diversions because the infiltration area is hundreds of times greater than that of conventional vertical screens, allowing for much lower water velocities.

More and more farmers and water managers are faced with a tricky problem – how to divert water from a river without harming fish, especially endangered fish, that inhabit those waters. The problem has become particularly important lately as water managers seek to capture flood flows from rivers to recharge aquifers – an important tool in helping to achieve groundwater sustainability. In western Madera County, for example, water districts and farmers are looking to divert San Joaquin River flood water from the Chowchilla Bypass, but because salmon are being restored to San Joaquin, farmers are being required to build expensive fish screens.

In the Delta, the problem is more significant. Both the State and Federal Water projects have elaborate fish screens to prevent fish from being entrained in the pumps. The screens at these facilities divert fish to holding tanks where they are held temporarily and then returned to the Delta. Millions of fish are salvaged annually. But some of the smaller and more sensitive species are entrained in the process. That is, they are preyed upon by larger fish before they reach the salvage facilities, they are not diverted by the louvers intended to direct them to the salvage facilities and are killed at the pumps, or they are salvaged but die during the capture, handling and return process. SWP’s Skinner fish facilities, constructed from 1966 to 1970, are now 50 years old. While state-of-the-art at the time, conditions and species of concern have changed. Even if they do not die, the Endangered Species Act prevents harassment of species without a permit.

Project concept for the Delta. Infiltration beds – large areas with buried perforated pipe – could be constructed on subsided Delta islands. Tidal and river flows would pass over the infiltration galleries so there is no “dead-end”. Rather the facility would appear to fish like any other Delta channel. As pumps operate, water flows from the infiltration beds into collector channels, through a main pump station and into conveyance facilities for delivery. The infiltration galleries could be constructed in pairs to allow one gallery to be closed for maintenance while the other one continues to operate.

How do water managers protect a small and delicate listed fish while still delivering water to wildlife refuges, communities, and farmers in central and southern California? It’s a tricky give-and-take as water managers seek to operate in such a way as to avoid jeopardizing endangered species and convince regulatory agencies that their operations are reasonable, thereby obtaining the necessary permits to continue pumping under their respective contracts and permits. The give-and-take to date has resulted in very substantial reductions in pumping to protect fish frequently from January all the way through June–the period when inflows into the Delta are the highest. And in drought years like this one, the consequences are onerous.

A group of water districts in Kern and Kings County formed the South Valley Water Resources Authority and their managers have been tackling this problem for several years now. With the financial support of their water districts’ boards and the farmers that contribute financially to those districts, they have come up with an intriguing solution.

Conventional fish screens are located on the side of the water column and have a number of problems. The speed at which water approaches the screens must be sufficiently slow so that young fish don’t get pushed up against the screens and die. The holes must be small enough so that fish don’t go through them, and if the holes are that small, they are always clogging up, which means they have to have an automatic cleaning system. And of course, they can’t be made of regular steel, because that would rust. The use of vertical fish screens has resulted in expensive but not entirely satisfactory diversions. So, what is the alternative?

The answer the water district managers came up with was to diver the water from the bottom of the water column, not the side, dubbing this concept “Fish Friendly Diversions.” Imagine a number of perforated pipes buried in the substrate of a river (see Figure 1). Many farmers are familiar with a tile drain system, and that’s essentially what this is. The water is taken from underneath the water column creating a physical barrier between the fish and the pipes. But that is not why the system works so well. Fish, even the most delicate of fish–delta smelt only a few days old–have a natural buoyancy. They don’t sink but remain in the water column, so long as the downward velocities are sufficiently slow.

The concept of diverting water from the bottom of the water column in sensitive ecosystems is not new. The concept is currently in use in at least four rivers in California, and in the United States has been used to supply some communities with water for more than eight decades. But these facilities are typically very expensive to build, requiring horizontal boring underneath the body of water. But several rivers in the San Joaquin Valley have reaches that are not wet all year round, meaning that facilities could be constructed when that reach of the river is dry, making construction far cheaper. With the right media covering the pipes, it is estimated that an acre of fish friendly diversions could divert 60cfs. Construction during dry conditions also works in the Delta where these facilities can be constructed on subsided islands and then portions of exterior levees removed to allow the free flow of water across the pipes and protective media (the infiltration gallery).

Fish Friendly Diversions are intended to complement, not replace, other Delta Conveyance Facilities currently under consideration. A delta tunnel, for example, offers water quality and security that Fish Friendly Diversions cannot provide but at an expense that many in agriculture find difficult to afford.

The investigation of Fish Friendly Diversions to date has been funded by the South Valley Water Resources Authority whose members receive water from the State Water Project. They have expended more than $1million on teams of consultants to develop the concept and the work continues. Their progress is a testament to what can be achieved by working together to develop innovative solutions to address some of our most challenging issues.