by Jim Danisch
November 20, 2002

With the new Lower Mattole Fire Safe Council getting its start, there has been a lot of talk about increasing and improving water storage for emergency use in the dry season. Options for storage are tanks of various kinds, and ponds or reservoirs. This is my personal experience with ponds, which I hope will stimulate more discussion about water issues in the Mattole. If there is enough interest in the community, the MRC could consider having a "water storage and usage" workshop. Let the office know if you're interested.

My interest in ponds started when I was a kid, enjoying meditative hours by ponds and entering into the complex life that inhabits them. This was reinforced when, faced with figuring out a homestead water system, I realized that for the price of a 2500-gallon water tank I could get a pond with about ten times the volume -- and as a bonus, it would look good too. This pond ended up being 40 X 50 X 6 feet deep. It took a couple of hours of cat work to excavate an oval basin in shaly, porous soil in a bench on the ridge top. There is no way this porous soil will hold water without a liner. Options are:

· No liner: if you have clay soil and are near the water table
· Clay liner: usually bentonite mixed into several inches of soil before adding water to the pond. This doesn't work in porous soils.
· Ferro-cement: This is more labor-intensive than plastic, but has the advantage of rigidity.There are stories of a ferro-cement cistern that broke in half in the ’92 quake.
· Plastic of various kinds.

One certainty is that there are as many solutions as there are individual sites.

Eighteen people pull pond liner

The liner comes in an accordion-folded roll; for this pond it weighed about six hundred pounds. By backing my pickup slightly over the edge of the pond, it was fairly easy to slide it out and to get it laid and trimmed to shape with a utility knife with one helper. By contrast, the latest pond is 105 by 65 feet and 10 feet deep, and the liner weighed a ton and a half. Eighteen people managed it pretty easily. The liner I chose is 30 mil polyethylene, which is not damaged by cattle or deer (bears penetrate it easily).

Safety for animals and people

Safety with a plastic-lined pond is a serious consideration, both for animals and people. The liner is slippery, and it is almost impossible to climb out of a steep-sided pond. I’ve covered parts of the banks with pieces of throwaway carpet, which are anchored just outside the edge of the pond with 3/8 inch re-bar staples about 1 foot long. It is important to make these ramps long enough to go several feet into the water even when it is low. I haven’t researched it thoroughly, but presumably old carpet has completed outgassing. In a new pond, it provides instant habitat for insects and frogs.

It is fed by a couple of springs from some distance away. In the dry season, it just about keeps up with the garden, and provides a reservoir in case of fire. Although the springs are diverted, they have been left so wildlife can still get water. Like most surface springs in our valley, they are very small in the late summer, and probably most of the water escapes underground, not into my pipe. There is a small spillway, which never spills more than 10 feet down the porous hillside. Carpet has proven successful as a spillway liner -- after a year or two grasses grow through the carpet, but erosion is prevented. Since there is no chance for pond water to go directly into a stream, the pond is stocked with goldfish for beauty (and manure for the garden) and "mosquito fish" which eat mosquito larvae. The fish population is held in balance by garter snakes.

Utility and beauty improve life for water critters

Not only has the pond provided utility, but it has provided beauty: in the garden of course, but also through its general effect on our little piece of ridge top, which through the garden has provided habitat for multiple species of birds, mammals and insects that never came here before. The first year when it filled up, it was crystal clear and great for a swim -- you could go to the edge and look down to the Mattole several hundred feet below. The second year, it became a popular venue for all sorts of critters that either came down the pipe from the springs or came on their own feet: first small water beetles, then dragonflies and frogs (all card-carrying natives). A few pieces of Parrots' feather (an aquatic plant) were thrown in the water, and it now covers about 4/5 of the surface, keeping algae, which bloomed heavily the third year, to a minimum.

Besides water for irrigation and fire protection, the pond serves as penstock for a small hydroelectric system, that operates in the winter when there is enough rain to fill an intermittent drainage. A collector box with special no-clog screen feeds a 2-inch pipe to the pond. A standpipe and drain slightly above the pond bottom feed a 2-inch pipe to the turbine, which is about 120 vertical feet downhill (about 60 psi at the turbine, generating 6 amps at 24 volts with a ¼-inch nozzle). If there is not water coming into the pond, the turbine will drain it overnight -- about 30,000 gallons. Fortunately, our land is shaped so that I can turn the turbine on and off with a valve about 20 feet from our house.

Bear strolls out of pond after breaking standpipe

A new, much bigger reservoir high on top of the ridge, in a natural depression that we enlarged, is designed to catch rain water (about 200,000 gallons of it; the pond is 105 X 65 X 10 feet deep), and hold it for summer garden irrigation and for fire fighting. It failed to hold water the first winter, because of a bear who got in and tore small holes in the liner getting out, before I was able to install carpet ramps. Now that the ramps are installed, the bear was able to easily get in, break off a 3-inch PVC standpipe, and stroll back out. I’m re-installing it with a flex joint, which should at least make it easier to repair if the bear does it again.

If the winter rains are sufficient, there will be enough water to augment garden irrigation in the summer, while keeping a good reserve for fire protection. The purpose of the standpipe, besides filtering, is to ensure that water never goes below a certain point, in order to keep an emergency reserve and to keep the pond from going completely dry.

Evaporation is a factor in planning storage capacity; we don’t have much local data yet, but are collecting it. A small pond 20 X 30 X 5 feet deep with no input during the summer loses 2-3 feet of water.

Ponds that recharge aquifers after the rains

Recharge ponds that slowly perk into the river in the dry season are also an interesting idea, the success of which would be highly dependent on soil porosity -- it would be difficult to predict or control how fast water seeped out.


Are ponds harmful to the environment? It depends...

There are a lot of issues about ponds and their effects on the environment. On the positive side, they can:
· Collect excess runoff in the winter
· Distribute it in the dry season for fire prevention, irrigation, and groundwater infiltration. (Howard Orem of Petrolia has made many groundwater infiltration ponds.)
· Provide beauty
· Provide habitat for a rich variety of fauna and flora
· For your dollar, they hold much more water than tanks
· Holes can be mended easily with special sticky rubber tape.

Negatives are:

If poorly designed, a dam or berm could give way, causing significant erosion. This points to the need for expertise in pond design.

If a stream is diverted through a pond and then back into the stream, it can raise summer water temperatures, and also carry invasive species into the stream that may have colonized the pond. Ponds that capture springs or tributaries can keep that water from getting to the river as well as warming what does get by. Ponds of this nature have de-watered the Navarro River and are causing major problems in that watershed.

Water may be diverted from its natural course. (In our case, the hydroelectric system diverts water that ordinarily would end up in Cook Gulch, into Saunders Creek, which then enters the Mattole a bit farther upstream. It only does this when the turbine is running, which it does intermittently during the winter when there's enough water and no sun. There is so much water coming down the drainage where the turbine is located that the water it adds is a drop in the flood, so I don't think it has any effect on water quality, erosion, etc.

There is an issue about large pieces of polyethylene for disposal. Leftover pieces from trimming the edge can be used for small ponds, but there is always a certain amount of waste, and I have a stockpile of large scraps I haven’t found uses for yet. On the other hand, they aren't deteriorating, and perhaps in the future they'll be needed.

If not protected, animals or people could get in and drown, because of the slippery sides. Used carpet or fencing are solutions.

I’ve been told that ponds could attract invasive species, like bull frogs, which devastate natives. I’ve seen no evidence of this in our ponds -- there is rich life ranging from microscopic algae to the garter snakes that thrive on the tadpoles and insects. As far as I can tell, I'm the most invasive species on our ridgetop.

Ray Lingel comments: "My thinking is that the best pond might be one that captures rain water only, or only diverts a tributary or spring in the wet months. I think ponds are crucial for the future of the watershed."

In conclusion, I think that the positives usually outweigh the drawbacks, and that if you’re interested in conserving water in the summer, it’s worth looking into the option of installing a pond.





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Table of Contents for Mattole Restoration Newsletter, Issue 19 - Winter/Spring 2002-03