Pond Boss Forums POND CONSTRUCTION Selecting a site Ground Water Ski Lake

Hello all. I'm in Utah and considering developement of a ski/wakeboard lake community. Nutshell version... about 60 acre property just outside a small metro area of 130k population. Parcel is 2450ft wide, so just wide enough. I plan on two lakes with a peninsula between them. About 28 build lots between the lakes and another 45 around the outside.

Land is very flat. Currently farmland used for dairy farm crop and grazing. Not sure of soil content yet, but one thing is certain. The water table even now in late fall is very high. We haven't had appreciable rain for about 3 months and there are a couple low watering areas (about 3ft below grade)for the cattle that have standing water. There is also an irrigation canal running the perimeter of the property and the land comes with generous water shares if ever needed.

My questions are around a ground water lake. I would prefer not to have the lake level fluctuating +-36in depending on snowfall, because I want to maintain 16:1 grade at edges to prevent erosion. These are to be wakeboard compatible lakes at about 10ft center depth. I know the moment I hit about 3ft depth things are gonna start to fill up.

Even if clay content isn't quite high enough, sodium bentonite is mined nearby,and the economics of the developemnt can handle an application of as much as 5 lbs/sf to seal up the lakes. We can then divert from canal to maintain desired water level. But will the bottom of the lakes seal correctly with clay or bentonite given the fluctuating water table?

Thanks!

Do you have rights to the canal? Is the ground water from the canal?

Biggest mistake I see buyers making in the western states these days is thinking an irrigation canal is a "year round stream." as advertised by some less than reputable real estate brokers. Then said irrigation water gets put in a pipe, and unless you own it, the water is gone.

I've never done any good with bentonite. Either no luck or no skill. If somebody with expertise is local, I would start asking questions there. It has to be worked into the soil.

Thanks Dave. From what i understand, the truly effective method for bentonite is the "blanket" method in a dry lake. Layer of bentonite covered by compacted soil.

In that circumstance, does the inseeping groundwater have enough pressure to destroy the sealing capacity of the clay or bentonite?

I had another curiosity.

I always hear about people with groundwater ponds building for the max water level, then trying to figure out a way to keep them filled. What if i go the other direction. Build it to be full at low groundwater. Then use spillway and/or pump to discharge excess during wet periods. This property does have a canal to release storm/groundwater into.

Thoughts.

Around here nobody ever has rights to the canal structure. All of them fall in public easements. You have rights to draw from or discharge to it. This property has shares to draw from it, regardless whether it is piped later. I can also purchase additional shares. For example, someone is trying to sell 3000 water shares right now for about $1k each. That is a huge amount of water. Could operate a 5,000acre farm with that.

Given the surrounding areas, im absolutely certain the standing water on the property is groundwater and not coming from the canal. In fact, this time of year the canals have all been closed. I'm actually confident that the water currently in the canal is groundwater seepage as well.

Brett,
Do you have soil samples down to 15 feet or so? If it isn't the type of clay that you can make pottery with then you really need to think hard about a liner.

Do NOT trust bentonite. You will have a leaky empty pond. Really nothing is a sure thing outside of proper constructed clay liner (meaning several layers of clay, each with the correct water/clay consistency and each properly compacted with special equipment), or, with a mechanical liner.

Some have made their own liner with used billboard tarps glued together. A commercial liner is going to be very costly.

If you have some clay to work with onsite you may want to search the forum about a polymer sealant. It may help slow the leak substantially, but again since you are in the planning phases rather than salvage phase after your pond starts leaking, I would plan to do it right or not do it at all.

Hauling in clay sounds like not an option in your geographic area?

Water can be pumped in so it doesn't sound like water access is the main issue, it is keeping it in place. I would dig a bunch of test holes down as deeply as possible and see what you find.

Not in a position to do test pits yet. The geologic surveys for that area lists the predominant soil structure as;

0-13"... heavy silty clay loam- firm sticky and elastic.
14-60"... silty clay- very hard,very firm, sticky and plastic.

This entire valley used to be part of prehistoric Lake Bonneville. So essentially we are talking about the flat bottom of a huge silty clay lake bed.
But I'm most concerned about fluctuating groundwater. I know that the water table is near the surface. The parcel is surrounded by housing developments. It is very typical for homes to have full basements here, but in this area they are all raised with daylight basements so the footings only go 36" below natural grade. If they went any deeper they'd have flooded basements every spring.

So I'm wondering if i should be more worried about water seeping in rather than water seeping out.

Brett, bentonite is supposed to be mixed with the soils.