Pond digging with backhoe - was it well done?

My wife and I have a farm in the Colombian highlands, and as some of you may know, the country was hit recently by a severe drought event. In order to be more drought-proof, we decided to hire (April 2016) a backhoe to dig us a pond, which would be connected to a swale.

We first marked the pond perimeter, which has a rectangular shape, about 8m long, 4m width, and 3.5m deep (for the deepest section). The soil has a high clay content, which is good for sealing.

The terrain is quite flat, therefore we just built a small dam.

The backhoe driver already had experience making ponds, which may explain why he dug the side walls so steep. That was actually my concern: I thought the side walls should not be so steep so the backhoe could drive back and forth on them to compact them. In this case, the driver just used the shovel of his machine to "compact" the walls.

My concerns were not justified, as a few days later the pond was half full, and now it's almost totally full, probably by a mix of runoff and groundwater.

As for now we did not see any overflow from pond to swale or vice-versa. By the way, the spillway of the whole system is located in the middle of the swale.

What do people with experience with this kind of earthworks think about it? was it well done? would you have done it differently? I guess we'll have to wait until the next dry season (December-March) to see if there is any infiltration.

all the best

greg

It looks steep to me. My research indicated a 45 degree angle was the best. i can't remember the source.

I had to seal mine with clay. At your angle all the clay would run to the bottom and the pond would no longer hold water. Since yours is clay, you don't have an issue with its water holding ability.

I could see it getting wider and shallower over time, as the clay falls down the sides.

Hi Greg,

We're in Colombia too, and it seems that steep cuts are how they dig ponds and dams here. In our experience it depends on the terrain if this works out well for holding water. Our biggest dam holds water reasonably well, it looses about a centimeter per day, because of seep. Another one has more problems, it got a meter of water about a month ago, and it was dry again 3 weeks later.

Advised slopes for dam walls are 3:1 inside and 2.5:1 outside, compacted. For ponds without a wall, we'd advise any slope the machine can still drive on. Compaction by the bucket or the shovel only goes so far, better have the machine drive on it. That said, the soil around the pond can make a big difference on if it matters much or not. I guess within a month you'll know if it retains the water or not.

Me personally, I would have done a shallower angle on one side of the pond. Not for any other reason than to give easy access to wade into the pond if needed. Standing on the edge of a 45 degree slope knowing if you step into the water your going to slide right down to the bottom just isn't too appealing to me.

I agree, those steep sides could be a deathtrap.

I agree that the steep sides are not going to be forgiving to those who would wade or swim or fall.

From the engineering stand point it seems like the kind of soil and subsoil that surround the pond are considerations in whether or not it's going to hold water, hold together or silt in.  Another  thing about whether it will get shallower, or at what rate it will get shallower is what kind of water flows into it.  If it is clear ground water, then it's not carrying sediment in. If your run off that fills it is through vegetation, and at a slow ish rate, it's not likely it will carry a lot of sediment.

I get water from the Gunnison river, through an irrigation company.  I get to see all kinds of water, carrying varying amounts of sediment.  This we also can see in the rivers in this part of the country.  You can tell where it rained yesterday by what color the river is today, or whether it has not rained at all.  

When the irrigation water is running fairly clear, it's a good time to fill my cistern.  When it is carrying a lot of sediment it is fine to run it down my ditches, but not into the pond or cistern... for obvious reasons.  And I think the same will be true in your pond.  It will silt in if it is filled with sediment laden runoff.  

If you do find there is a lot of sediment carried into the pond, possibly there would be a way to get the water to drop its silt before it gets to your pond, or maybe you want  the sediment in the bottom of the pond.

It seems like it's a functional pond with a few elements to develop further depending on what develops.

Depends so much on purpose. I would not choose to design a pond like that for many reasons. Questions about water holding ability would be the least of them. That design offers minimal edge, it offers no safe entry and no exit, it offers no variety for aquatic life. I cannot see it being useful for anything but holding water and a pond is so very much more than just a water bucket.

The reason one would construct a steep sided water retaining pond is to prevent loss of water due to evaporation.  Especially run off ponds that don't have a consistent source of water such as a stream or spring.  Large gentle sloped shallow bodies of water/ponds dry up very quickly during drought conditions.  Steep sided ponds with the least water surface exposed to the air hold water longer.  When I had my run off pond built years ago, the dozer operator understood that principle and I ended up with a long pond about 8 feet deep in the middle that had steep sides and sloped at either end.  Much like the one in the pictures.  It really ended up being the best of both worlds holding water and having a sloped shore line.  It does lose several feet of water during the summer, but fills quickly and stays filled during the rainy weather.          

Ernie Schmidt wrote:The reason one would construct a steep sided water retaining pond is to prevent loss of water due to evaporation.  Especially run off ponds that don't have a consistent source of water such as a stream or spring.  Large gentle sloped shallow bodies of water/ponds dry up very quickly during drought conditions.  Steep sided ponds with the least water surface exposed to the air hold water longer.  When I had my run off pond built years ago, the dozer operator understood that principle and I ended up with a long pond about 8 feet deep in the middle that had steep sides and sloped at either end.  Much like the one in the pictures.  It really ended up being the best of both worlds holding water and having a sloped shore line.  It does lose several feet of water during the summer, but fills quickly and stays filled during the rainy weather.          

But that is why in areas where evaporation exceeds precipitation you want to store water in the soil, not on top where it can evaporate.  And yes, minimize surface area to minimize evaporation

My issue is not in the construction (shallow sides cause cattails to grow too), but the machine. You really need a dozer to build a pond. A backhoe can excavate a hole, but its the blade sliding over the pond's soil that makes it sealed. A dozer compacts as well as presses the soil and thus seals it. Its okay to use a backhoe or excavator to remove the soil, but the final shaping; that needs a bulldozer to be done properly. It is actually why a lot of ponds go dry.

A lot of it has to do with the operator too though. Some thing they are just pushing soil into shape, but it is actually the tracks. Bulldozers have deeper grousers (treads on the tracks) that dig down deep and have wider spacings between them. By steering a lot, the lags work rocks and material tightly together like a jigsaw puzzle that allows the soil structure to stay together. This same logic applies to roads too. Today I see a lot of roads be built using excavators that simply knock the gravel flat, then it is compacted and maybe paved. But it does not stay that way for long though. You really need a bulldozer to do anything with putting in layers of fill material.