Weather Forecast


Scott Rall: We can get many benefits from a hole in the ground

SUBMITTED PHOTO A look over the recently completed retention pond located on the Minnesota West community college property shows experimental floating islands installed by the Okabena Ocheda Watershed.

Scott Rall

WORTHINGTON — The what, where and why of large manmade holes in the ground is a pretty interesting topic.

The depressions that I am referring to can be seen more and more often as property is developed around local communities and even in the farm landscapes of ag country in southwest Minnesota.

A drive around Worthington will allow you to see two of them across the road from Olson Park. A drive out to the new 59/60 highway a few blocks from Shine Brothers has two really big ones, and even a saunter down First Avenue Southwest and you can see one on the church property.

These manmade holes or depressions are called storm water retention ponds, or sedimentation ponds, depending on what they were designed for. The newest one in town is a very large retention pond that was constructed on the property owned by Minnesota West Community and Technical College. It is one really big hole in the ground, and as a result of its construction the fill needed to construct the bike path was close and readily available.

One of the sure-fire ways to know and identify what you might be seeing is to look for the three-foot tall orange cone with large holes in it standing all by itself in the middle of a dry patch of ground. A retention pond’s primary purpose is to collect surface water runoff that results from rain or snow-melt events.

It contains the surge of water within its margins and then metes it out slowly in the direction that it normally travels. So a big rain will be held temporarily and then be dispersed over a period of 24-48 hours or even longer. By holding the water temporarily and releasing it slowly, flooding is reduced. The bigger the retention capabilities, the more water can be retained on the landscape and the more flooding can be prevented.

If the precipitation event or melt is so large that the pond fills to overflowing, the water then exists at the rate it would as if the structure did not exist. If the pond exists in an urban setting, it is most likely a retention pond. It catches the water that runs off impervious surfaces, and in addition to slowing the water down it also acts as a pollution catch. Water that can carry with it chemicals from streets, parking lots, commercial properties and the like can be held for a period long enough for some of those contaminants to settle out before making their way downstream into public waters like the lake or streams that provide drinking water for humans.

A sedimentation pond does much the same thing but has an additional purpose of catching sediment that carries with it phosphorus. Phosphorus is the chemical most loved by algae. It is the cause of the stinky algae blooms that most of our area lakes suffer from starting about this time every year. This chemical, for the most part, is not moved in water alone. It is attached to the smallest particle of sediment, and it is the movement of this sediment to the lake that carries most of with the phosphorus.

If you stop this movement of sediment/phosphorus enough, you can eventually see cleaner water and less algae blooms. This is something everyone wants.

Another large sedimentation pond was constructed by the Okabena-Ocheda Watershed just west of the municipal golf course. It has been credited with a substantial reduction in sediment and resulting phosphorus movement to Lake Okabena.

The college pond provides all of the above benefits. It catches the runoff from the college properties’ impervious surfaces, but also receives and contains runoff water from a large number of agricultural acres west of town.

It is certainly a multi-purpose big hole in the ground. When I visited with the college supervisor in charge of this project, Gordy Heitkamp, three years ago, he shared with me the projected cost of this effort. I was very supportive, but thought there was no way in the world that they could raise the kind of funds necessary to get it done.

The project got a shot in the arm from the college and then received funding from the watershed and the E.O. Olson Trust Fund, but it was still a long way from becoming a reality.

When the rest of the parties involved came to understand the benefits of this water improvement project, everything fell into place, and today the pond is a reality. I commend those with the foresight that helped make this project a reality. This type of planning is now part of all future development in almost every town across America. Water resources are a finite commodity, and the protection of those resources has gotten a much higher level of attention in the past decade.

Many retention ponds hold some water year round (one to three feet deep), and others go dry in the summer months. Depending on their location, they can offer limited wildlife value. Others, like the college pond that holds enough water year-round, have the ability to provide fishing opportunities, and the college is working in that direction.

The plan is to stock this pond with appropriate species of fish and provide additional recreational opportunities in addition to the water quality improvements that it will certainly provide.

Please do not get the hare-brained idea that you are going do a midnight stocking of your own. It will only guarantee that the formal efforts of others will not be successful. The efforts expended and hundreds of thousands of dollars spent to create the local retention and sedimentation ponds are not all that needs to be done. These are done primarily in urban settings, but with the total acreage of towns only accounting for 1 percent of the land mass, sediments need to stay where they are on all the acres of Minnesota.

This goal can be advanced by making sure that there are grassed waterways in farm fields everywhere they are needed. In addition to grass waterways grass buffer setbacks, (60 feet of grass on each side of the stream) also slow the water and allow the sediments to be collected in these buffer areas, thus staying on the land instead of making it to the fast moving streams.

Unfortunately, many of these water protections that have been in place for decades are being plowed under and instead yield more rows of corn or beans directly adjacent to important water resources.

In order to protect our limited water resources, it is going to take everyone involved to do their part. One or two or even 10 expensive retention ponds here or there is not enough to catch all the water and the sediment that is carried in it.

Everyone needs to do more, but this project is one shining example of one that is done right. Take a drive past the college and look at this project. Thank the college for their leadership and for leading by example. In the end all game, fish and wildlife will benefit from clean, unpolluted water.