Last week I discussed using precision conservation as a method to aid in planning flood control systems. I strongly feel we can do a better job placing ponds to reduce flooding. It used to be a time consuming job, but in the past few years new tools have been introduced to assist in completing this analysis, and subsequent designs. The following is a case study written in December 2013 highlighting some practical applications of PondBuilder in Iowa.
High Praise for PondBuilder
By Lynn Betts
Dave Rohlf likes to have all the information he needs at his fingertips when he designs a pond. His boss, Gabe Lee, at the Iowa Department of Natural Resources likes the fast, accurate design products Dave delivers at a low cost to the Department. Both men appreciate the time savings and consistency that come with PondBuilder, the computer program Dave has used for two years to design sediment basins that protect state lakes the DNR manages and the public enjoys.
“These sediment basins are essentially the same as ponds,” Rohlf says. “They’ll trap 95 percent of the sediment that would otherwise enter a lake. PondBuilder gives me all the tools I need to gather data I use to make good decisions on their size and location.”
Rohlf worked 32 years with the USDA Natural Resources Conservation Service, serving as both the State Design Engineer and Assistant State Conservation Engineer during his career. He says if he didn’t have PondBuilder available, he would be using planimeters and counting dots by hand over drainage areas on maps like he did 30 years ago. “Those methods are fine for design—they work. But they take 4 to 5 times longer than it takes me to design with PondBuilder,” he says.
“As far as I know, the engineers and other conservationists are going to several sources to get data on drainage areas, runoff curve numbers and other information. With PondBuilder, I’ve got all that in one package,” he says, “with the exception of a routing program. I use Winpond. It’s not inside PondBuilder at this time, but it’s the only extra step I take as I use PondBuilder for design.”
Rohlf has designed between 15 and 20 of the structures to protect Red Haw Lake near Chariton in Lucas County and Hawthorne Lake in Mahaska County. Three of the structures have been built around Hawthorne Lake and 6 are under construction around Red Haw Lake. “It’s taken up to 3 hours to design a structure using LiDAR and PondBuilder, compared to probably a couple of days with the older methods to survey and design a structure,” Rohlf says.
The program uses LiDAR (light detection and ranging) elevation data for design and layout. There’s no survey at all. “These structures are in some really steep, nasty gullies that are difficult and very time-consuming to survey,” he explains. Instead, the work is all done at Rohlf’s computer at his desk at DNR. “The DNR hires me on an hourly basis as a part-time employee to do this design,” Rohlf says. “It’s been a big savings for the DNR—their engineering department loves it.”
“The DNR identifies the drainage area and gully where each pond will be built,” Rohlf says. “Then it’s up to me to locate the pond in that gully. I look at the aerial photos and pick the best centerline I see in PondBuilder. I’m looking for a structure that will store the optimum sediment for 100 years, considering cost of construction. If the first site works for storage and costs, that’s great. But if it doesn’t, it’s very easy and fast to move the centerline up or down the gully slope and consider an alternative. It doesn’t take long to do that with PondBuilder. It’s so fast, you haven’t lost much time when you start over. But it would take a long time if you were starting over and surveying it like we used to do.”
Speed and accuracy
That speed doesn’t come at a cost of less accuracy, Rohlf says. In fact, he’s convinced PondBuilder is as accurate as anything else he’s used. “It’s probably more accurate,” he says, “and I’m not so sure it isn’t as accurate as GPS. You may need to be a little more careful with layout, to match LiDAR with points on the ground. But you have to realize with the older methods there are judgments and estimates—hydrology is estimated, ten-year rainfall changes, and there are other areas for possible inaccuracies. It’s how you use the data that matters, and PondBuilder does that very consistently.”
Looking back, Rohlf says the program would have been useful earlier in his career. “Almost any of the small structures could have been designed with PondBuilder. They all use the same data. The numbers in the program are all better with PondBuilder. Drainage area, runoff curve number, and time of concentration are all more accurate than I can get with any other method available to me,” Rohlf says.
Rohlf has done enough design work in his conservation career to recognize solid designs. “I’m very comfortable with the results I get from this program. The old methods of design are fine, but we can do it better and faster with PondBuilder,” Rohlf says. “It’s been good for me. I love it.”
To get conservation on the ground, we have to work faster and smarter. Continuing to use the same basic methods with small tweaks to the process and with a shrinking workforce focusing on conservation is a losing proposition. PondBuilder is a paradigm shift, not a tweak to the process.
To see an example of a PondBuilder report, go to https://www.agrentools.com/wp-content/uploads/2014/11/PondBuilderPlannersReport1.pdf.
See more about Agren’s precision conservation software at www.agrentools.com.