Region prepares to tackle stormwater runoff

SPRINGDALE — Leif Kindberg, executive director of the Illinois River Watershed Partnership, said he takes phone calls weekly from landowners in northwest Arkansas saying they are seeing stormwater on their land that they had never known before.

“Precipitation in northwest Arkansas is increasing significantly,” he said.

Kindberg shared numbers recorded at Lake Elmdale by the US Army Corps of Engineers. They said the average annual rainfall in Springdale increased by 10.5 inches between 2000 and 2021, he said.

National Weather Service data shows that 41.65 inches of rain fell in 2000 at National Airport in northwest Arkansas, according to the service’s website. The airport recorded 51.2 inches of rain in 2021.

“Climate change is happening,” agreed Ben Peters, director of Springdale’s engineering department. Peters became department head on August 1, replacing Brad Baldwin, who retired on August 20.

Elizabeth Bowen, project manager with the Northwest Arkansas Regional Planning Commission, said city and county leaders in the region want to develop a regional stormwater management plan.

“The plan will require both quantitative and qualitative stormwater drainage management,” Bowen said.

Kindberg cited the regional planning projection of one million people living in northwest Arkansas by 2045.

“Even with all the land, driveways, roofs and infrastructure that we see, half of what we will need in 23 years is not yet built.

“We have to get ahead and create a plan so that citizens can do their best,” he said.

The watershed partnership is currently reviewing its own stormwater management plan to identify sources of pollution carried by runoff into waterways in the Illinois River watershed. The plan will also consider using low-impact design features to mitigate runoff, such as riparian repair of stream banks or rain catchment systems for homeowners, Bowen noted.

And cities in the region may need to update their drainage requirements, she said.

“Developers meet minimum requirements,” Kindberg said. “But are the minimum criteria sufficient? What new levels do we have to meet stormwater flow?”

PEAK MANAGEMENT

Springdale does not allow more runoff from a property after development than before development, Peters said. However, the total volume of water flowing out could increase with the same amount leaving the property in a longer period of time, he said.

“We really manage the spikes,” he said. “Peaks that probably don’t occur in rivers and major streams, but more likely in small ditches and tributaries.”

The construction engineering industry has determined precipitation formulas for developers to determine the amounts of stormwater that require additional attenuation to remove, Peters said. These include rainfall data for the past 80 years.

“But like the stock market, history doesn’t dictate future events,” he noted.

Several different formulas are approved for determining runoff levels, but each measures differently, Peters said. The difference in peak rates could be statistically insignificant or off by about 25%, he said.

Every developer proposing a project in Springdale is required to submit the results of hydrological and hydrotic studies of the property and development to the city, Peters said. The department is currently working with about 80 or 85 ongoing development projects, he said.

Hydrology examines the distribution of water both on and below the Earth’s surface, as well as the impact of human activity on water availability and conditions. Hydrotics considers the sources of this water.

Peters explained that water flows out of the earth in two ways: concentrated and sheet. Concentrated flow flows in canals, ditches, streams – the most common flow for housing estates. Sheet flow is shallow water flow from a wide area. If sheet flow exists, developers should have a sheet flow study, Peters said.

The most common practice regionally and the national standard for stormwater disposal are retention ponds, Peters said. The ponds are most likely dry until rain fills them, and the water disappears within 24 to 48 hours, he said.

It is a retention basin that limits the volume of water leaving at any time. The size of the pipes in the pond’s drainage or weirs, which change the shape or speed of flowing water, make a difference, Peters said.

The city also offers a manual of low-impact design features that a developer can use to mitigate stormwater drainage. These can include rain barrels and stormwater catchment systems, which aren’t commonly used because they require more maintenance for homeowners, Peters said.

PONDS OR PAVERS?

Springdale developer Tom Lundstrum doesn’t like retention ponds. He said they take up space that could be put to better use.

The parking lot at Lundstrum’s Little Emma mixed-use development in downtown Springdale is made of permeable pavers, which allow water to drain into the ground, Lundstrum said.

“We only had 3/4 of an acre on this site and we needed the land instead of the pond,” he said.

Design and engineering processes are continuing for Lundstrum’s Big Emma project on East Emma Avenue, and stormwater drainage management plans have not been finalized, he said.

Land is still relatively cheap in northwest Arkansas, so developers generally don’t mind the pond taking up space, Peters said.

David Gilbert, an engineer with Plymouth Engineering in Lowell, noted that stormwater management must be unique for each site.

“Each site has different runoff patterns,” he said.

Gilbert recently worked with Scout Enterprises, developers of the proposed Hawksview subdivision on East Brown Road in the city’s northwest quadrant. Developers wanted to create a unique, low-impact community using older existing homes. These houses will be moved to the site and renovated inside and out.

The proponent proposed gravel road shoulders and gravel driveways, as well as rain catchment systems to reduce runoff.

The Planning Commission did not approve the plan, citing neighbors’ concerns about drainage. The June 14 city council overturned the commission’s decision and accepted the development for intended use.

TO REPAIR IT

Gilbert noted that he also worked with the city of Elm Springs to alleviate issues in the Camelot Subdivision. He noted that the subdivision was built before the city had any standards.

“In Elm Springs 10 years ago, their attitude was, ‘Build it, and we’ll fix it later,'” Peters said.

Even today, small towns don’t have engineering staff — unless the city hires one under contract, he said. Nobody reviews the drainage reports, he said.

Gilbert said a home builder filled in an existing drainage ditch and built a house across it.

“He didn’t take into account where it might flood,” Gilbert said. “It wouldn’t be built the same way today.”

Legendary, a subdivision immediately to the north, was abandoned by the developer amid the 2008 recession. That subdivision had no retention ponds, Gilbert said.

The water was falling towards Camelot.

Springdale has helped control flooding in Camelot, immediately west of Shaw Family Park, by building very large retention ponds in the park to control runoff, Gilbert said.

In another case, the city had authorized the construction of a one-story house, but in the middle of construction, the owner decided to add a basement without planning, Gilbert said. But that basement was lower than the property’s flood level.

“If it’s too low, it will flood,” he said.

“Flood issues are individual decisions,” Gilbert said. “You have to be careful what you do on each property.”

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