I attended the 10th annual storm water tour on September 20, 2018. Most of the people on the bus were professionals in the field, either civil engineers or industry reps. Here are my photos from the tour.
The first stop was the parking lot outside Baxter Arena, where they attempted to use islands to catch runoff. They have learned not to use cobbles at curb cuts because the water going around them excavates the dirt. Instead, make a sump to catch sediment. Use a dome grate rather than a flat one so as not to clog it with mulch. Then "plant the snot out of" any exposed soil, with rhizomatous grasses.
The next stop was the retention basins at Hitchcock Park. A city official spoke about the Combined Sewer Overflow project which has been rebranded Clean Solutions for Omaha (keeping the same acronym). It will cost $2 billion to separate the combined sewers by 2037. In many cases adding dedicated storm water tunnels is not possible due to existing infrastructure, so the approach has been to divert water to catchment areas where it can infiltrate into the ground. The 3 basins at Hitchcock Park manage 26 acres of runoff along 42nd St. They are required to drain in 24 hours to prevent pests; a valve can be opened if they don't drain fast enough, but so far that has not been necessary. The basins are planted with flood-tolerant grasses through a standard open-weave landscape geotextile. Stormwater is pretreated by sumps to catch debris and sediment.
Papio Valley Nursery grows all the rain garden plants for the city's retention basins, specializing in sedges (Carex spp.). They are good for erosion, weed control, nutrient capture, and also aesthetics. There is a sedge for every microclimate!
We then went to the bioretention bed at the UNO Welcome Center. It was planted initially with dwarf species, but they crossbred with natives and got leggy. Buffalo grass only does well in full sun. As in Hitchcock Park, drains were installed under the bed, but the valves have been closed from day one. Webcams and sensors in the bed stream data to omahastormwater.org.
Albright Park retention basin had a big bang for the buck, because there was only one storm drain serving the entire cul-de-sac. It also collects a lot of sediment from highway runoff.
Our final stop was in Council Bluffs, where a whole neighborhood near Lake Manawa has been paved in porous asphalt. The service has to be vacuumed a few times a year to remove sediment clogging the pores. Water still drains to the lake, but now it's filtered by infiltration. We also visited a sewage pump station utilizing a vacuum pump, since the sewer lines are below lake level. Each house has a vacuum pit with a pressure valve.