Water flowing off 500 acres into Crestview Ditch during storms threatened to flood homes until a city construction project this summer rectified things.
Over the years, water carved vertical drops in the dirt ditch, one nearly 18-feet deep, and left neighboring fences hanging in mid-air, said Keith Dougherty, a civil engineer with the city.
“This channel has been a long-standing problem,” he said.
The ditch is one of the projects identified for work in the city’s stormwater master plan from the 1980s.
This year, the city budgeted $100,000 to update the master plan to re-evaluate its drainage needs. An update is needed because added development leads to more paving, and that creates more sources of runoff. Also, the city must meet new federal and state requirements, said City Manager Ron LeBlanc.
The need for better drainage has been demonstrated – during major rainstorms in the last few years, water has hit homes and inundated streets, including areas near 32nd Street, College Drive and East Eighth Avenue, and 15th Street and Rotary Park.
“The climate is changing. What we’re seeing recently is more intense events,” he said.
The potential for flooding at the Riverbridge Apartments helped the ditch project qualify for a federal grant, Dougherty said.
Construction on a concrete culvert and pipes started in April, and it is expected to wrap up in about four weeks, he said.
The ditch spans about 150 feet down the hillside between Avenida del Sol and Roosa Avenue. It is designed to handle 300 cubic feet per second, the equivalent of what the city would expect to see in a 100-year flood event, he said.
The project is expected to cost about $1.26 million. The Federal Emergency Management Agency will cover 75 percent of the project. The city will pay about $359,000.
The project qualified for federal money as a form of disaster-mitigation. It is cheaper to address flooding issues before they happen, Dougherty said.
Crews started construction at the bottom of the ditch and built what looks like an empty concrete pond to help slow the water. This piece of mitigation required 88 cubic yards of concrete – the load of about 10 concrete trucks.
Water flows from the pool via a box culvert and makes its way underneath Roosa Avenue near the Durango Skate Park to the Animas River. The new drainage ditch will help keep water flowing into the Animas River cleaner, but dirt and sand will continue to flow through the ditch.
Above the pond-like structure, crews put in rock terraces and seeded the hillside to help hold the soil in place.
A box culvert and two aligned pipes, one 5 feet across and the other 6 feet across, lead to the retention area.
“There is about 30 feet of vertical drop we are trying to fix,” he said.
The pipes, which will be buried 8 feet deep, will create a more gentle slope to help slow the water. This will allow neighbors to walk on top of the drainage area to tend their yards, Dougherty said.
The new master plan, which may be finished in 2017, will outline other drainage projects needed in the city.
Funding for those projects is uncertain. They could be paid for with current revenue streams or the city would need to look for new sources, LaBlanc said.
“If there is an overwhelming number, we would have to go back to the council and look at the best practices that other cities follow,” he said.
mshinn@durangoherald.com
