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- Storm water drainage problems persist in Nephi City Storm water drainage problems persist in Nephi City
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By Myrna Trauntvein
Times-News Correspondent
Nephi continues to have storm water drainage problems during high volume rain storms.
Mayor Mark Jones asked Randy McKnight, city administrator, to review with the city council the storm water drainage master plan that was recently prepared and discussed the recommendations from that plan.
The council also discussed some of the storm water drainage issues that are apparent when storm water runoff is present at various locations in the city.
"On the west side of the city there is a little slough or stream," said McKnight. "The Old Hollow used to grain into that stream when there was high water."
That flow to West Creek has been interrupted by homes that have been built where once there were open fields. As the land becomes more developed, he said, more problems with storm water drainage occur.
Another problem that has developed came because of the construction of the Interstate 15 on the east side of the community. Culverts were placed under the freeway to allow water from the mountains to the east of the city to pass into the city.
Flood control for the city was part of the study done for the city storm water drainage master plan.
Some of the points identified, he said, are that city growth has used up farm ground and covered the land with parking lots, homes, streets, sidewalks and has generated more storm water flow because the water from east of the city once spread out and percolated into the land.
"There is a lack of drainage after storm water crosses Main Street," said McKnight.
East of the city, where the water used to spread out, it now comes through the I-15 culverts and aims for houses.
"We are also dealing with collapsible soils," he said. "That limits how we deal with storm water."
The city also lacks adequate funding to address many of the drainage issues. There is not enough money in the general fund, for one thing, to address the problems that need to be taken care of.
"There are 16 drainage basins," said McKnight.
These are geographical areas that affect the amount of water that ends up in the city.
"Nine of those are mountain drainage areas," he said.
As that storm water comes through the city it now tends to concentrate into certain areas rather than allowing "sheet" flows.
One of the largest drainage areas is the Salt Creek Drainage which collects water from 95 square miles and drains into Salt Creek. There are two types of floods that generate from this area.
Much of the problem from that drainage occurs in the spring of the year when the snow melts. The other type comes from heavy rainfall or thunderstorms.
Ninety-five percent of the time the area is arid.
There are catch basins built in Miller and Biglow Canyons to prevent flooding of the city that traditionally flooded the south part of the city whenever there was a lot of snow melt or whenever there was a cloud burst.
Gardner Creek is a stream located just 2.6 miles east of Nephi and comes out just above Nephi on the south.
In addition to Miller Canyon and Biglow Canyon, there is Red Canyon, Quaking Aspen Canyon, and Old Pinery Canyon which all drain toward the city, east to west.
Since the city has expanded to the south, the Old Pinery Canyon has created more drainage problems.
Biglow Canyon leads to a detention basin but any overflow comes into South Town subdivision, after coming under the freeway, as the water tries to head west.
Storm drainage problems are increased because of impervious soils. Those two issues have created challenging drainage problems for that area of town.
"We get many calls from people throughout the community who tell us that, 'It didn't used to back up here but now it does,'" he said.
Engineers working on the plan for the city did work to break the community up into different drainage basins. For example, the drainage of various areas were broken into acres of the drainage leading to certain areas of the city.
By comparison, Gardner Canyon with 44 acres and Quaking Aspen Canyon with 1,662 acres pale in comparison with Salt Creek Drainage which is made up of 60,000 acres.
"The engineers created a hydraulic model," said McKnight.
After the storm water comes into Nephi from Salt Creek drainage, it can be separated as it travels through the city into Salt Creek and into Old Hollow.
The study also looks at structures which may help move water and others which may impede the flow, discusses the size of a storm that can be moved, and talks about the 100-year storm.
"During the floods of 1984 and 1985, we did not reach the level of a 100 year storm," said McKnight.
Of importance to city council members, is the capacity of structures.
"Some bridges on the east side of the city can handle 900 cubic feet per second," he said. "That goes down to only 700 cubic feet per second further along the storm drainage but still on the east side of the community."
On the west side of the city, that capacity is even more diminished.
The railroad tracks, west of the city, are an obstruction to storm water flow.
"We ought to start now to plan how to get water to West Creek before the city grows more," said McKnight.
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