Dam removal leads to sediment issue for Edmonson Water District (USA)
Author: isi网站管理员-刘成Source: Updated: 2017-07-10

By JACKSON FRENCH, jfrench@bgdailynews.com (Jul 8, 2017)

The removal of Lock and Dam No. 6 on the Green River outside Brownsville is having unintended consequences for the Edmonson County Water District.

Tony Sanders, manager of the water district, said the utility needs to move its water intake screens, located downstream, to avoid a buildup of sediment that has grown more severe since the dam, which was built in 1904, failed in November.

“In the hundred years, there’s been sediment building up behind it,” he said. “Now that the dam has come out, that sediment is migrating downstream.”

Moving the intake screens up 2 feet is expected to clear up the problem because it would remove them from the part of the river where the flow of sediment is heaviest.

“Typically the silt migrates along the bottom of rivers,” he said.

The buildup of sediment could potentially hinder or altogether stop the water district’s ability to collect water, Sanders said.

“It can stop all our flow entirely,” he said.

Since November, the district has had to hire an outside firm to clear away the sediment buildup on the intake screens twice, something that only needed to be done about once every 10 years before, according to Tim Brewster, a spokesman for the district.

Raising the intake screens would probably cost the district $15,000 to $16,000, he said.

Mike Turner, an ecologist with the U.S. Army Corps of Engineers, which monitors the dam, said a scour hole that formed under the dam is causing water to flow faster through part of the river, with much of the sediment being swept away in this quicker stream.

“The sediment’s going to go where the fastest, most energetic water goes,” he said.

The Corps of Engineers’ efforts to remove the lock and dam and fill in the scour hole with parts of the lock and dam in March and April have not been completed because the hole is larger than initially expected, Turner said.

http://bloximages.chicago2.vip.townnews.com/bgdailynews.com/content/tncms/assets/v3/bannerad/e/86/e86378e4-8dc0-11e3-83e6-001a4bcf887a/52f1266be6140.image.jpg

“We just ran into a much bigger hole than we were expecting,” he said.

Until Thursday, the raising of the intake screens was scheduled for this Saturday and Sunday, as well as July 13-14, Sanders said. Shortly after learning of the Nature Conservancy’s interest in running some tests on the area and filling in the scour hole completely, the district decided to wait until afterward to see if moving the screens was still necessary.

Michael Hensley, with the Nature Conservancy, said the Conservancy wants to run tests of the sediment in the river and perform an analysis of Lock and Dam No. 5, which, despite being 14 miles downstream, could have an impact on the water district’s intake with a drop in the water level if the dam fails or is removed.

“Lock and Dam No. 5 creates a pool and (the pool) does extend up as far as the Edmonson water intake,” he said.

Hensley also said the Conservancy plans to finish filling the scour hole, which would be a joint project with the Corps of Engineers.

He said filling the scour hole would greatly reduce the amount of sediment flowing directly into the path of the intake screens and may spare them the cost of raising the screens.

Filling the scour hole requires a low water level, something that’s been difficult to come by because of the region’s rainy weather lately, meaning when the process of filling the hole would begin or end is unclear, he said.

(Source: http://www.bgdailynews.com/)

Produced By CMS 网站群内容管理系统 publishdate:2018/07/03 10:22:32