SKUNK RIVER PIPELINE PROTECTION PROJECT NEAR DENMARK, IOWA SUB MAR

Skunk River Lee & Des Moines County, Iowa ANR Pipeline Company SUB MAR Looking US at Bendway Weirs and stable bank, flat slope depositional areas are an excellent indicator of stability.

Before Installation Skunk River Lee & Des Moines County, Iowa ANR Pipeline Company SUB MAR Pre-project: Looking US from the area where the pipeline was exposed by river forces

Before Installation Skunk River Lee & Des Moines County, Iowa Pre-Project: Looking US. The river was eroding the right descending bank, becoming over-widened, and eroding a top-bank farm levee. WE ARE GOING 1,000 FT OFF OF THE PIPELINE RIGHT-OF-WAY FOR A LONG-TERM SOLUTION.

Skunk River Lee & Des Moines County, Iowa ANR Pipeline Company SUB MAR Looking US at Bendway Weirs and stable bank, flat slope depositional areas are an excellent indicator of stability. Flow

Skunk River Lee & Des Moines County, Iowa ANR Pipeline Company SUB MAR Looking US at Bendway Weirs and stable bank, flat slope depositional areas are an excellent indicator of stability. 2 Hard Points 9 Bendway Weirs LPSTP & ACM Flow

Skunk River Lee & Des Moines County, Iowa ANR Pipeline Company SUB MAR Looking US at Bendway Weirs and stable bank, flat slope depositional areas are an excellent indicator of stability. LPSTP Bendway Weirs, LPSTP & ACM Flow

Skunk River Lee & Des Moines County, Iowa ANR Pipeline Company SUB MAR Looking US at Bendway Weirs and stable bank, flat slope depositional areas are an excellent indicator of stability.

Looking DS at the ACM protection after the first flood, note erosion immediately US of the mats

Construction of Bendway Weirs, Hard Points, & LPSTP occurred in October 2001 SUB MAR

Well-graded stone, but few fines, for Skunk River project, Denmark, IA. To effectively use this stone we installed a granular filter of 1 to 3 inch stone, then installed this stone.

Key trench for Bendway Weir #9. Granular filter (1 to 3 inch stone) is installed, then overtopped with key stone.

Skunk River, Denmark, Iowa. Looking upstream. Keying into, and connecting the US Bendway Weir with the DS Articulated Concrete Mattress pipe cover protection using a section of Longitudinal Peaked Stone Toe Protection, (LPSTP, about 1.5 tons/ft.)

Looking DS at the completed LPSTP tie-in

Looking DS after 2 yrs, at ACM protection over a formerly exposed gas pipeline Note: Pipeline was exposed at the toe of both banks, meaning the river had degraded (system- wide bed lowering) and overwidened (CEM Type III).

A system of Bendway Weirs, seen here in a physical movable- bed model, flow is left to right

UNREVETTED BEND REVETTED BEND Newly installed Bendway Weir Effects of Bendway Weir

Within the weir field 2.6 ft/sec Thalweg 6.4 ft/sec 8.0 ft/sec Looking DS at flow over a series of Bendway Weirs, high water on Catt Creek & Savage Rd., NY 11/4/2004

Skunk River Lee & Des Moines County, Iowa ANR Pipeline Company SUB MAR Looking US at Bendway Weirs and stable bank, flat slope depositional areas are an excellent indicator of stability.

Looking US at Bendway Weir #9 on the Skunk River, 8 more Bendway Weirs up-river plus 2 Hard Points US of that, protecting 1,400 ft of bankline.

Looking US during high water, ACM mat placed to cover exposed sections of pipeline, flood has occurred since installation, weirs not in yet. Note eroded US bank.

Looking US. Sediment is being trapped by weirs. Banks are stabilized, vegetated (a good sign) with the bank building (deposition, not retreating).

Looking BW & stable bank. Note LPSTP in foreground

Skunk River Lee & Des Moines County, Iowa ANR Pipeline Company SUB MAR Looking US at Bendway Weirs and stable bank, flat slope depositional areas are an excellent indicator of stability.

Skunk River, looking US from pipeline crossing, two years after installation

Skunk River – Mats Lee & Des Moines County, Iowa Submar Drawing No. AB643 2 Years After Installation 1 Year After Installation After Installation 1 Year After Installation Before Installation SUB MAR ANR Pipeline Company

Looking DS at Bendway Weirs and ACM, Skunk River, Denmark, Iowa Keys for Bendway Weirs Submar Mats SUB MAR ANR Pipeline Company Bendway Weir Post-project thalweg location Pre-project thalweg location

This last flood we had (July 2008) was pretty severe and flooded the fields on both sides of the river at the site. After the water receded a few feet and the levee was visible again, it appeared to be undamaged. Also from what I could see from the opposite side of the river (I couldn't get very close), the vegetation was undisturbed on the river side of the levee and there were no signs of erosion. The thalweg looked to be following the line of the ends of the weirs and the water close to the bank was moving very slow comparatively. And this was with a water level several feet above the tops of the weirs (about five feet from the top of the levee) nice! Nick Beach, Construction Manager, Submar SUB MAR

The End

Three pipelines are covered with ACM mats in the river, seen here at low water stage. Upstream of the right-of-way bendway weirs were installed in the bend. The water is just over the top of the weirs in this photo. ANR Pipeline Company Skunk River Lee & Des Moines County, Iowa Point Bar Flow Redirected Flow Uncontrolled Flow Captured Flow Bendway Weirs Bendway weirs are a proven technology developed & used by the U. S. Army Corps of Engineers. Bendway weirs have been used in large rivers such as the Mississippi River & in small streams. Demonstration projects in small streams have found that in addition to stabilizing the outside of a bendway, weirs have provided improved fish habitat (quantity and diversity) to the stream. Constructed Oct 2001