International Dredging Review

International Dredging Review

Newt Marine Services of Dubuque Iowa is in the second year of a three-year project to create wildlife habitat in the Upper Mississippi River in Harpers Slough.

The project is in Harpers Slough at approximately RM 650 to 653+ opposite Lynxville Wisconsin. For 2016 Newt’s dredge River Walker is pumping sand to restore and create four is-lands having created three islands in summer of 2015. 


The Harpers Slough project map shows the river bend at RM 650 to 653+ the two in-channel dredged material borrow areas and the features that comprise the project including islands backwater channels backwater habitat areas and rock sills.

The River Walker is a 20-inch Ellicott 1270 cutterhead dredge. 

This year islands M5 L6 W1 and W3 are being constructed along with rock sills W1 and W2.

In 2015 Newt Marine restored three islands — M5 L1 and L3 — bringing them to project elevation and capping with two to three feet of mud. It also built rock mound M8 and dredged access channels A10 and A6 using the dredged material to cap the islands. 

The overall project involves creating and restoring seven islands and creating extensive backwater habitat including deepwater areas for fish to over-winter. The three islands created last year will be planted with willows and other native plants this spring and the islands created this year will be planted in spring of 2017.

This summer’s work plan also includes the construction of two rock sills to protect the new islands.  


On board the 20-inch dredge River Walker which has pulled over to allow a commercial tug to pass.

The islands are long and narrow each a half mile to a mile long and approximately 170 feet wide. This year’s work will require more than 228000 cubic yards of sand more than 60000 cubic yards of topsoil fines and more than 44000 tons of stone. 

“The wildlife uses the islands as fast as we can make them” Arnold said. As soon as land appears the area is surrounded with pelicans gulls ducks and other animals he said.

The dredge is working inside the channel in two places to acquire sand for the islands with pipeline lengths from 5000 to 10000 feet de-pending on how far the fill area is from the borrow area. The dredge moves over to allow commercial vessels to pass in the narrow shipping channel. All pipeline is outside the channel and the dredge cables are on the bottom and don’t interfere with passing vessels Newt Project Manager Dan Arnold explained. 


Rock Sill W1 is partially complete on May 2.  Its purpose is to protect the island struc-ture from erosion and to provide habitat for the wild creatures that use the area. The rock is removed from the barges and placed with a backhoe. Rock Sill W1 will be approximately 600 feet long with a 10 foot wide top width taking approximately 6500 tons of riprap stone to construct.

“The U.S. Coast Guard provides a notice to mariners to alert commercial traffic to our location.  We have buoys and markers on and around our dredge and equipment along with night lights to alert traffic to our presence.  Commercial traffic passes our work area without interference or slowing” Arnold said.

The island bases are established with sand from the shipping channel then capped with two to three feet of mud dredged from the backwater channels and other habitat areas. These deep areas will provide over-wintering habitat for fish. Rock sills are strategically located to protect the island structures from erosion and to provide habitat for the wild creatures that use the area Arnold said. 

Arnold explained that mud for the wetland structures is pumped in using the hydraulic dredge.  For the cap on the islands the mud is loaded into barges by an excavator moved to the island and loaded onto haul trucks for transportation to the capping location. 

“After that mud is carefully graded using a bulldozer” he said.


Pelicans gather on a newly-created island in Harpers Slough on May 2 2016.  Birds flocked to the islands as soon as they appeared above the water line Proj-ect Manager Dan Arnold said.

Rock is brought from a local Iowa quarry by barge and placed using a backhoe. 

During the winter workers collected young willow trees and kept them in cold storage to be planted on the islands this spring along with grasses and other native plants. They will assemble willows and other plants this winter to plant on this year’s islands next spring. 

This project is a part of the Upper Mississippi River Restoration Program which was established in 1986. The Corps of Engineers has restored more than 45000 acres or 62 square miles of river and floodplain habitat within the St. Paul District under the plan.