Matanuska River erosion fight funded

MAT-SU -- The Matanuska-Susitna Borough has received a $100,000 grant from the federal government to start work on environmental studies and a plan for dredging, to prevent the Matanuska River from further eroding its banks and use the dredged material as a gravel source.

The federal grant came as part of the fiscal year 2002 energy and water appropriations bill passed at the end of October.

"The problem with that river is that it carries so much material," said Mat-Su Borough Public Works Director Jim Swing.

That's also pointed out in correspondence that borough lobbyist Steve Silvers used to present the borough's case in Washington, D.C.

"A tremendous amount of material has been deposited near Palmer in the middle of the river course," the borough's presentation materials say, "This makes the erosion even more severe as the deposited gravel forces the river to move to the shoreline where even more land is eroded away."

Borough officials also wrote that "several" homes had been destroyed.

According to Swing, the environmental and planning work would be in preparation for a project that is estimated to cost $2 million.

"The idea is not necessarily to get the river to stay in one channel, but to get it to stay in manmade channels," Swing said. It's not known at this time how many channels might be necessary, according to Swing.

Engineer Dennis Nottingham of Anchorage-based Peratrovich, Nottingham, and Drage designed finger dikes (also known as spur dikes) in the early '90s to prevent erosion along the river. Nottingham said he has also looked into dredging channels -- called incised channels -- into the mile-wide river bed to provide a more predictable flow.

"It's a river channel that has definite banks and the water flows

beneath the banks," Nottingham said of the incised channels. Nottingham said similar projects had taken place at Lemon Creek near Juneau, and at Fourth of July Creek and the Resurrection River near Seward. Nottingham believes the Matanuska could be held inside dredged incised channels permanently, provided the channels were maintained.

"I suspect it would just be a sustained thing," Nottingham said. "Anchorage needs a very definite gravel supply -- they use hundreds of thousand of yards a year." Nottingham also pointed out that existing gravel transportation infrastructure, such as conveyors and the railroad, take gravel to the Anchorage market.

"You already have all of the ingredients," he said.

Nottingham, who designed the borough's Port MacKenzie dock, said he couldn't predict if the river gravel would be valuable enough to pay dredging costs, or even marketable. But, Nottingham said, the plan is worth studying, even if it doesn't prove viable.

"If not, then it just becomes something you tried," he said.