Mat River erosion-control plans discussed

BOB MARTINSON/Frontiersman reporter

PALMER - A plan to move gravel out of the Matanuska River via conveyor to a gravel pit on the Glenn Highway was one of the options discussed in a meeting Wednesday about proposed erosion-control techniques for the river.

About 65 people showed up at the Atrium building in Palmer to listen to results of a federal Natural Resources Conservation Service feasibility study that tested computer models on proposed erosion-control methods for the river, which, in the past, has eaten away parts of the Circle View subdivision.

Rob Sampson, a state conservation engineer for NRCS, used a slide show, aerial photographs and geographical charts to present different river-control scenarios.

The meeting's goal was to better inform the community about the ever-changing river, as more and more residents are getting involved in problems associated with it.

"I'm just glad to see so many people getting concerned about this problem and getting involved, showing up for this meeting," said Linda Smith, of the Circle View and Stampede Estates flood and water erosion control service area. Circle View subdivision's erosion problem was alleviated by some hastily installed spur dikes that deflected the river but are now in need of repair. The dikes change the flow of other parts of the river,and residents at the meeting expressed concerns over what each proposed plan could do to other parts of the river, including upriver changes that occur from manipulation of the river's natural flow.

Dennis Nottingham of PND Inc., an engineering company contracted by the borough to provide river-control measures, presented an idea that is meant to slow the river and give royalties from the sales of river-extracted gravel to the borough, helping with long-term maintenance costs of the plan.

Nottingham's plan involves dredging a large pit in an area downriver from the Circle View subdivision to catch large amounts of gravel, and for that gravel to be extracted or harvested using a long conveyor that would move the material across the dry north fork of the Matanuska River, past the Sky Ranch subdivision and into the existing Wilder Construction gravel pit on the Glenn Highway.

This idea has alarmed residents of the Sky Ranch area. The conveyor, they say, would mar the view of Pioneer Peak they enjoy from homes that carry the highest property tax bills in the Valley. Noise and lights associated with the proposal are also concerns.

Sampson presented graphs depicting riverbank dollar-per-foot costs for the proposed measures on each of the river-control ideas, including the "do-nothing" plan.

The braided river moves about a half-million tons of gravel per year, Sampson said, and most of the material is of a very small caliber, which moves easily.

Getting federal funding for such projects is difficult and the Palmer Soil and Water Conservation District - an organization run by a local board elected from agricultural producers - helped involve NRCS with the studies to help document the problems.

Sampson described how spur dikes increase the velocity of the current at the tip of each dike, causing faster sediment transport and other problems. The dikes draw in the current behind them.

He said digging trenches down the river helps the water flow and protects the river bank, but that these trenches would be difficult to maintain and require an annual upkeep dredge, if permits could constantly be acquired for such measures.

"We found that wherever there are trenches, the riverbank is protected and wherever they are not, there's constant erosion, but it's hard to maintain trenches," Sampson said. "You can't dig during salmon migration and the seasonal limitations makes it hard to do it."

Covering banks with Rip Rap, a protective coating of large rock, increases velocity and is also problematic, as the rock that originally gets dumped into the river piles in at the trench and then the water meets it, causing more turbulence and other flow problems.

Existing spurs or dikes installed by Nottingham for the borough, to save the Circle View subdivision, didn't work as they were supposed to. Sampson and others at the meeting said they are failing - they had been constructed in a hurry, because there were apparently not enough large rocks available at the time to construct spurs out of the materials necessary to sustain the spur-dikes over time.

The proposal involving the gravel-extraction scenario is apparently under way.

"Nottingham and PND has provided us with an action plan and we plan to implement it soon, but it won't happen for at least a year or so," said Borough Manager John Duffy, after he was contacted at his office Thursday. "We are working on an integral mining district ordinance pertaining to gravel mining that will provide guidelines to consider concerns and to alleviate any negative impacts. We don't want to create any nuisances. Maybe we can run the conveyor at only certain times of day or something."

PND's plan contains the following recommendations:

€ Obtain necessary permits and complete major maintenance of the existing spur dikes, and extend spur dike #3.

€ Obtain necessary permits and construct a new spur dike.

€ Construct an excavation area south of the existing spur dikes.

€ Complete a geotechnical exploration of the proposed excavation site.

€ Obtain the state's approval to excavate and sell the gravel.

€ Determine conditions for gravel-extraction proposals and prepare and issue a request-for-proposal for a private firm to mine and purchase the gravel.

€ Award gravel excavation contract and initiate extraction.

"The immediate plan of action, our first order of business, is to get out in early spring and get those dikes taken care of," Duffy said.

At the end of the meeting, Rob Sampson said, "We've now gotten you concerned people together with this study, so you can possibly get together and come to some kind of consensus, so you can hopefully, someday, spend other people's money."

People who want more information may contact the Palmer Soil and Water Conservation District at 745-1441, Rob Sampson at (907) 272-2424 or Linda Smith of the Circle View subdivision board, at 745-8475. Nottingham's company, PND, can be reached at www.pndengineers.com or (907) 561-1011.