New culvert spans salmon spawning creek

MAT-SU - The Department of Transportation & Public Facilities (DOT/PF) is not only concerned with the mobility of humans in Alaska, but of all animal species. The installation of the new multiple-use pathway along the Palmer-Wasilla Highway runs perpendicular to fragile salmon spawning grounds in Wasilla Creek. Working under guidelines from a document called the Fish Habitat Permit, administered by the Alaska Department of Fish & Game (ADF&G), DOT/PF carefully worked around the spawning site.

Spawning in Wasilla Creek for chinook and coho salmon began in mid-July and continues through the fall. The salmon eggs are extremely vulnerable to any type of disturbance like pressure, shock or the introduction of suffocating sediment. The anadromous creek also supports resident Dolly Varden and rainbow trout. ADF&G authorized work in the stream for a 2-month window from May 15 to July 15.

A request was granted by ADF&G for the work window to extend an additional three days through July 18.

Engineers determined that the new 10-foot wide pathway on the north side of the highway required more ground area than was available.

To accomplish this, workers extended the tops of the existing culverts by 14 feet and dirt was placed on top.

An 85-foot long monolithic concrete head wall was poured around the culverts to support the increase in mass, replacing a smaller supporting wall. Warm weather and a lack of rain helped ease construction, said Project Engineer Bill Klebesadel, because the creek water level stayed low.

Incredible measures have been taken to reduce impact on the stream, said Klebesadel. The permit provided very realistic guidelines to work within.

In order to isolate the stream from construction efforts, workers placed a 55-foot reinforced-plastic liner along the north side of the stream bed to act as a funnel, constraining water as it flowed into a temporary 5-foot-wide culvert. Any water that seeped out into the construction site was sent through a silt-removing filtration system before it was allowed to join the larger liquid flow.

Vehicles were not allowed to operate in the creek, and silt fences were erected to prevent sediment-laden runoff from entering the water.

One of the major goals was to minimize damage to the vegetation, Klebesadel said.

Workers from Fike Brothers Building, Koch Construction, and Cruz Construction were diligent in protecting the surrounding plant material, according to Klebesadel.

Replanting and hydroseeding will take place to protect against erosion before the end of July. They will also place massive stones called riprap on the bottom of the creek to build an unerodable stream bed.

The Fish Habitat Permit was administered by the ADF&Gs Habitat and Restoration Division on July 29, 1998. Construction efforts were expected to last a few more days than originally planned, so an extension was requested by DOT/PF.

Authorization for the extension was given under the conditional term that DOT/PF permanently block the illegal ford through Wasilla Creek on the south side of the highway. The ford was used frequently by all-terrain vehicles and subsequently disrupted salmon migration and rearing waters.

Photo: The rebar skeleton for the concrete head wall can be seen around the newly-extended culverts. The reinforced liner that was used to contain Wasilla Creek can be seen in the background the temporary culvert that it flowed into had to be of a diameter that did not increase the water velocity to a point where fish would not be able to swim upstream, Bill Klebesadel, right, said.

Photo by ZACHARY ZIBRAT.