Big Mosquito Riparian Enhancement

Published January 18th, 2017 in Blog, What's Happening? | Comments Off on Big Mosquito Riparian Enhancement

Multiple large landslides within the Big Creek Subwatershed created meadows that historically functioned to store large volumes of water for gradual release later in the flow period. Thus, these meadows can extend the base flows into the drier summer months. Deadwood Creek reaches 1-3 is a depositional valley formed by the largest landslide within Big Creek and along with Big Creek reach 4 composes the core depositional features used for steelhead spawning within the Subwatershed. Deadwood reaches 1-3 have grass-dominated streambanks with alder communities that are being overtopped by lodgepole pine. These low gradient reaches have been drying out due to the absence of beaver. A lack of large woody debris or persisting beaver dams has resulted in channel incision. Fire suppression has led to an overly dense stand that created poor large wood recruitment and reduced biodiversity. The confluence of several tributaries with Big Creek is characterized by a steep gradient. Large wood is needed to control the grade and initiate pools within this section of the creek.

Wet meadows are becoming increasingly important water reservoirs. Increasing ambient air temperatures are predicted to cause both temporal and spatial changes in the delivery of fresh water. Scientists anticipate increased winter runoff from water melting earlier in the season and falling as rain rather than snow. This will cause earlier peak streamflows in the spring and diminshed runoff during the hot summer months. The outcome of these changes will be significantly altered flow regimes. Anadromous fish runs are adapted to typical flow conditions. The predicted changes in snowpack means that the John Day Basin will have to rely more heavily on other forms of natural water storage. Wet meadows collect and store runoff, which not only helps prevent seasonal flooding, but also ensures the availability of water throughout the dry summer months.

Unfortunately, the hydrologic function of several meadows within the Big Creek-Middle Fork John Day Watershed has been impaired by the presence of gullies and incised channels which transport water off the meadow. The result is a dry, dusty meadow with a decreased water table and reduced riparian vegetative biomass and biodiversity.

For this project, the Malheur National Forest chose to use the natural resources available rather than bring in man-made materials. Large Woody Debris (LWD) was placed in the streams to concentrate scour, store sediment, and promote the creation and maintenance of quality pools. The LWD placement consisted of 80-100 large trees (diameter at least 12 inches) per mile and 438 small trees (diameter between 4-12 inches) per mile. Twenty percent of the large trees were greater than 20 inches in diameter, at least 35 ft long, or 1.5 times the bank-full width of the stream.

This project pioneered a new strategy for wet meadow restoration. Healthy wet meadows act as nature’s sponges by soaking up available water, storing it, and slowly releasing it during the dry season. However, the meadows in this project had been drained by gullies and incised channels which conveyed the water off the meadow much faster. For this project, trees and brush were cut and placed in the incised channels to decrease the flow of water running off the meadows. The North Fork John Day Watershed Council provided five youth crews to perform the task of installing the woody material into gullies of each of the six identified meadows.In one meadow, the benefit of the work was visible within only a few days. As the meadow began to rehydrate, the wet area increased in distance from the filled channel.  

Funding for this project was provided by the Malheur National Forest and The Oregon Watershed Enhancement Board


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