The Boulders at Long Flat
Creating A Wild Trout Nursery. In 2010 thirty boulders were installed on the riverbed of the Erikson/Naumer property at Long Flat on the East Branch to help establish a wild trout nursery. In addition, Trout Refuge Structures and bank ledge overhangs were installed in 2011 and 2012. The goal of this work was to establish a "Nursery" for trout fingerlings and yearlings in the riffle and run water they prefer to inhabit. Just as a Nurse will protect their charges, so these habitat improvements will protect young trout. And as this is a prime area for Mergansers and older adult trout to feed on them, a more complex aquatic habitat with refuge areas should allow for more retention of these young trout, enabling a healthier fishery with more adult trout, and thereby more spawners.
Construction. The boulders were initially delivered and stored on an upland area of the property, then transported down to the riverbank on the day of the installation. A pair of boulders were placed just off the bank in the riverbed, and then one of the two excavators employed was stationed on top of these boulders, allowing it to place the next boulders as close to the center of the river as possible. This excavator then removed one scoop load of gravel from the riverbed where each boulder was to be dropped. A second excavator was used to hand the stored boulders to the excavator on the riverbank. The first excavator would then place a boulder in the shallow pit it has just created, and then a second boulder would be placed against it, just upstream, creating a pair. This second boulder, depending on the height of the stream, would then break the water's surface. After the first pair was placed, the escalator operator would then be instructed on placement of the remaining boulders in order to create a cluster of three pairs. We placed a total of five such clusters, each placed in a way to direct water from one pair to the next, and also in such a way to create some faster or deeper water between and/or just downstream of each cluster.
After all the prime boulders were placed in the main channel of the river, left over boulders were placed either just off the bank, or on the bank in the upstream section of the work. The upstream bank placement allowed us to better stabilize the river bank against high flood waters. The placement of boulders just off the bank allowed for a richer aquatic environment close to the bank, where many fingerlings like to hold, and also allowed us to create a Winter holding area for young trout as well. We accomplished this by placing many smaller 4" to 12" boulders against the larger boulders, which provided the interstitial space these young trout prefer to hold in during the winter months. Once this work was done, we placed large bluestone slabs on the river bank to provide overhanging ledges for small trout cover. Finally, our last effort was to provide gravel on the riverbed near the bank, placed where we believe it may be stable as well as stay relatively free from cobbling. If well placed, we may be able to create a spawning bed for upcoming years. As a whole, this work of course tremendously increased the complexity of the aquatic environment in the riffle and run at the head of Long Flat.
Boulder Retention. The boulders were placed on the riverbed when the stream flow was at its annual low, about 80 cfs. Within a week, a storm came thru raising the flow to 8,000 cfs. The following year saw a 20 year flood with flows of 20,000 cfs. One of the boulders placed near the bank moved slightly, offsetting from its previous position perhaps 6-12 inches. Otherwise none of the boulders moved. This does not mean we won't have some movement in future floods, but we appear to have created a complex aquatic environment with some stability to it.