Upper Trout Brook Observations - Dr. Doug Thompson
Dr. Doug Thompson on upper Trout Brook.
Trout Brook Observations/ASSESSMENT
Trout Brook upstream of Channing's Pond shows little sign of sediment mobilization with low density organic material in the main channel, moss covered rocks and rocks greater than approximately 10 cm (4 in) in diameter characterized by angular shapes showing little fluvial rounding and abrasion. The brook has little evidence of floodplain development showing little lateral migration. The system appears to be very stable both vertically and horizontally, with a very muted flood response. More dynamic sediment movement is likely to reduce some of the embeddedness that has occurred, which should improve macroinvertebrate populations and brook trout spawning habitat.
The lack of evidence for any flashiness in the hydrograph is likely related to several multiple artificial impoundments upstream of Channings Pond that would attenuate any flood peaks and the undersized rock culverts under the railroad right-of-way. These impoundments created near stagnant flow at the moderate flow observed on June 26, 2023. Large volumes of organic material were observed deposited in the small impoundments investigated, as well as Channings Pond.
Temperature measurements collected on the date suggest that a newly discovered low small artificial impoundment upstream of the railroad track increased water temperature relative to just upstream of the impoundment by 3 degrees F on June 26. The combination of the earthen berm and concrete impoundment just downstream had a similar but notably worse impact and increased temperatures by roughly 15 degrees on the same day. Temperatures in the concrete pool did decrease relative to water impounded upstream of the earthen embankment, but temperatures from directly below the railroad crossing to below the concrete impoundment still show a dramatic warming trend.
There is also a strong likelihood that the impoundments above and below the railway are strongly impacting dissolved oxygen (DO) levels in the brook. Decay of the organic debris (probably mostly leaf matter) will suck much of the oxygen from the water in the impoundments, making those areas problematic for fish survival. The turbulent areas downstream of these areas help dissolved oxygen levels rebound to some degree. The oxygen reducing conditions in the impoundments is also likely to impact pH levels to some yet to be determined degree.
With regard to next steps, I have included a link to some Massachusetts LiDAR DEM data (https://www.arcgis.com/apps/mapviewer/index.html?webmap=1a85cbb55637464b9d03e0b1dc5cb13e). This DEM can be used to better understand the longitudinal profile of Trout Brook to see how removal of the 3 small upper impoundments could reduce backwater impacts on the channel. It was noted on the DEM that there is a second tributary to Trout Brook upstream of the concrete impoundment that flows from the southwest towards the northeast and originates to the west of Miller Hill Road. The temperature impact of this tributary should be investigated. This tributary also appears to have an additional small impoundment that should be investigated. It is also worth looking at dissolved oxygen and pH levels along upper Trout Brook and its tributaries, especially immediately upstream from, within, and downstream of impoundments.
As an overall preliminary recommendation, removal of the 3 small impoundments is likely to improve water quality and temperature conditions along upper Trout Brook. Removal of the impoundments (upstream of the railroad bed and the concrete impoundment/earthen berm) is likely to improve temperature, DO and pH conditions along the channel and will also likely improve the ability of the channel to rework some of the bed material to a small degree. Because of the existence of the large Channings Pond impoundment downstream, it is unlikely that any change in flood attenuation will be observed downstream of Channings Pond.
Dough Thompson and NFC ED Bob Mallard assessing piped earthen berm.