DOI: 10.6084/m9.figshare.29173691
title: Loomis Creek Eco-hydrology Phase 1 Study: 2024-2025

description: Canadian Parks and Wilderness Society (CPAWS) conducted an eco-hydrological field assessment of a recently approved clearcut logging plan in the upper Highwood River watershed. An earlier desktop-based hydrologic assessment and partial risk analysis of the same logging plan conducted for Alberta Forestry and Parks found the logging will increase mean annual and peak flows by approximately 10% and result in earlier, more rapid spring freshets. It recommended a field investigation of current channel morphology, riparian conditions, disturbance history, and vulnerability of bull trout (<i>Salvelinus confluentus</i>) critical habitat. CPAWS did this to demonstrate the level of detailed assessment required in watersheds where streams and riparian areas are legally designated as critical habitat.Planned roads, water crossings, and clearcuts were found within as little as 10 m upslope and upstream of the most sensitive critical habitat in the watershed where bull trout spawn, eggs incubate over the winter, and juveniles rear. Logging will directly damage or destroy critical habitat, and the plan does not follow all the requirements of the provincial Operating Ground Rules (OGRs) or the federal <i>Species at Risk Act</i> (SARA) recovery strategy.The field assessment confirmed for the first time that Loomis Creek is occupied by a resident bull trout population that is isolated from the Highwood River by log jams. With steeper stream gradients in the headwaters and lower reaches, the population relies heavily (if not entirely) on the only reach with a fully alluvial channel morphology. This mid reach of Loomis Creek where the stream gradient is lower was the only reach where bull trout spawning and young of the year (YOY) rearing were observed. Habitat quality is high because low-velocity flows meander through a broad beaver meadow floodplain over a stream bed of mobile gravel. The riffle-pool channel morphology contains back eddies, side channels, oxbows, and beaver ponds. Measurements of stream flow, electrical conductivity, and temperature suggest there is an influx of alluvial groundwater here.At 36 sites surveyed, the size of the subwatershed area above tree line and the predominant slope aspect are reflected in trends of increasing channel cross-sectional area (m<sup>2</sup>) and mobile bedload grainsize (cm) with increasing upstream drainage area (km<sup>2</sup>). Heavier snowpacks and more rapid snow melt in clearcut areas will increase mean annual and peak flows and result in earlier, more rapid freshets. Existing signs of bank erosion, incisement, bedload movement, and channel aggregation and degradation on tributaries effected by historical logging indicate that the effects from the planned logging will be even greater due to a much larger area being clearcut. The mid reach of Loomis Creek is most at risk, with a bedload that is already entirely mobile under the current flow regime before any hydrologic alteration from new logging occurs. Loss of critical habitat is likely where stream meanders are cutoff in high flows and spawning gravel is swept downstream.Historical wildfire and logging in the Loomis Creek watershed did not affect the most hydrologically reactive headwaters, but the planned clearcuts, disproportionately on south facing slopes, will. The earlier desktop-based hydrologic assessment showed hydrologic recovery of the forest has been slow, and loss of critical habitat due to higher flows on Loomis Creek and its tributaries could reduce or stop bull trout spawning and rearing for 50 years or more. This threatens the sustainability of the Loomis Creek bull trout population.