Loomis Creek Eco-hydrology Phase 1 Study: 2024-2025

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 (m²) and mobile bedload grainsize (cm) with increasing upstream drainage area (km²). 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.

加拿大公园与荒野协会（Canadian Parks and Wilderness Society, CPAWS）对海伍德河上游流域内一项新近获批的皆伐伐木计划开展了生态水文野外评估。此前，阿尔伯塔省林业与公园部门针对该伐木计划开展了一项基于桌面研究的水文评估与部分风险分析，结果显示该伐木活动将使年均径流量与峰值径流量分别提升约10%，并引发更早、更迅猛的春季融雪洪水。该分析建议针对当前河道形态、河岸带状况、干扰历史，以及公牛鳟（Salvelinus confluentus）关键栖息地的脆弱性开展野外调查。CPAWS完成了此项调查，以论证在溪流与河岸带被法定列为关键栖息地的流域中，所需开展的详细评估程度。调查发现，该计划规划的道路、跨河设施与皆伐区域，距离流域内公牛鳟产卵、鱼卵越冬孵化以及幼鱼育幼的最敏感关键栖息地，最近仅10米的上坡与上游距离。伐木活动将直接破坏或损毁关键栖息地，且该计划未完全遵循省级作业基本规则（Operating Ground Rules, OGRs）以及联邦《濒危物种法》（Species at Risk Act, SARA）的恢复策略要求。本次野外评估首次证实，卢米斯溪存在一处被浮木壅积带与海伍德河隔离开的定居型公牛鳟种群。该溪流上游与下游河段坡度较陡，该种群高度依赖（若并非完全依赖）唯一一处具有完整冲积河道形态的河段。该河段位于卢米斯溪中游，坡度相对平缓，也是唯一观测到公牛鳟产卵以及当年幼鱼（young of the year, YOY）育幼的区域。该栖息地质量优异：低速水流蜿蜒流经由可移动砾石组成的河床，横跨宽阔的河狸草甸漫滩；其深潭-浅滩型河道形态包含回流、分流汊道、牛轭湖以及河狸塘。对径流量、电导率与水温的测量结果显示，此处存在冲积地下水补给。在36个调查点位中，林线以上子流域面积与主导坡向的变化，呈现出随上游汇水面积（km²）增加，河道横截面积（m²）与移动底沙粒径（cm）均增大的趋势。皆伐区域的积雪量更大、融雪更快，将进一步提升年均径流量与峰值径流量，并引发更早、更迅猛的春季融雪洪水。历史伐木影响的支流已出现河岸侵蚀、河道下切、底沙输移以及河道淤积与退化的迹象，而本次规划的皆伐区域面积远大于历史伐木，因此其水文影响将更为显著。卢米斯溪中游河段风险最高：在新伐木活动引发水文改变之前，当前径流条件下其底沙已完全可移动。当高流量水流截断河道蜿蜒段且产卵砾石被冲刷至下游时，关键栖息地很可能会遭到破坏。卢米斯溪流域此前的野火与历史伐木并未对水文响应最为敏感的上游源头区域造成影响，但本次规划的皆伐区域多集中分布于南坡，将产生此类影响。此前的桌面水文评估显示，森林的水文恢复过程十分缓慢；卢米斯溪及其支流因径流量提升而造成的关键栖息地丧失，可能会使公牛鳟的产卵与育幼活动减少甚至中断长达50年及以上，这将威胁卢米斯溪公牛鳟种群的存续。