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）针对海伍德河上游流域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局针对同一伐木计划开展的桌面式水文评估与部分风险分析曾指出，该伐木活动将使年平均流量与峰值流量提升约10%，并引发更早且更迅猛的春汛。该分析建议开展野外调查，以评估当前河道形态、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。CPAWS开展此次评估，旨在论证当溪流与河岸带被法定列为关键栖息地时，流域内所需开展的详细评估深度。
调查发现，该计划中的规划道路、涉水构筑物与皆伐区域，距离流域内最敏感的公牛鳟关键栖息地的上坡与上游距离仅不足10米——该区域正是公牛鳟产卵、鱼卵越冬孵化与幼鱼育幼的场所。此次伐木活动将直接破坏或摧毁关键栖息地，且该计划未完全遵循省级作业基本规程（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，卢米斯溪内存在一处定居型公牛鳟种群，该种群因原木堆积障与海伍德河隔绝。由于上游源头区与下游河段的河道坡度更陡，该种群高度依赖（即便不是完全依赖）流域内唯一一处具有完整冲积河道形态的河段。该河段为卢米斯溪中游，河道坡度相对较低，也是唯一观测到公牛鳟产卵以及当年生幼鱼（young of the year, YOY）育幼的区域。该区域栖息地质量优异，缓流在宽阔的河狸草甸泛滥平原间蜿蜒流动，河床由可移动砾石构成；深潭-浅滩型河道形态包含回流、支汊、牛轭湖与河狸塘。对溪流流量、电导率与水温的监测显示，该区域存在冲积地下水补给。
本次共调查了36个点位，上游林线以上子流域面积与主导坡向的变化，呈现出随上游集水面积（km²）增加，河道横截面积（m²）与可移动床沙粒径（cm）均随之增大的趋势。皆伐区域的积雪更厚、融雪更快，将进一步推高年平均流量与峰值流量，引发更早且更迅猛的春汛。历史伐木活动影响的支流已出现岸坡侵蚀、河道下切、床沙输移以及河道淤积与退化的迹象，而此次计划的皆伐面积远大于历史伐木，因此其影响将更为严重。卢米斯溪中游河段面临的风险最高，在新伐木活动引发水文情势改变之前，当前水流情势下其床沙已完全处于可移动状态。当高流量引发河道裁弯取直、产卵砾石床被冲刷至下游时，该区域的关键栖息地很可能丧失。
卢米斯溪流域内的历史野火与伐木活动并未对水文响应敏感的源头区造成影响，但此次计划的皆伐区域集中分布于南向坡地，将对该区域构成威胁。此前的桌面式水文评估显示，森林的水文恢复进程十分缓慢；卢米斯溪及其支流因流量升高导致的关键栖息地丧失，可能使公牛鳟的产卵与育幼活动减少甚至中断长达50年及更久，这将对卢米斯溪公牛鳟种群的存续构成威胁。