Correspondence James C. Bathurst, School of Engineering, Cassie Building, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK. Email: james.bathurst@ncl.ac.uk Abstract The extent to which forests, relative to shorter vegetation, mitigate flood peak discharges remains controversial and relatively poorly researched, with only a few significant field studies. Considering the effect purely of change of vegetation cover, peak flow magnitude comparisons for paired catchments have suggested that forests do not mitigate large floods, whereas flood frequency comparisons have shown that forests mitigate frequencies over all magnitudes of flood. This study investigates the apparent inconsistency using field-based evidence from four contrasting field programmes at scales of 0.34–3.1 km. Repeated patterns are identified that provide strong evidence of real effects with physical explanations. Magnitude and frequency comparisons are both relevant to the impact of forests on peak discharges but address different questions. Both can show a convergence of response between forested and grassland/logged states at the highest recorded flows but the associated return periods may be quite variable and are subject to estimation uncertainty. For low to moderate events, the forested catchments have a lower peak magnitude for a given frequency than the grassland/logged catchments. Depending on antecedent soil saturation, a given storm may nevertheless generate peak discharges of the same magnitude for both catchment states but these peaks will have different return periods. The effect purely of change in vegetation cover may be modified by additional forestry interventions, such as road networks and drainage ditches which, by effectively increasing the drainage density, may increase peak flows for all event magnitudes. For all the sites, forest cover substantially reduces annual runoff.

中文翻译：

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森林和洪水：使用现场证据协调分析方法

通讯 James C. Bathurst，工程学院，纽卡斯尔大学 Cassie Building，泰恩河畔纽卡斯尔，NE1 7RU，英国。电子邮件：james.bathurst@ncl.ac.uk 摘要 相对于较短的植被，森林在多大程度上缓解了洪峰流量仍然存在争议，而且研究相对较少，只有少数重要的实地研究。考虑纯粹的植被覆盖变化的影响，成对集水区的峰值流量大小比较表明，森林不能减轻大洪水，而洪水频率比较表明，森林可以减轻所有洪水量级的频率。本研究使用来自 0.34-3.1 公里尺度的四个对比性实地计划的实地证据来调查明显的不一致。重复的模式被识别出来，这些模式通过物理解释提供了真实效果的有力证据。幅度和频率比较都与森林对峰值流量的影响有关，但解决了不同的问题。两者都可以显示在最高记录流量下森林和草地/伐木状态之间的响应趋同，但相关的重现期可能变化很大，并受估计不确定性的影响。对于低到中等事件，森林集水区在给定频率下的峰值幅度低于草地/伐木集水区。根据先前的土壤饱和度，给定的风暴可能会在两个流域状态产生相同量级的峰值流量，但这些峰值将具有不同的重现期。纯粹植被覆盖变化的影响可能会通过额外的林业干预措施来改变，例如道路网络和排水沟，通过有效增加排水密度，可能会增加所有事件强度的峰值流量。对于所有地点，森林覆盖大大减少了年径流。