ABSTRACT

Replanting riparian vegetation can improve ecological health but there are few guidelines that help stakeholders achieve shade targets cost-effectively. A computer model was extended to calculate average shade to direct and diffuse solar radiation in straight channels. It was used to recommend strategies for achieving shade targets, including the 70% guideline shown to prevent nuisance aquatic plant growths and extreme water temperatures. For similar trees on both banks, 70% shade occurs when the ratio of tree height (H) to stream width (W) lies in the range 1.0 < H/W < 2.6 depending on stream orientation and tree shape (canopy overhang and dripline height). With trees on both banks, shade is lower by up to 34% in east–west (EW) than north–south (NS) streams except for tall trees at the equinox. EW streams planted only on the north bank can have a 30% higher shade than NS streams planted on one bank, but low vegetation on the unplanted bank eliminates this difference. For EW streams in the Southern hemisphere, planting tall vegetation on the north bank is cost-effective, with low vegetation on the south bank providing additional benefits. Further work is planned on channel meandering, gaps between trees and canopy transmission.

摘要

重新种植河岸植被可以改善生态健康，但很少有指导方针可以帮助利益相关者经济高效地实现遮荫目标。扩展计算机模型以计算直通道中直接和漫射太阳辐射的平均阴影。它被用来推荐实现遮荫目标的策略，包括所示的 70% 指南，以防止滋扰水生植物生长和极端水温。对于两岸的类似树木，当树高 (H) 与溪流宽度 (W) 的比率在 1.0 < H/W < 2.6 范围内时，会出现 70% 的遮荫，具体取决于溪流方向和树形（树冠悬垂和滴水线高度） ). 两岸都有树木，东西向 (EW) 的树荫比南北向 (NS) 溪流低 34%，除了春分时的高大树木。仅种植在北岸的 EW 溪流的遮荫度比种植在单岸的 NS 溪流高 30%，但未种植的河岸上的低植被消除了这种差异。对于南半球的 EW 溪流，在北岸种植高大植被具有成本效益，在南岸种植低矮植被可提供额外的好处。计划在通道蜿蜒、树木之间的间隙和树冠传输方面进一步开展工作。