Changing the mountain environment

bolstering the mountain road environment. road protection and landscape management should be combined to reinforce one another.

CHANGING THE MOUNTAIN ENVIRONMENT

The development of a road unavoidably changes the environment of mountain areas, including the hydrology, microclimate, and sedimentation patterns. The changes in hydrology affect several dimensions. first, the development of a road changes surface runoff patterns. rather than flowing down a smooth gradient, the runoff is interrupted once or several times while descending from the newly cut hillside. The flow velocity is reduced as the runoff touches the road surface and erosive force is released. as the runoff touches the road surface it may concentrate and accumulate along the road surface, effectively changing the natural drainage pattern. Second, in a similar fashion, subsurface flows are interrupted in road construction. The degree to which water travels in the upper soil layers and geological formations differs from place to place and from road section to road section. roads disrupt these shallow moisture flows and, in many areas, cause new springs and seeps to emerge. a third effect on hydrology is that opening a road cut in hilly terrain also opens fresh mountainsides and increases the air-surface exposure of the hill slope (photos 6.2 and 6.3), which will dry out the hill slopes, particularly when the slopes are freshly cut. Moreover, a gully effect occurs, with soil moisture moving toward the road cut, where it constantly evaporates. Unless the side

PHOTO 6.2

Increased air-surface exposure of hill slope

Source: © MetaMeta (www.roadsforwater.com). Used with the permission of MetaMeta (www.roadsforwater.com). Further permission required for reuse.

PHOTO 6.3

Interrupted subsurface flow caused by road openings along Mugu Humla Road, West Nepal

Source: © MetaMeta (www.roadsforwater.com). Used with the permission of MetaMeta (www.roadsforwater.com). Further permission required for reuse.

slope is covered again with vegetation, it may lead to “bleeding” of the subsurface moisture, drying up hillsides. fourth, the construction of roads will also increase the so-called hydrological connectivity of the watershed. Hydrological connectivity describes the degree to which hydrological elements of a landscape are interconnected. The higher the connectivity, the faster the rainfall runoff, causing peak flows in the rivers to emerge early and be more pronounced (Meng, Wu, and allan 2013). Chapter 2 further describes this phenomenon. road development generally accelerates runoff, making new connections and concentrating flows in a smaller number of drainage lines. furthermore, the opening of roads in steep mountain terrain exerts a large impact on the microclimate (see figure 6.1) of roadside areas. This impact can be observed, for instance, when forest areas are traversed. The impact on the microclimate is caused by the changed hydrology and the greater exposure of the mountain slopes to sun and wind and reduced tree canopy once roads open up the roadside environment. The general effect will be for the area surrounding the mountain road to dry. Such drier road environments and reduced soil moisture affect soil temperatures (more heat exposure) and microbiology. When soils are less moist, microbial action in the soil decreases, which will, for instance, reduce the capacity to fix nitrogen, with repercussions for vegetative growth. Gradual drying, an increase in daytime temperature, and a lowering of night