Road lateral disconnection and crossing impacts in river landscape of Lancang River Valley in Yunnan Province, China

Roads are conspicuous components in a river landscape; however, their impacts on river landscape patterns and ecological processes have not been systematically studied at the watershed scale. In this paper, the Lancang River Valley in Yunnan Province, China was selected as a case to study road lateral disconnection and crossing impacts and identify river-road network interaction. This study was primarily focused on the road impacts on soil erosion intensity and patch density by using GIS analysis at different scales and explored their distribution with terrain factors. The results showed that river density revealed spatial autocorrelation although both of the roads and rivers were distributed unevenly in the valley. The lateral road (road curvature ≥ 1.1) proportion correlated with soil erosion intensity (p ≤ 0.01) at the small sub-basin scale. Soil erosion intensity decreased with increasing lateral road buffer width. Light erosion generally accounted for a large proportion of the erosion in the lateral road buffer zones (1.0–4.0 km), while higher class lateral roads imposed greater impacts on soil erosion than lower class roads, which primarily had a moderate erosion level. In addition, the results of road-river intersection density indicated that road crossing impacts were significantly correlated with patch density at the small sub-basin scale. Topography factor (percent of slope > 25° in each sub-basin had a close relationship with the ratio of total length of road line with curvature value ≥ 1.1 to the total number of intersections. The correlation (p ≤ 0.01) between road impacts and terrain factor revealed that topography affected the road impact distribution in the Lancang River Valley.