4.3 The utilization potential of alluvial fans
The distances between alluvial fans and road, human settlement and water system are important factors effecting the utilization potential of alluvial fans. The transport network density of Tibet is lowest among all the provinces of China (Jin et al., 2010), which indicates that transport roads are sparse in LRB. However, the quantity percentage of alluvial fans distanced to primary road and tertiary road not more than 5 km are 79.51% and 99.72% (Fig.10), so the most of alluvial fans are easy to access. LRB has a typical semi-arid frigid climate (Lin et al., 2008), so water resource is an important factor for regional development. The quantity percentage of alluvial fans distanced to river not more than 5km reach 61.86% in this semi-arid basin (Fig.12). It’s showed the majority of alluvial fans will be appropriate for agricultural or residential development from the water perspective. There is a situation should be focused that some rivers located between roads and alluvial fans. For the utilization, those rivers have two functions, of providing water resource and cutting the accessibility to alluvial fans in this situation. In order to adequately use those alluvial fans, some bridges could be built in the future.
The area of grassland and bare land in alluvial fans is 802.59 km2, and the area of alluvial fans which is occupied by grassland not less than 50% (A50%grassland) even reach to 903.17 km². The land-use degree of grassland and bare land is lower than cropland and imperious area (Zhuang & Liu, 1997). So those two types of alluvial fans, A50%grassland and A50%grassland A30%bare land, should be more utilization potential based on reasonable explorations. Besides, the utilization potential of the alluvial fans located in the west and south of LRB should be focused. There are many A50%grassland (Fig.8), and near rivers in the west (Fig.1). Therefore, alluvial fans in Damshung may be more protentional in the future. The Chenguan is an urban area of Lhasa city which is capital of Tibet located in the south of LRB. And the government residences of Tolung Dechen, Chushur and Taktse are near with Chenguan. Therefore, the south of LRB especially near Chenguan should be more needed for available land than another region. There are alluvial fans with 243 km²in the region, meanwhile some bare land are located in those alluvial fans. So, the alluvial fans in this part may be utilized adequately the future.