Study On Characteristics Of Urban Rivers And Agricultural Ditches In Lake Dianchi Basin

Spatial and network features of rivers and ditches in Lake Dianchi Basin were analyzed by geographic information system technology. Agricultural ditches were derived from Quickbird images of January 6, 2008 and March 11, 2007. Urban rivers were sketched from 1:50000 Lake Dianchi Basin base map of 2008 and Kunming city map of 1980. The results indicated that:1. The riparian vegetated bands of urban rivers were too narrow to control pollutants. The range of the vegetated bands is 3m to 20m. The riparian vegetated bands of natural rivers outside downtown area is 9m to 41m. The range of the curvature ratio of urban rivers was 1.07 to 1.42 in study area. The urban rivers had a low curvature ratio except of Baoxiang river, comparing to the rivers of outside downtown area which were greater than 1.2. The connectivity of urban rivers was 0.43 and the circuitry was 0.14 in study area. The urban rivers inside the second urban circle(main urban district)had a low connectivity and circuitry, which was 0.35 and 0.03. In past 30 years, the density of urban rivers reduced in three fold.2. The agricultural ditch system included trunk canal, branch canal and lateral canal, which were made by concrete or block stones. And terminal canals were soil-beded. Lateral canal structure determined the width of vegeted buffering zones, 0m to 1.1m of which were made by concrete or block stones. and 0.9m to 1.6m of traditional one with soil-beded. The Agricultural ditches of Lake Dianchi Basin had similar network characteristics. The range of connectivity is 0.41 to 0.44 in four sample sites, and circuitry is 0.12 to 0.16. There were denser ditch network on eastern bank. And the fractal dimension index of ditch networks were larger on southeastern and southern banks.3. Three study areas were selected in south bank area for optimal design, The connectivity and circuitry were increased in demonstration plots. Three-dimensional structure of agricultural ditches were optimized to play a better role in environmental function.