A Research On The Hydrological Comparability Of The Cai Jia Chuan Basin Based On The Topographic Index

The hydrological scale problem is an advanced and difficult issue in hydrological fundamental researches. The interrelation is very close between the hydrological scale and the hydrological similarity. If we can find some similarity, we may treat the hydrological scale problem by the similarity. In the paper we study the hydrological similarity between the Cai Jia Chuan basin and her son basins in order to support researches on the scaling between the Cai Jia Chuan basin and her son basins.We study the hydrological similarity between the Cai Jia Chuan basin and her son basins by analyzing the similarity of the topographic index frequency distributions between them according to the principle that if the topographic index frequency distributions of two basins are similar the two basins are of the hydrological similarity in condition that their underlying surfaces is supposed to be same. We must calculate their topographic indices in order to get their topographic index frequency distributions. To calculate topographic index need use some arithmetic based on the digital elevation model. Consequently, the key is to choose a fitting resolution of the digital model and a proper arithmetic for the paper.We simulate the digital elevation models of different resolutions about the research area with the soft wares Photoshop 7.0 and TNT MIPS 6.9 in the topographic map of the Cai Jia Chuan basin on the scale of one to ten thousand. We write programs based on the single flow direction and the multiple flow direction arithmetic for calculating the topographic index with the IDE Visual Basic 6.0. We calculate the topographic index of the research area with the programs on the digital elevation models of the different resolutions. We get the topographic index frequency distributions after treating the results with the soft ware Excel. By analyzing the topographic indices and the topographic index frequency distribution of the different resolutions and different arithmetic we think that the 50 meter resolution and the multiple flow direction arithmetic are fit to the study on the hydrological similarity between the basin and her son basins.We extract the digital elevation models of the son basins from the digital elevation model of the basin with soft ware TNT MIPS 6.9 and calculate their topographic indices with the multiple-flow -direction arithmetic program on the digital elevation models. We get their topographic index frequency distributions after treating the results with the soft ware Excel. By analyzing the similarity of the topographic index frequency distribution between the basin and her son basins, we find the number four and the number five and the number seven basin are similar to the Cai Jia Chuan basin.