Study Of Runoff Generation And Concentration Of The Typical Watershed On The Loess

Human activity has great effect on runoff yield and concentration for basins. Because of the special human activity on the Loess Plateau, the Yellow River's runoff is decreasing from 1960's. In this paper, Chabagou watershed (typical watershed on the Loess Plateau)'s runoff change from 1960's to 1990's was analysed. With the help of hydrology models on the nature condition and land surface changed condition, the change of rainfall and the human activity's effect on hydrology modeling is measured in this paper.For the complex land surface condition, the relationship of rainfall and runoff is very anomaly. Runoff is hard to be modeled by uniform experience formula. And what's more, when the land surface condition changed, the experience formula lost its validity. Based on distributed hydrologic model, grid-based lag-and-storage method and dynamic runoff generation and concentration method, which considering the effect of human activity on each grid, are in detail shown taking Chabagou watershed as an example. The digital terrain parameters are extracted from DEM(digital elevation model) which resolution is 950m × 950m. The location of dams and reservoirs et al are distributed on the grids by considering their real location on the watershed. The model also used the mix-runoff-yield method which considering the variation of runoff-yield area. The modeling results show the feasibility of this method. Model using the gird-based lag-and-storage method and dynamic runoff generation and concentration method considered the land change on grid-scale and reflect the condition of every periods, so it would make reasonable response to rainfall. Bringing the effect of human activity on runoff into the distributed hydrologic model, the nature law of watershed and the effect of human activity on runoff are deeper understood.Many parameters of the distributed hydrologic model are extracted from DEM. Change in DEM space resolution and sampling method will have great impact on hydrology modeling. In this paper the effect of DEM resolution on drainage properties extracting is examined for a study basin using DEM of increasing grid size. The result shows that watershed characteristics extracted from different DEM data resolution may be statistically different. We statistically analyses the watershed character values such as elevation, gradient, length of watershed network, topographic index, watershed area, stream density and mainstream length. The mean, various, maximal valueand minimal value of some of the objects are analysed in detail. Coarser the resolution is, more smooth the terrain is. Average gradient and length of watershed network and stream density minish with decreasing DEM resolution. Topographic index increases with DEM resolution. The concept of entropy has been considered a promising method in this study as it quantitatively measures the information produced by an object (watershed). With the DEM grid size increasing, entropy become smaller and smaller; and entropy of average resample is larger than center resample one's. DEM with various resolutions are obtained from two methods: average resample and center resample. The result also shows that average gradient of average resample is smaller than center resample one's; but the length of watershed network and stream density is on the other way round. This means the conflux time of average resample may be longer than center resample one's. And mainstream length of average resample is more close to the original SO-m DEM one's. Some watershed characteristics have good relation with entropy. Also, suggestions are made for calculating the lowest resolution of various errors based on different resolutions. The effects of DEM spatial resolution and sampling mothod on the model papameters and the modeling results are studied in this paper.