Phân tích tần số Theo bất tĩnh Điều kiện sử dụng đất Nhiều thiết kế thủy văn được dựa trên các ước tính cường độ lũ lụt liên quan với thời gian quay trở lại quy định. Lũ tần số phân tích dựa trên dữ liệu thu thập bởi các thiết bị cảm dòng có thể được sử dụng để xác định những biên độ lũ lụt. Trong trường hợp thay đổi sử dụng đất gắn với đô thị hoá, phá rừng, hoặc thay đổi trong hoạt động nông nghiệp trong lưu vực gaged, chuỗi thời gian tối đa hàng năm. | i o Frequency Analysis Under Nonstationary Land Use Conditions Glenn E. Moglen INTRODUCTION Many hydrologic designs are based on estimates of flood magnitudes associated with a specified return period. Flood-frequency analyses based on data collected by stream gages can be used to determine these flood magnitudes. In the event of land use change associated with urbanization deforestation or changes in agricultural practices within the gaged watershed the annual maximum time series recorded by the gage includes a trend or nonstationary component that reflects the effect of the land use change. Because urbanization typically increases the flood response of a watershed a flood frequency analysis performed on a nonstationary time series will lead to underestimation of flood magnitudes and insufficient underdesigned structures. Accounting for this nonstationarity is therefore essential for appropriate design. Overview of Method The method presented in this chapter may be used to adjust a peak-discharge time series that is nonstationary because of changing land use within the gaged watershed over the gaging period. The method has several parts. First the method focuses on deriving a spatially sensitive time series of land use. This step requires resourcefulness and creativity on the part of the hydrologist to obtain relevant data and to organize these data into a format most likely using making use of geographic information systems GIS technology that can be readily used to generate the values necessary as input to the hydrologic model. The next step is to calibrate the hydrologic model over the gaging period being studied while taking into account the spatially and temporally varying land use. The final step is to use the calibrated model to generate a synthetic time series of peak discharge related to the observed time series but adjusted to reflect a single land use condition such as the current or ultimate land use. This chapter examines the differences
