Korving H, Clemens F
Witteveen + Bos Consulting Engineers, P.O. Box 233, 7400 AE, Deventer, The Netherlands.
Water Sci Technol. 2005;52(5):35-42.
Assessments of sewer performance are usually based on a single computation of CSO (combined sewer overflow) volumes using a time series of rainfall as system loads. A shortcoming of this method is that uncertainties in knowledge of sewer system dimensions are not taken into account. Moreover, sewer models are rarely calibrated. This paper presents the impacts of database errors and model calibration on return periods of calculated CSO volumes. The impact of uncertainties is illustrated with two examples. Variability of calculated CSO volumes is estimated using Monte Carlo simulations. The results show that calculated CSO volumes vary considerably due to database errors, especially uncertain dimensions of the catchment area. Furthermore, event-based calibration of a sewer model does not result in more reliable predictions because the calibrated parameters have low portability. However, it enables removal of database errors harmonising model predictions and 'reality'.
下水道性能评估通常基于使用降雨时间序列作为系统负荷对合流制下水道溢流（CSO）量进行的单一计算。该方法的一个缺点是没有考虑下水道系统尺寸知识的不确定性。此外，下水道模型很少进行校准。本文介绍了数据库误差和模型校准对计算出的CSO量重现期的影响。通过两个例子说明了不确定性的影响。使用蒙特卡罗模拟估计计算出的CSO量的变异性。结果表明，由于数据库误差，特别是集水区尺寸的不确定性，计算出的CSO量有很大差异。此外，基于事件的下水道模型校准并不会带来更可靠的预测，因为校准后的参数迁移性较低。然而，它能够消除数据库误差，使模型预测与“实际情况”相协调。
