Classification of hydrological conditions to assess water allocation schemes for Lake Baiyangdian in North China

Abstract

In this study an assessment framework based on analysis of water level fluctuations (WLFs) is presented to classify hydrological conditions and investigate the effect of recent water allocation to the lake of Baiyangdian. Good, moderate, and bad hydrological conditions in dry and wet periods are identified respectively using this framework. Annual average water level (AAWL) of moderate hydrological conditions is considered as the annual minimum water level (AMWL). The trend and determined range of intra-annual WLFs are estimated based on monthly optimum water level (MOWL) and monthly minimum water level (MMWL). Both estimated AMWL and intra-annual WLFs are compared respectively with AAWL and intra-annual WLFs observed in the corresponding year in order to assess recent water allocation schemes. Results show that in Lake Baiyangdian, a 16-year periodic component with alternation of dry and wet periods is found in the time series of water levels for 55 years. In dry period, the AMWL is 7.50 m with the determined range of intra-annual WLFs from 0.93 m to 1.04 m. While in wet period, the AMWL is 7.76 m with the determined range varying from 1.35 m to 1.56 m. The trend of intra-annual WLFs deduced by MMWL indicates that in both periods the maximum and minimum values of water levels appear in September and June, respectively. Assessment results suggest that recent water allocations for Lake Baiyangdian are irrational. Although, in some years, AAWL is higher than AMWL, ignorance of trend and determined range of intra-annual WLFs undermine the effects of water allocation. This framework can be used as a preliminary management tool for water allocation in degraded lakes.