Water, sediment and nutrient budgets for Somerset and Wivenhoe reservoirs, Australia

Annual inputs and outputs of water, total suspended solids (TSS), total nitrogen (TN) and total phosphorus (TP) were estimated for two reservoirs over 14 years from July 1997 to June 2011. Somerset and Wivenhoe are major drinking water and flood mitigation reservoirs in southeast Queensland, Australia (27° 7' S, 152° 33' E and 27° 24'S, 152° 36' E, respectively), and they are linked by the Stanley River. Inflows are highly episodic and concentrated in the austral summer ("wet season") therefore data is provided for "water years" defined from July to June. Annual inputs of water, TSS, TN and TP from the catchments were estimated from daily flow and loads predicted by the Source Catchments (SC) model. Loads of TSS, TN and TP exported from the reservoirs were calculated by multiplying concentrations measured at the dam walls by the volumes of water released, and integrating over annual timescales. Concentrations of TSS, TN and TP were primarily from monthly water quality sampling, with missing data during December 2010 and January 2011 estimated from hourly turbidity profiles. Annual retention in each reservoir is the sum of catchment inputs (SC model predications) and loads from the upstream reservoir (in the case of Wivenhoe), minus reservoir outputs. There were four notable hydrological events during the study period: a major drought from 2001 to 2009, high flow in February 1999 and February 2008, and a major flood in January 2011. Uncertainty was quantified for all terms, but confidence in the uncertainty estimated for the period July 2010-June 2011 was low due to the large scale of the January 2011 flood. A full description of methods for determining loads and uncertainty is available in O'Brien et al. 2016.

1997年7月至2011年6月的14年间，本研究对两座水库的水、总悬浮颗粒物（total suspended solids, TSS）、总氮（total nitrogen, TN）及总磷（total phosphorus, TP）的年度收支状况开展了估算。萨默塞特水库（Somerset）与威文霍水库（Wivenhoe）是澳大利亚昆士兰州东南部的核心饮用水供应与防洪调蓄水库，二者坐标分别为27°7′S、152°33′E与27°24′S、152°36′E，且通过斯坦利河（Stanley River）实现水系连通。流域径流具有极强的间歇性，且主要集中于南半球夏季（“湿季”），因此本数据集采用7月至次年6月的水文年（water years）作为统计周期。流域输入的水、TSS、TN及TP年度负荷量，通过每日径流数据与Source Catchments（SC）模型模拟的负荷结果进行估算。水库输出的TSS、TN及TP负荷量，则通过坝体断面实测污染物浓度与泄放水量的乘积计算，并按年度尺度完成积分求和。TSS、TN及TP的浓度数据主要来自月度水质监测，2010年12月至2011年1月的缺失数据通过逐小时浊度剖面数据完成补全估算。两座水库的年度污染物截留量，等于流域输入负荷（Source Catchments模型模拟结果）与上游水库的输入负荷（仅针对威文霍水库）之和，减去水库自身的输出负荷。本研究周期内共发生4起显著水文事件：2001-2009年的持续特大干旱、1999年2月与2008年2月的强径流过程，以及2011年1月的特大洪水。所有参数项的不确定性均已量化，但受2011年1月特大洪水的影响，2010年7月至2011年6月期间的不确定性估算结果置信度较低。有关负荷计算与不确定性分析的完整方法，可参见O'Brien等人2016年的研究成果。