Considering all projects or components of components of the whole basin as a unit or several suitable units to assess the whole environmental impacts on the upper part (above the lowest cascade) of the basin.

• 把方案中的各种工程作为一个大单元或分成几个组成单元，评价各方案对最下一级工程以上地区各种环境因子及地区(流域)的总体影响。