The layout method of sampling sections for rivers should meet the following requirements:
(1) For urban or industrial river sections, control sections, reference sections and reduction sections should be set up.
(2) For severely polluted river sections, several control sections can be set based on the distribution of pollution sources and the pollution situation. The controlled pollution volume should not be less than 80% of the total volume of the river section.
(3) When there is a large tributary flowing into the river section, sampling sections should be set up at the upstream of the confluence point of the tributary and at the downstream of the fully mixed main stream.
(4) For international rivers or important inter-provincial rivers with sensitive water environment, sampling sections should be set up at the boundary of the administrative region of entry and exit.
(5) For river sections with stable water quality or where pollution sources have no significant impact on the water body, only one control section should be set up.
(6) Background sampling sections for rivers or river systems can be set up at the upstream close to the river source or in the sections that are not significantly affected by human activities.
(7) In river sections with hydrogeological or geochemical anomalies, sampling sections should be set up at both the upstream and downstream.
(8) Sampling sections should be set up at water supply sources, aquatic biological reserves, areas with waterborne diseases caused by water sources, and areas with severe soil erosion.
(9) Sampling sections should be set up 1000 meters upstream of the main water supply source of the city.
(10) Sampling sections should be set up at the estuaries of important rivers.
(11) In water network areas, sampling sections should be set up according to the prevailing annual flow direction; when there are multiple forks, they should be set up on the larger main stream, and the controlled runoff volume should not be less than 80% of the total runoff volume.