The changing face of Shijiu Lake

Survey

Shijiu Lake lies in the south-west of Lishui District. It is the boundary lake between Lishui and Gaochun districts and Dangtu County in Anhui, and belongs to the Shijiu Lake river system (District Government, Geographical Position page). The main watercourse draining the Lishui side into the lake is the Xinqiao River: it rises at the Laoyaba Reservoir and runs about 31.4 km with a catchment of 314.6 sq km (text on the Xinqiao River improvement works).

Area. The Gaochun District "Natural conditions" page states the change directly in its text: "the original area was 266.7 sq km; after reclamation by the districts along the shore in the 1970s, the open water shrank to 207.6 sq km". This is the only government page found for this site that puts the two figures, before and after reclamation, side by side, but it gives only the rough date "the 1970s" and no year-by-year figures. The same page describes Gaocheng Lake and Danyang Lake in the same way, so this is how the page routinely tells the story of all three lakes.

Protected status. In November 2019 the Jiangsu Provincial Forestry Bureau approved the establishment of the Lishui Shijiu Lake provincial wetland park, with a planned area of 91.7 sq km (Nanjing Municipal People's Government, reply to suggestion No. 0312 of the Municipal People's Congress); boundary markers and signs for the provincial important wetland (provincial wetland park) were sited and installed afterwards. The Jiangsu provincial list of important wetlands carries a row for Shijiu Lake, Lishui District, with an area of 9140.71 ha. Under the district territorial spatial master plan, the district has drawn five ecological protection red lines totalling 119.7322 sq km, covering nature protection areas (forest parks, wetland parks) and drinking-water source protection areas.

Dikes. The lake dikes have been the main object of works over these decades. According to the 2014 environmental impact report for the Nanjing Shijiu Lake and Gaocheng Lake dike flood-capacity improvement works, its review of the existing dikes records that "in 1999-2002 Nanjing strengthened the lake dikes, to a flood standard of about 1 in 20 to 1 in 40 years"; in that improvement project the Lishui reach of Shijiu Lake had 30.42 km of lake dike and 4.31 km of harbour dike strengthened, 34.73 km of dike in all, with 85 structures, a 1-in-40 year flood standard and grade 3 dikes, a design flood level of 12.50 m, a dike crest at 14.50 m and a rear berm at 11.00 m, at a total investment of 639.7583 million yuan. The Gaochun reach has 13.57 km of dike, grade 2, with a 1-in-50 year standard. The task of the works was to protect the 214 sq km of polders along the lake, and that figure is the combined protected area of the whole project (Shijiu Lake and Gaocheng Lake), not the polder area of Lishui District.

Periods and areas

This article uses four periods that the sources support, and sets out the administrative and engineering divisions of the lake alongside them.

First period: reclamation in the 1970s. Reclamation by the districts along the shore cut the open water from 266.7 sq km to 207.6 sq km (Gaochun District, "Natural conditions" page). The official text for this period goes no further than "the 1970s" and the two total figures; there are no year-by-year reclaimed areas, reclamation years or project names.

Second period: strengthening of the lake dikes in 1999 to 2002. Nanjing strengthened the lake dikes, bringing the flood standard to about 1 in 20 to 1 in 40 years (2014 environmental impact report, review of the existing dikes).

Third period: the flood-capacity improvement works around 2014. The report gives the design basis: the Lishui reach to a 1-in-40 year standard with grade 3 dikes, the Gaochun reach to 1 in 50 with grade 2 dikes; urban reaches to 1 in 50 with grade 2 dikes and non-urban reaches to 1 in 40 with grade 3 dikes; structures through the dikes taking the same grade as the dike they cross (ibid.).

Fourth period: protected status since 2019. The provincial wetland park was approved in November 2019 with a planned area of 91.7 sq km; the lake was then listed in the Jiangsu provincial list of important wetlands with an area of 9140.71 ha; and the district territorial spatial master plan folds the nature protection areas, the wetland park among them, into the district's five ecological protection red lines (Nanjing Municipal People's Government reply to the suggestion; Jiangsu provincial list of important wetlands; master plan Article 20).

Areas. By jurisdiction the lake spans Jiangsu and Anhui: the provincial list of important wetlands carries only the single row for Shijiu Lake, Lishui District, and the dike works were designed separately for the Lishui and Gaochun reaches (ibid.). By engineering, the 2014 improvement works designed the two reaches separately: 34.73 km of dike in the Lishui reach at a 1-in-40 year standard and grade 3, and 13.57 km in the Gaochun reach at 1 in 50 and grade 2, with the structure counts, investment and construction period listed separately for each reach in the report.

Open questions

• Four kinds of area figure, not interchangeable: the lake area of 207.6 sq km after reclamation and the original 266.7 sq km form one group (Gaochun District page); the 9140.71 ha of the provincial important wetland (the list) and the 91.7 sq km planned area of the provincial wetland park (the reply to the suggestion) are protection-area figures; the 599.39 sq km of the Shijiu Lake basin (District Government, Geographical Position page) is a basin figure. Their magnitudes and meanings all differ, and they must not be compared or added together.
• The reclamation has only a rough date: the Gaochun District page gives "the 1970s" and no year-by-year area, year or project name. This article therefore does not state how many square kilometres were reclaimed in any given year, and does not infer the reclaimed area within Lishui District from it.
• No official document found on returning polders to the lake: the page carries no wording on "returning polders to the lake" or "returning fish ponds to the lake", nor any implementation year, and this site has not found an official document on returning polders to Shijiu Lake. This article therefore states neither a date nor an area for such a change, and does not reason by analogy from other lakes.
• The "214 sq km of polders along the lake" is the combined protected area of the whole project (Shijiu Lake and Gaocheng Lake), not the polder area of Lishui District, and must not be mixed with the "293.52 sq km of low-lying polders".
• The 119.7322 sq km of ecological protection red lines is the combined area of the district's five red lines, not the area of Shijiu Lake alone; the lake appears in it only as one of the nature protection areas (a wetland park).
• The 9140.71 ha of the provincial important wetland and the 91.7 sq km planned area of the provincial wetland park are both protection-area figures, drawn on different bases and covering different extents, and must not be converted into one another or used interchangeably.
• The 31.4 km and 314.6 sq km of the Xinqiao River are that river's length and catchment, not the shoreline or lake area of Shijiu Lake.