求翻译：金沙江流域多年平均年降水量约710毫米；因流域广阔，支流众多，河川径流比较丰富且稳定，多年平均年径流量达1498亿立方米，构成长江干流比较稳定的基本流量。 是什么意思？

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Jinshajiang River valley for many years, an average annual precipitation of 710 mm wide; the basin, many tributaries and the river runoff is rich, stable, multi-year average annual run-off up to 149.8 billion cubic meters of the river, the more stable base flow.

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For many years the average annual rainfall in jinsha River basin of about 710 mm; basin wide tributary of large river runoff in a more rich and stable, multi-year average annual runoff of 149.8 billion cubic metres, constitutes the basic flow of main-stream of the Yangtze River is relatively stable.

Yangtze River basin multi-annual mean year precipitation approximately 710 millimeters; Because the basin is broad, the branch is multitudinous, the river runoff quite is rich also stable, the multi-annual mean year amount of runoff amounts to 149,800,000,000 cubic meters, constitutes the Yangtze Ri