地表水蓄水的屈服能力通常不经常测试。然而，许多因素可能改变了蓄水的产出能力，尤其是如果在20-30年前进行了评估。公用事业经理应确保可靠的产量评估经常更新。包括8个参考文献、表格、图表。

The yield capability of surface water impoundments is not usually tested frequently. Many factors, however, may have altered the yield capability of an impoundment, especially if the appraisal was done 20-30 years ago. Utility managers should ensure that dependable yield appraisals are updated frequently. Includes 8 references, tables, figures.