首页 / 官方藏书 / River and Canal Engineering, the characteristics of open flowing streams, and the principles and methods to be followed in dealing with them. / 7. Intermittent Streams.—In the case of large streams whose flow is intermittent, the information required will, as before, depend upon the circumstances. Such streams occur in many countries. The difficulty in obtaining information is often very great. To obtain figures of daily discharge a gauge must be set up in the stream and a register kept. The chief difficulty in an out-of-the-way place is likely to be the obtaining correct information as to the maximum discharge. Information, derived from reports or from supposed flood marks, as to the highest water-level, may be inaccurate, and information based on rainfall figures may be extremely doubtful owing to the large size of the catchment area, the absence of rain gauges, and the difficulty, especially if the rain is not heavy, in estimating the available fall. All sources of information must be utilised and, whenever possible, observations should be made over a long period of time. 8. Remarks.—Very much remains to be done in collecting and publishing information concerning the ratio of the discharges to the rainfall. By observing a fall of rain and the discharge of a stream before and after the fall, it is possible to ascertain the figures for that occasion, but they will not hold good for all occasions. Continuous observations are required. The chief obstacle is the expense. Not only have measuring weirs and apparatus for automatically recording the water-level to be provided, but the weirs would often cause flooding of land involving payment of compensation. The most suitable places for making observations are those where reservoirs for water-works exist or are about to be made.

7. Intermittent Streams.—In the case of large streams whose flow is intermittent, the information required will, as before, depend upon the circumstances. Such streams occur in many countries. The difficulty in obtaining information is often very great. To obtain figures of daily discharge a gauge must be set up in the stream and a register kept. The chief difficulty in an out-of-the-way place is likely to be the obtaining correct information as to the maximum discharge. Information, derived from reports or from supposed flood marks, as to the highest water-level, may be inaccurate, and information based on rainfall figures may be extremely doubtful owing to the large size of the catchment area, the absence of rain gauges, and the difficulty, especially if the rain is not heavy, in estimating the available fall. All sources of information must be utilised and, whenever possible, observations should be made over a long period of time. 8. Remarks.—Very much remains to be done in collecting and publishing information concerning the ratio of the discharges to the rainfall. By observing a fall of rain and the discharge of a stream before and after the fall, it is possible to ascertain the figures for that occasion, but they will not hold good for all occasions. Continuous observations are required. The chief obstacle is the expense. Not only have measuring weirs and apparatus for automatically recording the water-level to be provided, but the weirs would often cause flooding of land involving payment of compensation. The most suitable places for making observations are those where reservoirs for water-works exist or are about to be made.

River and Canal Engineering, the characteristics of open flowing streams, and the principles and methods to be followed in dealing with them. · E. S. Bellasis · 第 1 / 8 章