2.5　Sediment，Evaporation，Ice Regime

2.5.1　All or part of the following sediment information at the dam（plant）site shall be provided as required by the design of a hydropower station:

1　Mean annual sediment discharge of suspended load，and sediment discharges of suspended load in high-sediment year，median-sediment year and low-sediment year，and their intra-annual distributions.

2　Mean annual sediment concentration of suspended load and actually measured maximum sediment concentration.

3　Sediment gradation of suspended load，median particle diameter and maximum diameter of sediments.

4　Mean annual sediment discharge of bed load.

2.5.2　Computation of sediment of suspended load for the hydropower station may be conducted by using the following methods based on the data available:

1　If sediment measurement data is available for the upstream and downstream of dam site or the river basin，the sediment characteristic values from the bench-mark station may be used after modification of the area.

2　If sediment measurement data is limited or unavailable for the river basin where the hydropower station is located，the sediment characteristic values may be estimated according to sediment measurement data from adjacent river basins or regional comprehensive chart of erosion modulus.

2.5.3　The mean annual water surface evaporation and its intra-annual distribution of the hydropower station reservoir may be calculated based on data from the evaporation station in the river basin or adjacent areas，or on the regional comprehensive chart of evaporation.

2.5.4　For the river reach with ice regime，information to be provided shall include:status of river reaches during freezing and thawing periods；earliest and latest dates of emergence of border ice，drift ice，freezing-up and thawing of the whole river；thickness of frozen ice，size of drift ice，and date，place and scale of occurrence of any ice jam and ice dam.