水电站上、下游水位的差值。上游水位减去下游水位称毛水头。毛水头减去水头损失，称净水头。水头损失是指上游水流由取水口(前池或调压井处)经高压管道至蜗壳进口断面这一过程中的局部水头损失和沿程损失之和。由于水电站上、下游水位是经常变化的，年内上、下游不同水位实际出现的各种组合将形成不同的水头值，其中数值最大者为最大水头，数值最小者为最小水头。平均水头可用不同的公式计算，最简单的方法是取最大水头和最小水头的算术平均值。
河床式水电站水头比较低，而单机流量通常较大，这样水电站厂房的进水口、蜗壳和尾水管等尺寸较大。
In general, the head pressure of power station in river channel is lower comparatively, but the unit discharge is always greater, in this way, the dimension of the hydropower house is usually larger.
小湾水电站泄洪洞在泄洪时具有高水头、高流速、泄量大的特点，对混凝土冲刷力强，容易产生空蚀破坏。
As the high head, high velocity and large flow of flood discharge, the concrete of spillway tunnel in Xiaowan Hydropower Station is easy to be damaged by cavitation.
大流量高水头水电站泄洪消能型式的选择，是完善枢纽布置和各项功能的重要环节。
For large discharge and high head hydropower stations, the selection of energy dissipation mode is an important part for improvement of structure layout and various functions.
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