Embankments should, where possible, be made in straight or properly curved reaches. A flood embankment, at least at its upstream end, should terminate in ground which is above flood-level. The top of an embankment should be, in the case of a large river, 2 or 3 feet above the high flood-level of the river. It should, of course, be graded parallel to the general high flood-level, but neither the gradient nor the height of the flood is usually known with accuracy (CHAP. II., _Arts. 1_ and _2_). There is generally a record or mark of some high flood, and this is taken provisionally as the flood-level. Or the level is calculated approximately from the flood readings on the nearest river gauge. If experience shows that the embankment is too low, it is raised. The cross-section of an embankment depends on the soil, on the extent of damage which results if a breach occurs, on the funds available, and on the value of the land which the embankment has to occupy. Where an affluent enters the river it will probably be necessary to run out branch embankments. Sometimes cross embankments are run from the main embankment to high land. Their object is to localise the damage if a breach occurs. Along the back of the embankment there may be a drain and it can be made to discharge its water, when the river is not in flood, through the embankment by means of sluices or by pipes closed by flap valves which will not allow flood water from the river to pass through. There may be sluices in the embankment for the purpose of irrigating the land at the back. The immediate effect of the construction of flood embankments along a river is to raise the water-level, because the floods can no longer spread out over the country, but this effect will not be great if the sectional area of the flood water was small or its velocity low. The river may or may not tend, after the construction of flood embankments, to raise or lower its bed. It has already been remarked that questions of silting or scouring cannot be answered in a general manner. In the case, however, of floods spilling over a piece of country, the depth of the flood water is generally small and the country more or less obstructed. Some deposit of silt generally occurs. The construction of an embankment reduces the area of the flood water, and thus generally reduces the silting and leaves more silt in the river proper. The depth and velocity in the river are increased. Everything depends on which is increased most. Most likely the stream is of shallow section and the velocity is increased most (CHAP. IV., _Art. 6_, par. 6), and the increased silt-supporting power may make up for the increased charge of silt.