Should the source be known from which the water issues the drainage may be local, and if a spring be unsealed it may be necessary to insert pipes in the slope, for until the spring is tapped and guided no system of drains may be effectual. By inserting a stand-pipe over a spring, the height to which the water will rise will approximately show the head-level of the supply. If possible, this should be ascertained, as it may happen that the water can be drained by gravitation in pipes without much excavation being required in the slopes or formation; but care should be taken that no water is allowed to settle or accumulate for the purpose of its being conducted away unless upon a protected surface. With regard to catchwater drains upon the cess at the top of the slopes, they should be cut before the excavation is commenced; and it is important to remember that instead of their affording protection by guiding the surface waters, which would otherwise proceed towards the slopes, they may increase the percolation by localizing the water and allowing it to accumulate and find its way to the slope; and in sidelong ground it may, therefore, be necessary to protect their valley more than their uphill side, as the surface water will impinge against it; but when they are practically impervious and gently direct the surface water they are advantageous, and in permeable soil, unless they are so constructed as to be impervious, perhaps it is better to have none. They should be as reasonably distant from the top of the slope as is convenient without weakening the foundations of the posts supporting any fencing, and in order to quickly discharge the water and lessen the chance of their becoming choked by detritus or ice, they should have considerable inclination. As the adoption of even a moderate fall in the drains may erode the side ditches and cause water to percolate to the slopes and make a water-seam, it may be necessary to protect the bottom, and as the depth of the side drains in order to be effectual may be considerable, according to the character of the soil, the sides may also require to be covered and supported. In cuttings in many soils sufficient stones can be picked out to cover the surfaces of the side drains, and they can be roughly packed, the smaller stones being rammed into the interstices between the larger, which will gradually become filled; also a covering of brushwood, rammed earth, or puddled clay can be used, or other expedient which occasion may suggest. The inclination must not be steeper than the natural or protected bed can bear without the water scouring it, and yet should be sufficient to prevent any deposit or choking, and the drains should be cleared regularly, and especially in the autumn in England or before the wet season commences, and all depressions in which water can accumulate should be levelled in order to assist easy discharge. Small open drains become choked somewhat