As a rule, an embankment across an estuary with one or two openings in it is to be avoided, and it should be most carefully considered whether it will not be better to expend a larger sum and erect a pile viaduct which will not interfere with the currents or channels and only require ordinary precautions to be taken against erosion, instead of depositing an embankment with openings at the channels and the necessary protective works which may consist of pitching the slopes, covering them with fascines, mattress work, or sods, erecting short or long, low or high, groynes, as the former may be ineffectual in causing a deposit or a shoal in front of the toe of the slope and in preventing scour, for in loose silty and sandy soil of considerable depth and not sufficiently firm to resist erosion, they will probably fail by reason of the space between them being washed away; and a complete covering of the foreshore may be requisite, or a protecting apron of homogeneous impermeable soil, and continuous training walls to prevent the creation of shoals: all of which protective works will constantly need to be repaired, and the failure of any one may cause not only an embankment to give way but the remaining preservative works. Undoubtedly there are many estuaries upon which if an embankment even with many openings for channels had been deposited, it would have failed, the soil being in such a tender state that the least additional weight upon the surface would destroy the equilibrium. Also interference with the littoral currents is a risky operation in any but a hard rock bed as regards the foundations, quite apart from injury to navigable channels. When there are numerous ditches, creeks, or channels crossing the line of a proposed estuary embankment of variable stability, especially should hills be near and the earth be so porous as to be saturated every tide, without doubt the safer plan is to erect a low viaduct, as the old waterways will be an endless source of trouble should the ground be anything but firm clay, and interference with the currents will not be preventable, as either their velocity will be increased or decreased, the result being scour or fresh deposits which will affect the channels; and such alteration may change the direction of the motion of the waters, which must be prevented in front of an estuary embankment; or waves will be created by the water travelling and rushing over shoals, for the even configuration of the bottom is a wave lessener, and should there be a deep channel near an estuary embankment severe wave action may be created. The piers or piles of such a viaduct should be cylindrical, thus offering no flat surface for the waves to break against, and yet temporarily to divide them without serious shock to a structure. When of very considerable length, a projecting embankment deposited upon a flat shore of a tidal estuary has caused a heaping up of the water on one side at low tide,