weir crest in the usual manner. The weir which would be built up with the bridge is of concrete, laid in layers on the heart, but the crest and front slope would be faced with coursed masonry in the manner which before was advised. Owing, however, to the extra amount of land submerged to make a storage reservoir, a new cut had to be made into the mill race, as shown on the block plan, and a retaining-wall erected on the north bank of the river to prevent inundation of the surrounding lands. This was filled up at the back with the surplus excavation for the foundations, and the debris from the removal of the old weir and sand bags to clear out the river channel (see fig. 498). The roadway was formed together with the paths in the usual

manner.

Of course, what we have said regarding the cross section and design of

weirs in general must not in any way be taken as binding; like most engineering works, each case is considered on its own merits. Two forms of weir, having exceptionally flat slopes, and specially adapted to very large rivers, are shown by figs. 505 and 506. They would be formed of dry-stone, but the walls running through them, called nucleus walls, would be of solid masonry

or concrete.

Owing to the courtesy of Messrs Ransomes & Rapier, I am able to produce to the reader fig. 506A.

This illustration shows a range of four sluices made for Siam, for the purpose of controlling the flow from a river, and also keeping out tidal water

from the sea.

250'-o'

FIG. 506.

The sluices are therefore constructed to withstand pressure from either side.

In order to reduce obstruction in the river and provide as much discharge area as possible, the piers are constructed of steel sections instead of masonry. The whole of the structure is designed for bolting down to a solid mass of concrete.

Each gate is 20 ft. wide x 18 ft. 6 in. high, with a lift of 18 ft. 6 in., and is counterbalanced. The operating gear is carried on overhead girders at the top of the piers.

At each end of the range of sluices steel bulkheads, with piers similar in construction to the sluice piers, are provided, so that an earthen bank may be brought up close to the openings, and so avoid the usual abutments.

We said a few words previously upon Groins, and gave examples of such

as would be suitable for coast defence. We will now investigate the question as one which concerns a municipal engineer a little further.

* "The great struggle for mastery is always going on between sea and land, but only now and again, when a heavy gale occurs, is this warfare of the sea impressed on the public mind. The sea is making inroads on all our coasts, but more especially on the east coast. The coasts where high cliffs face the sea are more liable to erosion than low-lying land, and one may quote as an example some recent enormous falls of cliff at Dover. For this class of erosion

very little can be done towards arresting the inroad of the sea. In low-lying shingly places, however, numerous efforts have been and are still being made to counteract erosion. The principal localities of active coast erosion are between Bridlington and Spurn Point, and along the East Anglian coast. It has been calculated that the average loss of land between Bridlington and the Humber for many years was at the rate of from 24 yds. to 3 yds. per year, and that a width of two miles has been washed into the sea since the Norman

invasion; but of late years strenuous efforts have been made to arrest this erosion. Bridlington itself during the past thirty-five years has spent more than £70,000 in protecting its foreshore. The method that was adopted was to construct timber walls backed with chalk, and concrete and masonry walls. There is a continuous movement of shingle up and down the east coast, and in order to arrest this the most effective method has been found to be timber groins.

"The Board of Trade system of groins that is adopted between Kilnsea and Spurn Point and at the Point has been very successful, and has resulted in the accumulation of an immense quantity of shingle and sand. This system is shown in figs. 506в and 506c. Piles 12 in. by 12 in, of Baltic fir are * Building World.