SEA-FISHERIES LABORATORY. 435 



ON THE DRIFT OF SEWAGE IN THE ESTUARY 



OF THE MAWDDACH IN RELATION TO THE 



MUSSEL BEDS. 



By Fred. W. Durlacher, 

 University College, Aberystwyth. 



(With Chart.) 



My observations at Barmouth extended over a period 

 of 10 days, and the methods followed were precisely the 

 same as at Aberdovey. 



Possible sources of contamination are the two main 

 sewers, whose positions and those of the mussel beds, are 

 shown on the accompanying map ; the privies on the quay, 

 emptying directly into the water or on to the sand beneath ; 

 and five or six drains which discharge from as many 

 houses on the cliff at Aberamffra. Of these there need 

 scarcely be any doubt that the first sewer, situated a mile 

 or so North of the harbour, can be neglected. During my 

 stay the weather was too rough to allow of a practical 

 verification by means of floats of the direction of the drift 

 from these pipes; nevertheless, it can be taken as practi- 

 cally certain that the flood tide carries the sewage away 

 towards the North, and the strong flow oul of the estuary 

 prevents any sewage entering the River on the ebb. 



The tidal scour of the estuary is very strong, the 

 speed of the flow at springs beneath the iron railway 

 bridge being about 5 miles per hour, while the flow over 

 the mussel beds at Aberamffra at similar periods is from 

 2-3 miles per hour. At neaps this rale is reduced by about 

 one-half. 



