THE FAUNA OF THE EXE ESTUARY. 297 



Mr. E. H. Worth, will be useful in comparing the Exe estuary with 

 that of Salcombe. The watershed area draining to the Exe estuary- 

 is 584 square miles, the area draining to the Salcombe estuary is 

 33 J square miles, and the rainfall over the two areas is about the 

 same. It would not, however, be correct to say that with any given 

 rainfall the flow of fresh water passing into the Salcombe estuary 

 would therefore be only one-seventeenth of that passing into the 

 Exe estuary, for both in summer and winter, but more especially in 

 summer, the larger catchment would give a greater ordinary flow per 

 unit area, whilst in time of exceptional flood this condition might 

 be reversed and the smaller catchment would yield from twice to, 

 in extreme cases, four times as much water per square mile. It would 

 probably not be exaggerating the difference between the two estuaries 

 to assume that the fresh water flowing into the Salcombe estuary is 

 in summer one-thirtieth that flowing into the Exe estuary, in winter 

 one-twentieth, at times of considerable flood one-tenth, and at times 

 of great flood one-fifth. On the other hand, each flood of the Exe 

 would last for a longer time than a flood at Salcombe. 



The area of the Salcombe estuary at high tide is about half that 

 of the Exe estuary, whilst at low tide, taking the whole length of each 

 estuary, the two are more nearly equal in area. The Salcombe low- 

 water channel is much the deeper, and the average rise and fall of tide 

 is somewhat greater at Salcombe than at Exmouth. On the whole, 

 therefore, it appears that the water of the Exe estuary must, at certain 

 times at any rate, be of much less density than any which even in 

 times of flood runs through the Salcombe estuary. 



These conclusions are confirmed by the following observations of 

 the density of the water in different parts of the estuary, made by 

 Mr. Todd in December, after a night of heavy rain following a period 

 of average rainfall (all samples taken at the surface) : — 



December 12th, 1901. High tide at Exmouth, 7.16 a.m. Neap tides. 



[Height of tide at Plymouth, 14 ft. 1 1 ins.] 



Starcross (Pier), 11.15 a.m. Temperature, 9-2° C. ; density at that 



temperature, r021. 

 Exmouth (north side of Pier), 11.40 a.m. Temp., 97° C; density, 1-0248. 

 Exmouth Dock, 12.25 p.m. Temp., 9-4° C. ; density, 1-0235. 

 Exmouth (south side of Pier), 12.35 p.m. Temp., 8-6° C; density, 1-021. 



12-50 p.m. Temp., 8.4° C. ; density, 1-0208. 

 1.5 p.m. Temp., 8-4° C. ; density, 1-0204. 

 Topsbam, 2 p.m. Temp., 11-9° C. ; fresh water. 

 Woodbury Road, 3.45 p.m. Temp., 8° C. ; fresh water, 

 Exmouth (south side of Pier), 5.30 p.m. Temp., 9-8° C; density, 1-0259. 

 Starcross (Pier), 6.5 p.m. Temp., 9-5° C. ; density, 1-0262. 



