34 Spartina Problems 



the rivers which discharge into it. In its present phase Spartina has an 

 insatiable appetite for mud with the result that much mud is being 

 transferred from lower to higher levels. As the new mud entering is 

 almost negligible in amount what is taking place is substantially of 

 the nature of a redistribution of mud already present. 



Corresponding to this phase a widening and deepening of the channels 

 is to be expected, an assumption which appears to agree with local 

 observation. 



As time goes on and the Spartina spread approaches its limits the 

 rate of assimilation of mud in the higher levels will be abated. The 

 early hunger for mud having been satisfied the final rise in level (as the 

 height of the flats approaches the limits of tidal rise) will be much more 

 gradual than in the preceding phase. 



Following such a redistribution of mud, two consequences are to be 

 expected. (1) Owing to the increased sectional areas of the channels 

 the rate of flow would be slowed and (2) the tidal water, being largely 

 displaced by mud in the higher levels, would occupy on the average a 

 lower level than was the case before the advent of Spartina. 



Both these effects, i.e. the slowing of the currents and the lesser 

 head of tidal water should work towards a diminution of scouring power 

 at the ebb. The mouth would thus tend to become encumbered with 

 silt to the impairment of navigation. 



But Poole Harbour is singular in its construction from the extreme 

 narrowness of its mouth. The area of the harbour is roughly 20 square 

 miles, whilst the outlet is only 350 yards wide. As a consequence the 

 harbour is stated never really to fill at high tide, i.e. to reach the full 

 height to which it is potentially entitled, because the tidal wave outside 

 passes the mouth too quickly. 



Based on the existence of a substantial difference in level between 

 high tide within and high tide without, the theory obtains locally that, 

 after all, Poole Harbour may prove immune to the usual consequences 

 of excessive silting. As the Spartina completes its work and the mud is 

 transferred from the bottom to the top, the tide will have less far to go 

 and will no longer waste the precious moments in excessive lateral travel. 

 On the contrary it is expected by local optimists that in fulness of time 

 the tide will rise in the channels to an appreciably higher level than it 

 does at present. Hence it seems to follow that, taken in connection with 

 the unexhausted head of water outside, Spartina is to be hailed as the 

 regenerator and not as the probable destroyer of the regime of Poole 

 Harbour. In other words the one thing required to remove the defect 



