The view from a small corner of Anglesey...
|Contact||Harvest Your Rain||Home|
The relative effects of a Pinus plantation on the hydrology of an Atlantic dune system. (Newborough Warren case study)
Martin Hollingham (2008)
Water levels have risen at Newborough between 1995-1996 and 2007-2008 on average 0.7m in the forest and 0.4m in the warren. The lower water levels in 1989-1996 compared to 2007-2008 are a result of the below average rainfall.
The difference in storage and hence the hydrological balance between the Forest, Border and Warren is only slight, accounting for 1% of P and is not significant. This contrasts with the expected difference of 10% of P more for the Forest , caused by differences in actual evapotranspiration (Freeman, 2008). During the years analysed, average annual storage fell by 2-3% of P , while drainage (29% of P) was greater than effective precipitation (26.5% of P).
Drainage increases with effective precipitation, which is to be expected, but storage falls even in years with high rainfall. This highlights the effects of the timing and intensity of episodic rainfall compared to the slow constant continual losses of actual evapotranspiration and drainage. Water levels rise within minutes in response to rainfall and decline slowly at a constant rate afterwards. The largest change in storage, -83mm for the Warren in 1989-1990 is less than the average actual evapotranspiration (96mm) for May and slightly greater than the average monthly rainfall (70mm).
The response of Forest storage and drainage to effective precipitation appears to be damped and limited compared to the Warren . This can not be due to recharge from the rock ridge. If this were the case, the Forest storage should increase more than the Warren in response to above average rainfall, which does not occur. This is most likely due to:
It appears that small additional evapotranspirational water losses from the forest are compensated for by a reduction in drainage from the Forest . Removal of the Forest will restore the hydrological balance of the felled areas to that of the Warren , but is unlikely to increase flooding within the Warren , as flooding is driven by the timing and intensity of rainfall.
Copyright © Martin Hollingham