Dorset has several rivers that "disappear" seasonally. These include the North & South Winterborne Rivers and the Tarrant. The rivers give their names to the settlements they run through, the South Winterborne to Winterborne Abbas, the Tarrant to the likes of Tarrant Gunville, or Tarrant Hinton. The North Winterborne is fed by springs on Bulbarrow and runs through Winterborne Houghton, Winterborne Stickland, Winterborne Clenston, Winterborne Whitechurch, Winterborne Kingston, Winterborne Muston, Winterborne Anderson, Winterborne Tomson and Winterborne Zelston. The underlying rocks of Dorset's winterbourne streams are chalk.
Chalk is porous and soaks up rain like a sponge, storing it in the rock as groundwater. Winter rain percolates through the chalk and tops the groundwater levels up - usually at its highest in spring after the winter rain. As the groundwater levels rise, the water emerges as springs that feed the winterbournes. The springs can pop up anywhere along the riverbed or can be obvious such as at Wherry Pit at the head of the South Winterborne River. As groundwater levels fall through the late spring and summer, the springs dry up and the stream will stop flowing. The groundwater doesn't get much of a top up in the summer, even if it rains a lot, as vegetation and water evaporation mean that little rainfall soaks through to the chalk. However this can vary as we are all aware of soggy summers and dry winters.
Lower Winterborne Parish Council record that their river usually flows only during winter months, but the duration of flow depends entirely on rainfall during the year, e.g 1) In one particularly dry year in the mid-nineties, the river did not flow at all, and in another it flowed for just four weeks from mid-December to mid-January. 2) During the extremely wet winter of 2000/2001 the river flowed from early August 2000 to July 2001. 3) It started flowing in early September 2001 and, in Winterborne Kingston, stopped in early June 2002. In Winterborne Zelston the river was still flowing.
In most years the river behaves itself and flows within its banks, but in years of exceptionally heavy rain it overflows into the adjacent water meadows and, occasionally, onto the roads. The winter of 2000/2001 was particularly bad, with a number of roads closed due to flooding and a handful of cottages affected by floodwater. To overcome these problems in the future, North Dorset District council have carried out extensive flood alleviation measures throughout the Parish and time will tell how effective these will be. More details can be taken from the information board at the published co-ordinates.
In order to log your visit I would like you to undertake the following tasks:
1) Walk the short distance from the GZ to the reference co-ordinates. Here you will find a bridge over the river next to the church (where there are some lovely weeping willows). Please email the cache owner with the depth of flow on the day you visit (if any!), and state whether this would be considered normal or not? If not then state the reason why this might be?
2) In the last few decades the flow in the Spring Months has not been as great as in historical times. Email the cache owner with a reason why the water table may not be reaching up as high as it used to. There could be several reasons for this.
3) Email the cache owner with the year Winterborne Zelston won the Best Small Village award.
If you would like to add a photo showing the river / riverbed with yourselves then that would be great, but there is no obligation to do so.