We regularly sample water quality Monkton Crescent in Alderney, where the stream is culverted; it first reappears some 2.5km further downstream at Coy Pond Gardens.  The Coy Pond Gardens sampling site is slightly upstream of the stepped entrance to the gardens opposite Coy Pond and downstream of the small SUDS ponds created in November 2003.

It's clear from the charts below that water discharging from the culvert at Coy Pond Gardens has deteriorated somewhat in the underground sewer system.  

The 2003 stream improvements, and newly created ponds, were constructed to treating the water as it exits the culvert, leading to better conditions there and further downstream.  Results of ecological surveys before and after the works can be found here.

Sampling for the data presented below took place weekly over a 15 week period 12 May - 10 September 2003.

Although the stream is not a designated bathing water, it will give an indication of what the data represents in terms of water quality to compare them with the European Bathing Water Directive.  Coliforms are measured per 100ml of water:

However, the very high levels (2003 average) were affected to a huge extent by the heavy rainfall of 28 August (a total coliform count of 16 million!) following a 27-day dry period.

Taking 28 August out of the equation:

- an indication of how 'first flush' events can drastically effect stream water quality, and why it's important that we hold and treat such water wherever and whenever we can.

The charts below show a high input of total coliforms (bacteria), faecal coliforms (bacteria from human and animal waste), as well as Enterococci (also known as Faecal Streptococci, a pathogen found in human and animal waste) entering the stream in the culverted section.  

There is also some, but not a statistically significant, increase in suspended solids and BOD (biological - or biochemical - oxygen demand), both of which are further indications of poor water quality: