MEETING OF DÚN LAOGHAIRE AREA COMMITTEE

26 MARCH 2018

TRIMLESTON STREAM,

Question: Councillor C. Devlin

“To ask the Chief Executive to provide a detailed report including maps of the origin and route of the Trimleston Stream, Booterstown and what assessments or actions have been taken by Dún Laoghaire-Rathdown in relation to this stream over the past 5 years?”

Reply: 1. Route and Origin The Trimleston Stream enters the sea at Booterstown along the north edge of Booterstown Marsh. The above maps show the route of the stream. The red line indicates where the stream is culverted and the blue where it is an open stream. The only open section of the stream runs for approximately 500m to the rear of 1 -34 Trimleston Gardens and 1A to 14 Trimleston Ave. At Fosterbrook apartments, two culverted tributaries come together. One leg (1050mm diameter) comes from south west direction running having crossed the N11 close to Foster’s Ave. The other leg comes from the east and picks up surface water drainage in the Seafield Estate.

2. Assessments 1. In 2014, a structural risk assessment of the screen that protects the culvert that crosses beneath the Rock Rd was carried out by JBA Consulting on behalf of DLR. 2. The stream is sampled (just upstream of its discharge to sea) three times a year by DLR staff. 3. The stream is part of the European Funded Intereg “Acclimatize” Project currently being undertaken by University College . The purpose of the project is to identify sources of pollution and their impact on bathing waters as a result of climate change. DLR Staff have been assisting UCD personnel in relation to sampling the stream and also the installation of a flow monitor to measure flows. 4. DLR conducted a misconnection survey of the Trimleston Stream Catchment from October 2015 to March 2017. 1093 homes were surveyed. 38 were misconnected. 5 of this number contained 5 misconnected toilets. 5. There are 3 Irish Water overflows from the foul sewer network to the stream. Also there is a pump station (St Helen’s Pump Station) that can overflow (in the case of blockage, power failure or over capacity) to the stream. The pumps were replaced by Irish Water in 2015. 6. Sampling results from the Trimleston Stream have been included in a number of assessment reports of water quality at Merrion Strand by Dublin City Council.

From “The Rivers of Dublin” by Clare Sweeney “This small stream starts at Mount Merrion south of St Teresa’s Church near Tree’s Road and passes through Mt Merrion housing to a point just south of Foster’s Avenue Rd Junction and over to St Helens Novitae Lands. It carries on by the house to the rear of Trimleston Gardens houses (east side) and the rear of the west side house on St Helen’s Rd until it meets the Merrion Rd. Crossing the Road the stream culvert continues by the side of the salt march over to the Nutley Stream, the DART rail and the sea at Merrion Stream”

Owner: Gerry Concannon, A/Senior Engineer, Water Services