**Document:** Planning Statement Site Drainage **Application:** 13/01364/CON — Registered Building consent for works to existing retained Engine Room building (Registered Building Nos. 222) **Decision:** Application Withdrawn **Decision Date:** 2014-01-06 **Parish:** Braddan **Document Type:** report / planning_statement **Source:** https://planningportal.im/a/18805-braddan-former-laundry-site/documents/1315163 --- # Planning Statement Site Drainage ## The New Gateway Project, Tromode Industrial Estate, Carr's Lane, Douglas, Isle of Man for Clucas PLC ### Planning Statement Relating to Site Drainage #### Executive Summary - The proposed schemes for both foul and surface water drainage will be fully compliant with current regulations. - The proposed New Gateway development will have no adverse impact on the existing drainage systems or the adjacent properties. - It has been confirmed by Isle of Man Government, Water and Sewerage Authority (WASA) that there is adequate capacity within the existing combined system for connection of the foul sewers, this connection has been agreed with WASA. - The surface water drainage is outlined to discharge in to the River Glass and, with the use of attenuation has been designed not to surcharge during a 1 in 5 year river flooding event as specified by WASA. ## 1. Introduction 1.1. This statement has been prepared by BB Consulting Engineers Ltd. in support of a Planning Application for the proposed New Gateway industrial unit development at Tromode Industrial Estate, Carr's Lane. The proposed development is on a brownfield currently occupied by the now disused Clucas laundry as well as several smaller industrial units. The demolition of these existing buildings is subject of a separate planning application. This statement covers surface water and foul drainage. 1.2. Reference is made to BB Consulting Engineers Ltd., McGarrigle Architects and Hyder Consulting drawings submitted within the Planning Application. ## 2. Site Description 2.1. The site is located within the Tromode industrial estate on Carr's Lane off Johnny Watterson's Lane Douglas, Isle of Man. 2.2. The site currently encloses the Clucas laundry as well as several smaller industrial units. The existing buildings within the site extents are to be demolished. 2.3. The existing hard standing areas have a general fall from north east to south west. 2.4. The site is bounded to the east by an embankment and to the west by a concrete highway which runs adjacent to the River Glass. 2.5. The proposed site is brownfield. 2.6. The site is approximately 7600m² and of an impermeable nature. 2.7. Previous development of an adjacent site has indicated that the sub-soils are generally a moderately compacted gravel with water table at approximately 1.8m below ground level. Due to the nature of the existing services within the hard standing areas a full site investigation is to be undertaken following the demolition of the existing buildings. The strata exposed during previous investigations are viewed as suitable bearing material for the proposed developments foundations. ## 3. Existing Drainage Characteristics 3.1. The River Glass runs adjacent to the site flowing southwards where it outlets in to Douglas Harbour. The position of the site can be viewed as being within the lower reaches of the catchment. 3.2. There is an existing mill race which enters the site to the north east of the site. The mill race splits in two tail races which run through the site and discharge in to the River Glass. The tailraces are currently utilised as part of the surface water drainage system for the existing site. 3.3. From existing records and site observations a proportion of the surface water runoff from the existing buildings and hard standing discharges in to the WASA adopted combined sewerage system which runs adjacent to the River Glass eastern bank. 3.4. The existing foul water drainage discharges in to the WASA adopted combined sewerage system. ### 4. Foul Drainage 4.1. The proposed foul water drainage system is outlined for connection in to the WASA combined sewer which runs adjacent to the highway. Connection is proposed through an existing foul tail which branches in to WASA manhole #1801. This connection has been agreed with WASA. 4.2. The proposed layout and topography of the site permits the use of a gravity foul drainage system. ### 5. Surface Water Drainage 5.1. The proposed surface water drainage system is outlined to discharge in to the River Glass. The existing surface water discharging in to the existing combined sewer will be removed and therefore there will be a reduced storm flow within the existing combined sewer. 5.2. The proposed layout and topography of the site permits the use of a gravity surface water drainage system. 5.3. The existing mill race which enters the site at the north east boundary is proposed to be culverted at the site boundary and introduced in to the proposed surface water system. 5.4. The redundant tail races which run within the site are to be decommissioned and backfilled. 5.5. There is a proposed vehicle wash down facility to the rear of unit 8. This area is to have isolated surface water drainage to the hard standing and drain through an oil bypass interceptor which will discharge in to the surface water system. 5.6. WASA have requested that the surface water system is designed not surcharge due to the River Glass at a 1 in 5 year storm event. The proposed outlet level of the surface water system lies below the 1 in 5 year River Glass flood level, in order to prevent surcharging a flap valve is to be introduced at the outlet. During periods where the surface water system cannot discharge in to the River Glass it is proposed that the flows will be attenuated within the site and this attenuation volume will utilise a 1 in 5 year storm event river level as the design criteria. 3 ### 6. Drawing Schedule 6.1. 13-096/10 – Proposed Site Drainage BB Consulting Engineers Limited 27 Duke Street, Douglas IM1 2AZ 15 November 2013 Z:\01 JOBS\2013 Jobs\13-096 - Gateway Project, Tromode Estate\06 Reports & Docs\13096-131115-nq-PlanningDrainageStatement.docx 4 --- *Data sourced from the Isle of Man public planning register under the [Isle of Man Open Government Licence](https://www.gov.im/about-this-site/open-government-licence/).* *Canonical page: https://planningportal.im/a/18805-braddan-former-laundry-site/documents/1315163*