Phoenix Adam Ltd are currently working on behalf of Jacobs, who were appointed by Scottish Water in April 2015 to undertake verification and solution development on the town of Annan in Scotland.

The project driver, as identified by the client, was to develop solutions to alleviate internal and external flooding at flooding clusters ‘E1618 Rose Street’ and ‘E1619 Hospital Road’ as identified from the flooding register.

One existing model was available for the town but this was considered not fit for purpose for assessing the current system performance and to develop flooding solutions. An existing model upgrade to current Scottish Water standards and verification against a short term flow survey was required for the half of the network which was hydraulically separate. For the requirement of this task Phoenix Adam Ltd scoped:

  • 7 Flow monitor locations
  • 4 Raingauges locations
  • Local drainage surveys for the 10 properties on the flood register in the two clusters of interest.
  • 1424m of CCTV surveys across the two flooding locations and surrounding network.

This section of the model was verified against an 11 week flow survey period.

The predicted flooding mechanism was assessed using InfoWorks CS and a design rainfall event of M5 for both winter and summer was used, as the flood register highlighted that most of the properties were affected 2 in 10 year period. Causes of flooding at the two clusters included a natural low spot in the street, surcharging up the system caused by network incapacity, and houses lower than street level. 2 potential options were developed for the two separate locations which included sewer upsizing to increase network capacity and storage tanks.

As the model build and verification was only on one half of the network it was requested in July 2015 that the scope of the project to be extended for model build and verification to be completed on the whole model prior to the option development of the two clusters. Additionally a third flooding cluster was added to the scope of the project, ‘Charles Street’. Following this the model was to be increased to a 10 year design horizon.

The extended scope meant that a new flow survey was scoped and managed by Phoenix Adam of 24 Flow/Depth Monitors, 4 Raingauges. Additional surveys of the town included Local Drainage of the additional flooding cluster, Impermeable Area Survey, Asset Survey, Topography Survey and Wastewater Treatment Works Survey. For this increased project a member of Phoenix Adam Ltd had a site visit to the town to assist surveying crews and gain a greater understanding of the town.

Model Verification of foul, combined and storm networks against the observed full flow survey focussing on specific days, using InfoWorks CS was undertaken, creating a current model. Critical duration storms were used for option development of the 3 flooding locations, developing solutions for the areas reduced flooding throughout the network. From this the model was uplifted to a 2030 design horizon, factors updated included:

  • Population Adjustments,
  • Water Consumption Adjustments
  • Trade and Commercial Flow Adjustments
  • Changes to Infiltration Sources
  • Application of Urban Creep
  • Application of Climate Change Impacts