Northumbrian Water Drainage Area Studies

 

These Drainage Area Study projects provided a sustainable, robust and structured approach to the proactive assessment of hydraulic capacity of the Northumbrian Water Ltd (NWL) sewerage network. We achieved this through a prioritised programme of hydraulic analysis and monitoring, targeting those locations with the greatest risks associated with hydraulic failure.

NWL’s objective is, over time, to reduce the number of escapes from the public sewerage system from storm events with a return period of less than 1 in 20 years to as near zero as possible. Priority is given to preventing internal property flooding from wastewater infrastructure.

 

Above: Eaglescliffe 3D overview

To support attainment of this objective we :

  • Developed hydraulic models incorporating current and future scenarios to identify locations where there are high risks of flows escaping from the public sewer network,
  • Promoted feasible options for preventing those escapes which would result in internal property flooding (short term and longer term options) and,
  • Identified key locations where ongoing performance monitoring will be required.

We used a combination of new build and existing model upgrade to develop a 1D WaPUG Type 2 model. We used data as supplied by NWL New Development to establish current and future growth and to establish existing and future flows and loads and their impact on NWL assets. We generated Flood Estimation Handbook (FEH) rainfall and used this in simulation to identify risk locations and flooding sources.

Following on from our 1D model build we developed 2D models of each scenario. We applied a 2D mesh with building voids across the entire model based on 2m LiDAR and superimposed a separate, more highy detailed mesh on the main catchment mesh to more accurately represent roads channels.

Above: Stockton South 3D overview

We undertook an assessment of existing real world data specific to the catchment, such as historic rainfall events and customer flooding reports. We then verified the 2012 2D model against this data. 

An additional modelling complexity was the need to develop time varying level hydrograph files for some models as a boundary condition to simulate tidal levels in the Tyne estuary.  The simulations used three scenarios, diurnal Mean High Water Spring tide, Mean Sea Level, and Mean Low Water Spring tide levels, with coincident high tide and storm peak for a conservative output.

We identified ‘hot spot’ flood risk areas that require further detailed assessment.  We used modelled flow depth and velocity together with topographic flood routing (InfoWorks 2D) to provide an assessment of the consequences of the incapacity. Future scenario modelling reflected potential impacts of legislation, growth, creep and climate change on the sewer network.

 

We developed outline solutions or prevention of internal property flooding in each of the hot spot areas.  We proposed a wide range of options, including property level protection, surface water management measures, monitoring and operational interventions, sustainable drainage solutions (SuDS), as well as traditional network upgrade proposals.

 

Our outline solution development also included identification of “quick wins”, constraints, potential benefits (e.g. flood risk reduction, reduced CSO spill, improved water quality / amenity value, asset life expectancy, carbon impact) and indicative costs.

 

Phoenix Adam Ltd operates under ISO9001 UKAS accreditation. Outputs were subject to our ISO9001 Check, Review, Approval and Verification process.