England’s Strategic Trunk Road Network Wastewater Conference – 2019 Managing Highway Runoff Santi. V. Santhalingam Owner of Drainage Standards Lead Drainage Specialist & Team Leader
Outline of Presentation ▪ Introduction ▪ Objectives of drainage ▪ Common drainage methods ▪ SUDS, WFD and Floods & Water Management Act ▪ Basic design considerations ▪ Key standards for design & construction ▪ Climate Change ▪ Key standards for operation and asset management ▪ SMP and RIS & RIP Schemes – the way forward ▪ Opportunities for collaboration
Introduction ▪ Highways England is a government company charged with operating, maintaining and improving England’s motorways and major A roads – Formerly the Highways Agency, Highways England became a government company in April 2015 ▪ The strategic road network is vital for the UK economy and is relied on by communities and businesses nationwide ▪ Our primary aim is to ensure our strategic road network is more reliable, resilient and safe
The Strategic Road Network 2 % England’s Roads – over 7000km ▪ (4435 miles) out of 292,000km (182,000 miles) ▪ 1, 865 miles of Motorways & 2571 miles of Trunk A-roads ▪ Carries 1/3 of all traffic and 2/3 of all freight ▪ Roads 200,000 vpd to <10,000 vpd ▪ 7 Regions - Managed by 13 Area Teams (MACs) and a number of route based (DBFO) service providers ▪ Total Asset Value = £ 114bn – Drainage asset value = £ 20 bn
Drainage Objectives ▪ Speedy removal of water – To provide safety and minimum nuisance to users ▪ Effective sub-surface drainage – To maximise longevity of pavements and earthworks ▪ Control of run-off related pollution – To minimise the impact on the aquatic environment
Drainage Elements Surface Drainage water that runs on the surface Sub-surface Drainage water that is able to infiltrate road layers
Common Surface Drainage Methods ▪ Kerb and Gullies ▪ Surface Water Channel ▪ Combined Filter Drain (French Drain) ▪ Over the Edge drainage ▪ Drainage Channel Blocks (and Grips) ▪ Combined Kerb and Drainage Units ▪ Linear Drainage ▪ Grassed Surface Water Channel ▪ Ditches, Soakaways and Ponds
Sub-surface Drainage Methods Fin & Narrow Filter Drain Drains the unbound pavement and formation Low capacity filter drains remove water: sub-base prevent softening Different types: HCDs 200 max 200 max 25 min Construction Granular material geotextile difficulties reported Height Core Core Backfill Minimum dig geotextile Perforated sock pipe (100 max) geotextile & trenchless techniques Pipe Pipe surround Pipe surround
SYSTEM OUTFALLS Discharge to watercourses directly via carrier pipes ▪ indirectly via flow attenuators ▪ - balancing ponds ▪ - detention tanks ▪ - vegetative treatment systems ▪ Discharge to ground soakaways Infiltration basins
What is Sustainable Drainage System (SUDS) (CIRIA 609 definition) ▪ The SUDS concept is to mimic, as closely as possible, natural drainage of a site in order to minimise the impact that urban development has on flooding and pollution of rivers, streams and other water bodies ▪ The use of a variety of techniques within the management train allows the SUDS concept to be applied to all sites. ▪ The techniques utilising vegetative features to treat pollution and slow down or reduce flows can enhance the landscape and provide wildlife habitat
The HE and SUDS The HE have been using SUDS for many years but now there is increased recognition of their role in; ▪ Pollution control and treatment (WFD) ▪ Flow attenuation and tackling effects of climate change (Making space for Water)
SUDS & SUDS Adoptable Systems ▪ Filter Drains ▪ Grassed Surface Water Channels ▪ Combined Grassed Channel and Filter Drain ▪ Wetlands ▪ Sediment Detention Ponds ▪ Sediment Detention Devices ▪ Reservoir Pavements ▪ Over-edge drainage (filter strip) ▪ Ditches
HE Business Needs SUDS have huge potential for pollution control but the HA would like a better understanding of; ▪ pollutant removal mechanisms and efficiencies ▪ optimum design parameters and retrofit solutions to maximise environmental performance ▪ space and fit often major design constraint – particularly with road widening and retro fit schemes ▪ benefits and disbenefits of combined treatment systems
The Water Framework Directive (WFD) The principal objectives set out in WFD Article 4 are: ▪ prevent the deterioration of the status of all surface and groundwater bodies; and ▪ protect enhance and restore all bodies of surface water and groundwater with the aim of achieving good surface water and groundwater status by 2015
Floods and Water management Act : 2010 This Act implements the recommendations from Sir Michel Pitt's Review of the floods in 2007 and places a series of responsibilities on the council. The main aim of the Act is to improve flood risk management . ▪ Appoints Lead Local Flood Authorities (LLFA) with a “Flood Risk management function” ▪ HE is a Designated Lead Flood Authority with the 'lead' role in managing flood risk from surface water, groundwater and ordinary watercourses across the county. This involves close working with partners involved in flood and water management, known as Risk Management Authorities. ▪ This Act legalise the need to incorporate SUDS into all future drainage designs and appoints SUDS approval bodies for approving designs ▪ HE is its own SUDS approval body and this is achieved by good upkeep and control of its Design Manuals for roads and Bridges (DMRB) – HD 50: The Certification of Drainage Design
Design Considerations HD 33: Surface & Sub-surface Drainage Systems for Highways Design Storm design for no surcharge1 in 1 year 1. check for no flooding of carriageway 1 in 5 year check for no flooding of external catchment 1 in 100 yr climate change 20% increase in rainfall intensity Catchment Run-off channel size outfall spacing Hydraulic adequacy pipe size gradient - self cleansing velocity = 1 m/s Structural adequacy traffic loading - 11.5 Tonnes wheel load Class D 400 (BS EN 124)
Water Quality Assessment & Flood Resilience HD 45 : Road Drainage and the Water Environment This standard gives guidance on the assessment and management of impacts that road projects may have on the water environment. These include possible impacts on the quality of water bodies and on the existing hydrology of the catchment through which road pass ▪ Provides tool for assessing water quality impact – HAWRAT (Highways England Water Risk Assessment Tool ▪ Design guidance on Pollution mitigation measures – Spillage Risk Assessment ▪ Design guidance on Flood Protection Measures
Climate Change ▪ The UK's climate is changing and these changes are expected to become more pronounced with continued global emissions of Green House Gases. ▪ The headline changes for the UK are warmer, wetter winters, and, hotter, drier summers. ▪ These climate change risks have been factored into our everyday considerations for maintenance, construction and operation of England’s strategic road network
Designing for Climate Change Planning Policy Statement PPS 25 - Dec 06 National Planning Policy Framework (NPPF) PPS 25 / NPPF - ‘Development and Flood Risk’ is now in effect ▪ ▪ HA (now HE) Strategy has since been revised in line with this policy, to accommodate climate change (an increase of 20 % in rainfall prediction) Extract from PPS 25
Main Changes – peak river flows From March 2016 CC Allowances published as NPPF 2016/17 Old PPS25 / NPPF HE – HD 45 to be revised to incorporate change ▪ The same predicted increase in ▪ Regional division of predicted increase in peak peak river flow for the whole of river flow based on river basin districts the country ▪ New percentiles of potential increases in peak river flow ▪ Increase differentiation between time periods
THE (HE) DRAINAGE STANDARDS Design and construction standards DMRB 4.2: Drainage Design Guidance DMRB 11.3: Road Drainage & the Water Environment MCHW : Manual of Contract Documents SHW -- 500 Series Specification HCD -- B & F Series Drawings MCHW 4 -- Method of Measurement MCHW 5 -- Specialist Activities • Section 8 -- Trenchless Installation • Section 9 -- CCTV Survey of Drainage
MAINTENANCE New Network Maintenance Manual and Routine & Winter Service Code (NMM & RWSC) - TRMM withdrawn Whole Life Cost based performance setting, and accommodating new drainage elements with varying asset life NMM & RWSC is still used on some legacy contracts but it is being systematically replaced by AMOR (Asset Management an Operational Requirement) introduced through the ASC • (Asset Support Contract) which will soon be fully replaced by the Cyclic and Reactive Maintenance Delivery Plan (CRMDP) introduced through the ADC (Asset Delivery Contract)
Asset Management HA43: Drainage Data Management System (DDMS) IAN 147: Drainage Data Management ▪ Identify and record the asset – Type – Location – Condition ▪ Manage maintenance efficiently ▪ Improve asset condition ▪ IAM IS:Integrated Asset Management Information System – Long-term plan is to subsume DDMS and all other asset databases into IAM IS
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