Drainage and Water

HA0328-049 Water is vital for all liv­ing plants and ani­mals.  For human beings it is not only essen­tial to life but also of cru­cial impor­tance in indus­try and agri­cul­ture, as a means of trans­port and for recre­ation.  Water which runs off roads can poten­tially have an impact on the qual­ity of receiv­ing sur­face waters and ground­wa­ter and/or influ­ence the occur­rence of local flooding.

Deal­ing with Water Qual­ity and Flood Risk within the High­ways Agency

The High­ways Agency has sole respon­si­bil­ity and pow­ers for man­ag­ing the quan­tity and qual­ity of road runoff that is col­lected within the High­ways Agency Net­work. This means that the Agency must ensure that;

  • Road projects do not increase flood risk.
  • High­way dis­charges do not pol­lute receiv­ing water bodies.

In meet­ing these require­ments the HA has devel­oped envi­ron­men­tal assess­ment tools and pol­icy guid­ance, in con­sul­ta­tion with the Envi­ron­ment Agency, for flood risk and pol­lu­tion risk for road projects. Within each pro­posed High­ways Agency project the water envi­ron­ment is con­sid­ered within the envi­ron­men­tal impact assess­ment (EIA). Where a poten­tial pol­lu­tion and/or flood risk is iden­ti­fied as part of an EIA this is used to inform the drainage design in order that any risks are appro­pri­ately managed.

In sup­port of its statu­tory duties the High­ways Agency con­tin­ues to iden­tify and imple­ment prac­ti­cal steps to man­age the risks to the water envi­ron­ment from the road net­work in response to Gov­ern­ment pol­icy and improved knowl­edge. In par­tic­u­lar the HA has a for­ward pro­gramme of works aimed at installing treat­ment or con­tain­ment mea­sures at exist­ing out­fall sites that have been iden­ti­fied as pos­ing a poten­tial pol­lu­tion risk. Sim­i­lar pro­grammes of work are being devel­oped for dis­charges to ground and loca­tions vul­ner­a­ble to flooding.

Road Drainage

Well designed and well main­tained road drainage is impor­tant in order to:

  • Min­imise the envi­ron­men­tal impact of road runoff on the receiv­ing water environment
  • Ensure the speedy removal of sur­face water to enhance safety and min­imise dis­rup­tion to road users.
  • Max­imise the longevity of the road sur­face and asso­ci­ated infrastructures

There are many dif­fer­ent types of drainage sys­tems with dif­fer­ent design fea­tures and attrib­utes that can be used to man­age flows and treat water qual­ity. Drainage which is needed on the High­ways Agency net­work depends not just on any flood risks and pol­lu­tion risks iden­ti­fied but the char­ac­ter­is­tics of the nat­ural water catch­ment area in which the net­work is based. The size, shape, gra­di­ent and geol­ogy of a catch­ment area are all fac­tors which can influ­ence the type of drainage meth­ods used.

Older roads tend not to have the more devel­oped drainage sys­tems. New roads are now designed to include drainage sys­tems intended to chan­nel and man­age the flows of excess water from the net­work to pre­vent flood­ing as well as pro­vide pol­lu­tion treat­ment.  The High­ways Agency has for many years used Sus­tain­able Drainage Sys­tems (SUDS) on its road net­work. Not all SUDS how­ever are suit­able for use on the HA’s road net­work and the HA has devel­oped guid­ance on selec­tion design, con­struc­tion and main­te­nance of those drainage sys­tems that are used on its network.

Some of the dif­fer­ent drainage meth­ods used on the High­ways Agency net­work include:

  • Soak­aways
  • Bal­anc­ing ponds
  • Sur­face flow wetlands
  • Grassed sur­face water channels
  • Fil­ter drains
  • Sur­face water channels
  • Kerbs and gullies

To ensure block­ages are pre­vented and sys­tems per­form effec­tively a main­te­nance regime is required that is appro­pri­ate for the type of sys­tems in use.

Mem­o­ran­dum of Under­stand­ing with the Envi­ron­ment Agency

The High­ways Agency devel­ops strate­gic part­ner­ships with other organ­i­sa­tions to help improve co-operation, to share infor­ma­tion and strat­egy, and to sup­port each oth­ers objec­tives. In line with this approach we have estab­lished a Mem­o­ran­dum of Under­stand­ing (MOU) with the Envi­ron­ment Agency to sup­port effec­tive work­ing between the two Agencies.