Peacock Gap flood risk problems

Surface Water Drains Heights

The developers propose raising ground level by 3 meters in the eastern corner of the site.

A 0.6m timber retaining wall is shown. Timber has a limited life, typically shorter than the expected life of the proposed

homes and associated drainage system.

The site presently slopes steeply, however at the proposed location of the surface water storage tank the slope will be further

increased so that ground stability problems will put the proposed surface water storage tank at risk.

Details of the surface water drainage show invert levels higher than finished floor levels. The outside areas including the roads

will flood the houses as the surface water drains as shown are higher than the finished floor levels.

As the cover level of the drains is higher than the finished floor levels, and the associated roads, the roads will not drain into

the proposed storage tank.

No detail of the road drainage hardware is adequately given. The site is steeply sloping. Surface water passes over gullies

when heavy rainfall occurs so that beany blocks should be used in order to ensure that surface water is captured by the

drainage system and that flood attenuation proposed as being given by the proposed limited outflow storage tank does

actually function as required to prevent an increase of downstream flood risk for residents subject to flooding from the Cotting

Burn.

Rainfall

The rainfall figure used by the developer’s consultants is 700 mm of annual rainfall.

Four sets of locally collected rainfall over the last twenty years produce an average annual rainfall figure of 805 mm.

This data is collected by three local residents and Newcastle University.

Drainage systems designed on the basis of rainfall figures 105 mm below the actual twenty year average will be too small.

Flooding will increase if these local figures are ignored.

Drainage System Maintenance

Frequent maintenance of the proposed drainage system will be necessary as there are trees in the area and potential

homeowners typically plant additional shrubs and trees which will add to the drain maintenance load.

Metal grid drains are unable to accept leaves and become blocked with small amounts of leaf litter. Drains maintenance

requirements must be planned for sustainability. Beany blocks must be used in order to ensure that drains can be maintained

at sustainable intervals.

Morpeth town centre is served by the same Northumberland County Council maintenance team and equipment. Substantial

additional funds must be put in place for maintenance of outlying areas which drain down roads into the town centre if flood

risk, which is presently unsustainably high, is not to further increase down the hill in the town centre.

Whorral Bank drains blocked and road reduced to single carriageway. This occurs so frequently that the road to the right has

been damaged by surface water.

The Dell drains do not presently receive adequate maintenance so that residents must get their drain rods out and clear them.

This cannot be allowed to continue as residents are not able to respond to these problems adequately.

Castle Bank brings surface water into the town center which floods Middle Greens.

Northumberland County Council charges residents but fails to provide adequate highway drainage and the maintenance

service is unable to remedy inherently inadequate drains. The impact on residents is obvious.

Northumbrian Water Sewers

The manhole beneath the Chantry footbridge overflows during periods of rainfall lifting the manhole cover.

Following an overflow the River Wansbeck can flow into the sewer system depending on river levels.

The manhole cover has been changed however it is not entirely self closing and continues to spill untreated, unscreened,

undiluted sewage onto the bank of the River Wansbeck and directly into the river in the town centre.

Original overflow pipe.

The original sewer overflow was blocked off in an attempt to prevent this pollution. The pollution continues.

Dry weather flow in this sewer is approximately 50% of capacity. This is a combined sewer draining surface water from the

connected areas in addition to foul sewage. The sewer is overloaded.

The sewer flows from Carlisle View shown in the above plan, draining the area’s foul and surface sewage.

It also receives sewage and surface water from High Stanners, Dogger Bank and Mitford Road.

When the sewer system is loaded above capacity it overflows into Staithes Lane. Homes were externally flooded by sewage on

14th November 2014. This was during a period of rainfall which the system should be capable of handling. It is not.

18 mm. of rain fell over a period of 7 1/2 hours. This rainfall data was recorded by two independent local residents.

The arrow above indicates the Salisbury Street chamber which receives all of Morpeth’s sewage which flows to the sewage

treatment works on Parish Haugh.

The Salisbury Street / Gladstone Street chamber overflows frequently, discharging raw sewage into food crops and leaving

litter and sewage on local roads.

2012 Salisbury Street / Gladstone Street sewer chamber overflow.

Food crops growing on Parish Haugh are polluted by the sewage spills.

Leeks

and turnips received the 2013 sewage spill.

July 2013 sewage spill.

Following the 14th November 2014 heavy rainfall.

The consequence of adding more load to the existing Northumbrian Water sewer system serving the whole of Morpeth will be

more frequent repeats of unacceptably frequent pollution incidents.

The permission from Northumbrian Water to the developer to discharge sewage from the proposed Peacock Gap

development was for a one year period which is now passed.

That permission should never have been granted given the overloaded condition of the downstream sewer network but has

now lapsed.

Any new developments in the town must be connected directly to the Parish Haugh sewage treatment works, bypassing the

legacy overloaded sewer network.

The pictures illustrate the Staithes Lane problem, however homes in High Stanners were flooded by sewage in 2012 and

Carlisle View homes remain vulnerable to sewage surcharges.

Conclusion

Morpeth Flood Action Group objects to the proposed Peacock Gap development on grounds of downstream flood risk from

the Northumbrian Water combined sewer system, and surface water flood risk in The Dell.

The designed capacity of the proposed surface water storage tank is inadequate as rainfall figures used are too low which puts

town centre homes subject to flooding from the Cotting Burn at increased risk of flooding.

We ask for conditions to be applied so that:-

1. Foul sewage from the development must be taken directly to the sewage treatment works via a new sewer bypassing

the existing overloaded town centre sewage network.

2. Surface water storage and drainage systems must be designed to produce acceptable flood risk by using annual

rainfall figures of at least 805 mm..