Urban Pathways and Pressures

John Stack, Executive Engineer Dublin City Council

‘Urbanisation’

“The process by which towns and cities are formed and become larger as more and more people begin living and working in central areas”

• ∼ 40% of Irish population lives in Greater Dublin Area

• ∼ 527,000 people living in city • ∼ 80% of surface area is impervious

Urbanisation

Impact of Urbanisation on Water Cycle

• Urbanisation has fundamentally altered the way that water moves through the landscape.

• Increasing Impervious Surface Area: – Prevents groundwater recharge from rainfall, which – Reduces baseflow in rivers as they are no longer

adequately fed by groundwater – Increases frequency and severity of floods due to

greater surface runoff – Causes pollution of surface waters

Urban Pathways

• Vast majority of urban pollutants enter waters via a pipe – Foul/combined drainage network – Surface/Storm water drainage network – Private drains

• Groundwater

Drainage Infrastructure as a pathway

• ∼2,000 km of sewer – ∼ 660 km foul – ∼ 541 km combined – ∼ 788 km surface/storm

• 39 pumping stations • 212 combined sewer overflows • Largest wastewater treatment plant in Ireland • ∼ 54,500 road gullies (± 500) • 39 underground rivers

Dublin City Drainage

Pressures

• Classification: – Via foul/combined drainage infrastructure – Via surface/storm water drainage infrastructure – Direct to water

• Further classification – Acute: short term, infrequent – Chronic: continuous

Pressure Description Impacts on Acute/ Chronic Upstream pressures Pressures in upstream catchments impact on water quality

entering into DCC functional area All water bodies Both

Foul Drainage Network • Network capacity issues • Effects of combined sewer overflow spil lages – spil lages

from foul/combined sewer network to waters as a result of rainfall

• Sewer chokes (impacts all water bodies) • WWTP (Liffey Estuary and Dublin Bay) • Exfiltration due to infrastructural deficiencies

All water bodies (WWTP relates only to Liffey Estuary Lower and Dublin Bay)

Both

Misconnections Discharges from household appliances and toilets to the surface water network

All water bodies outside combined area

Chronic

Urban Runoff • Road runoff • Runoff from other hardstanding areas

o Car Parks o Cobblelocked driveways o Roofs

• Il legal disposal of polluting matter to gull ies (e.g. old engine oil, etc.)

• Cross connections from foul to surface water network (both public and private)

• Animal/bird faeces • Private drain blockages • Car washing on kerbside/in driveways • Discharges not subject to l icence (e.g. business/people

washing shop/house fronts and floors and throwing the washwater into the gull ies

• Unlicensed discharges

All water bodies outside combined area

Chronic

Historical changes to morphology • Lots of reclaimed land in the region • River channels altered, culverted, canalised, diverted Leads to increase flowthrough, loss of riparian zones and natural river features (impacts all water bodies)

All water bodies Chronic

Historical landfills A number of historical landfills may be impacting on some rivers Liffey, Tolka, Santry Chronic

Foul Drainage Network

CSO Spill Date E coli

(MPN/100 ml)

Ammonia (mg/l N)

Phosphorus (mg/l P)

21/7/2011 129,970 11 1

Pipe φ 0.6 m

Pipe flow 33 l/s Manning’s equation

Load 43 million MPN/s

363 ml/s 33 mg/s

For 10 hour spill

1.5 Trillion MPN

13 kg 1.2 kg

Rainfall for July 2011

Monthly rainfall, July 2011 % of 1961 – 1990 average No. days rain during month (> 1 mm)

38.1 mm 88% 10

Perception that CSO discharges are heavily diluted – they’re not

Illegal Dumping??

Misconnections Appliance BOD (mg/l) pH Suspended Solids

(mg/l) Phosphorus (mg/l) Population Equivalent

Washing Machine Flow (l itres) Required Dilutions

1,534 58.5

17,948

10 366 0.53 1.50

Dishwasher Flow (l itres) Required Dilutions

313 25.0

1,565

9.2 19 0.32 0.13

Car Wash* Flow (l itres) Required Dilutions

3,160 7.0

4,424

- - - 0.36

Washing Machine BOD P

Concentration 1,534 mg/l 0.53 mg/l

@ 60 litres 92,040 mg 31.8 mg

4 washes/week 208 washes/year 208 washes/year

Annual Load/miscon

19.1 kg/year 0.0066 kg/year

3,168 miscons* 60, 649 kg/year 21 kg/year

Annual PE > 1 million

* Assume 60% of misconnections are washing machines

Car Washing

Specification Karcher K2

Hose length 4 metres

Motor power 1.4 kw

Actual Bar Rated Pressure

110 Bar Max Water Pressure

Flow Rate Max 360 litres/hr

Estimated Annual PE from car washing

BOD 3,160 mg/l

Assume 10% of householders wash cars fortnightly

6,600 washes/fn

Wash takes 20 minutes 120 litres

BOD kg/fortnight 2,502 kg/fn

BOD kg/year 65,070 kg/year

Annual PE > 1 million

Car Wash – backstreet garage

Historical landfills

Morphological Changes

Heavily Modified Water Body

Urban Runoff

• Storm/Rainfall runoff created by urbanisation • Major source of flooding • Major source of water pollution • Urban runoff is typically untreated

Urban v Rural

Research: Nationwide Urban Runoff Programme (USEPA, 1979 – 1983)

• Study objectives: – Assess the water quality impact of urban runoff

across a number of cities – Assess the impact of urban runoff on overall water

quality – Implement storm water management best

practices.

NURP Findings • Heavy metals (especially copper, zinc and lead) are the most prevalent priority

pollutant substances found in urban runoff • Coliform bacteria are present at high levels in urban runoff • Nutrients are generally present in urban runoff but, in general, concentrations are

not high compared to other sources • Oxygen demanding substances are present in urban runoff at concentrations

approximating those in secondary treatment plant discharges • The physical aspects of urban runoff (i.e. erosion and scour) can be a significant

cause of habitat disruption and can affect the type of fish present • Detention basins and recharge devices are capable of providing very effective

removal of pollutants in urban runoff • Wet basins (a design which maintains a permanent water pool) have the greatest

performance capabilities • Wetlands are considered to be a promising technique for control of urban runoff • Interestingly, the NURP found that street sweeping was ‘ineffective as a technique

for improving the quality of urban runoff’.

Our findings – monitoring during rainfall event

Date: 21st July 2011 Ammonia B.O.D. Dissolved

Oxygen Dissolved Oxygen

E. coli Nitrate Nitrite Phosphorus (React)

Suspended Solids

TON

Number of Locations = 25

mg/l as N

mg/l

% Sat.

mg/l

MPN/ 100ml

mg/l as N

mg/l as N

mg/l as P

mg/l

mg/l as N

Average

0.96

17.89

92.80

9.30

13286.25

0.65

0.04

0.24

125.05

0.69

Max

11.08

154.00

99.00

10.00

129970.00

1.54

0.09

1.01

415.00

1.60

Median

0.22

8.00

94.00

9.40

5803.00

0.51

0.04

0.10

119.50

0.52

Examples of Urban Runoff

Traffic

3 km slick

Birds

LOTS of birds

NPWS = approx 13,000 birds in South Dublin Bay

Horses and other animals

This??

Construction

Cobblelock

Ave. 26m2

132,000 houses in Dublin If 20% of these convert front garden to cobblelock, that’s 686,400 m2 new impervious area x 2.54 cm (1”) of rainfall = approx. 17,500 m3 additional runoff

Private Drain Blockage

Blocked drains = big business

It’s not just Dublin and it’s not static

Urban Creep,…or crawl perhaps

Urban centres Population density >10,000 >20,000 >50,000

Leinster 25 14 2

Munster 13 4 2

Connaught 4 2 1

Ulster* 2 0 0

*ROI counties only

Surface Area of Major Towns/Cities Surface Area (km2) Potential Impervious Area

(km2)

Cork 37 29

Dublin 114 91

Limerick 51 41

Galway 53 42

Waterford 41 35

Housing Agency’s National Statement of Housing Supply and Demand

New Housing requirements to 2020 City/Town Demand

Dublin Min 33,000

Cork 8,434

Limerick 3,436

Galway 2,316

Waterford 713

10 other towns >800

> 30 town > 300

Ireland to 2040

“…unmanageable sprawl of housing areas, scattered employment and car based commuting, presenting…adverse impacts on peoples’ lives and the environment.”

Summary • Urban environment extremely complex • Very broad range of pressures

– Difficult to classify – Difficult to quantify

• Urban runoff has a serious negative impact on water quality

• No quick fixes or easy solutions • Solutions will require creativity, investment,

community engagement, boots on the ground and time