This presentation was given at the Catchment Management Network meeting on February 24th 2017. The Catchment Management Network consists of the EPA, all of Ireland's Local Authorities, and other public bodies involved in looking after Ireland's catchments, sub-catchments and water bodies. For more information about this work see www.catchments.ie

1. Urban Pathways and Pressures
John Stack, Executive Engineer
Dublin City Council

2. ‘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 populationlives in Greater
Dublin Area
• ∼ 527,000 people living in city
• ∼ 80% of surface area is impervious

3. Urbanisation

4. 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

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

6. 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

7. Dublin City Drainage

8. Pressures
• Classification:
– Via foul/combined drainage infrastructure
– Via surface/storm water drainage infrastructure
– Direct to water
• Further classification
– Acute: short term, infrequent
– Chronic: continuous

9. Pressure Description Impacts on Acute/ Chronic
Upstream pressures Pressures in upstreamcatchments impacton water quality
entering into DCC functional area
All water bodies Both
Foul DrainageNetwork • Network capacity issues
• Effects of combined sewer overflow spillages –spillages
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 dueto infrastructural deficiencies
All water bodies (WWTP
relates only to Liffey
Estuary Lower and Dublin
Bay)
Both
Misconnections Discharges fromhousehold appliancesand toilets to the surface
water network
All water bodies outside
combined area
Chronic
Urban Runoff • Road runoff
• Runoff from other hardstandingareas
o Car Parks
o Cobblelocked driveways
o Roofs
• Illegal disposal of pollutingmatter to gullies (e.g. old
engine oil,etc.)
• Cross connections fromfoul to surfacewater network
(both public and private)
• Animal/bird faeces
• Privatedrain blockages
• Car washingon kerbside/in driveways
• Discharges notsubjectto licence(e.g. business/people
washingshop/housefronts and floors and throwingthe
washwater into the gullies
• 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 increaseflowthrough, loss of riparian zones and natural
river features (impacts all water bodies)
All water bodies Chronic
Historical landfills A number of historical landfillsmay be impactingon some rivers Liffey, Tolka,Santry Chronic

10. Foul Drainage Network

11. 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 areheavily diluted – they’renot

12. Illegal Dumping??

13. Misconnections
Appliance BOD (mg/l) pH Suspended Solids
(mg/l)
Phosphorus (mg/l) Population Equivalent
WashingMachine
Flow (litres)
Required Dilutions
1,534
58.5
17,948
10 366 0.53 1.50
Dishwasher
Flow (litres)
Required Dilutions
313
25.0
1,565
9.2 19 0.32 0.13
Car Wash*
Flow (litres)
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 arewashingmachines

14. 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

15. Car Wash – backstreet garage

16. Historical landfills

17. Morphological Changes

18. Heavily Modified Water Body

19. Urban Runoff
• Storm/Rainfallrunoff created by urbanisation
• Major source of flooding
• Major source of water pollution
• Urban runoff is typically untreated

20. Urban v Rural

21. 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.

22. NURP Findings
• Heavy metals (especially copper, zinc and lead) are the most prevalentpriority
pollutantsubstances found in urban runoff
• Coliform bacteria are present at high levels in urban runoff
• Nutrients are generally present in urban runoff but, in general, concentrationsare
not high compared to other sources
• Oxygen demanding substances are present in urban runoff at concentrations
approximatingthose in secondary treatment plant discharges
• The physicalaspects of urban runoff (i.e. erosion and scour) can be a significant
cause of habitatdisruption and can affect the type of fish present
• Detentionbasins and recharge devices are capableof providingvery effective
removal of pollutantsin urban runoff
• Wet basins (a design which maintainsa permanent water pool) havethe greatest
performance capabilities
• Wetlands are consideredto be a promising techniquefor controlof urban runoff
• Interestingly, the NURP found that street sweeping was ‘ineffective as a technique
for improving the qualityof urban runoff’.

23. 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

24. Examples of Urban Runoff

25. Traffic
3 km slick

26. Birds

27. LOTS of birds
NPWS = approx 13,000 birds in South
DublinBay

28. Horses and other animals

29. This??

30. Construction

32. 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

33. Private Drain Blockage

34. Blocked drains = big business

35. It’s not just Dublin and it’s not static
Urban Creep,…or crawl
perhaps

36. 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

37. 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

38. 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

39. Ireland to 2040
“…unmanageable
sprawl of housing areas,
scattered employment
and car based
commuting,
presenting…adverse
impacts on peoples’
lives and the
environment.”

40. 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