Micheál Mac Cárthaigh
Dublin Regional Inspectorate
Environmental Protection Agency
Richview, Dublin 14
Tel: (01) 268 0138
Fax: (01) 268 0199 email: m.maccarthaigh@epa.ie
August 2005
1

FLOODING IN THE DODDER CATCHMENT
Background
The River Dodder rises near Kippure in the Dublin Mountains. The principal tributaries of the River are the Rivers Owendoher and Slang. The full catchment area and the catchment areas of selected tributaries are given in Table 1 below.
River
Dodder
Owendoher
Slang
Dodder
Location
Station 09010 Waldron’s Br.
Station 09009 Willbrook Road
Station 09011 Frankfort
Confluence with the River Liffey
Catchment area (km²)
95.2
22.4
6.5
142.4
There are three other tributaries of the River Dodder: the Piperstown Stream, the Tallaght
Stream and the Little Dargle River. The Dodder Catchment is shown in Figure 1.
The River Dodder is dammed at Bohernabreena, about 13 km from Dublin. There are two impounding reservoirs at Bohernabreena in the catchment, the upper one of which is used to partly supply the needs of Dublin’s water supply and the lower one is used to control the compensation water in the river downstream of the impoundments.
In 2003, Dublin City Council commissioned a new spillway on the lower reservoir. For the duration of the construction of the new spillway, temporary works were constructed near the old spillway of the lower reservoir. The temporary spillway on the lower reservoir could not hold the floodwaters of the flood that occurred on 2/12/2003.
The River Dodder joins the River Liffey in Dublin City.
Hydrometric Data
Hydrometric data has been collected at a number of hydrometric stations in the Dodder
Catchment as follows:
The then Dublin Corporation (now Dublin City Council) installed an OTT water level recorder in the River Dodder at Station 09010 Waldron’s Bridge in 1952. The Irish grid reference of the location of the station is O 156 297. Dublin City Council upgraded the recording equipment to an OTT Thalimedes data logger on 18 October 2000. Dublin
City Council proposes to have this station on-line in the near future. The EPA hopes to be able to access this data on-line.
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The then Dublin County Council (now South Dublin County Council) erected a recorder on the River Owendoher at Station 09009 Willbrook Road in November 1980. The Irish grid reference of the location of the station is O 142 285. A channel control was erected at the station on 1 October 1996. South Dublin County Council upgraded the recording equipment to an OTT Thalimedes data logger on 22 March 2002.
The then Dublin County Council (now South Dublin County Council) erected a recorder on the River Slang at Station 09011 Frankfort in May 1982. The Irish grid reference of the location of the station is O 169 288. A channel control was constructed at the station completed on 14 August 1986. South Dublin County Council upgraded the recording equipment to an OTT Thalimedes data logger on 26 March 2002.
At all three hydrometric stations, the EPA undertakes calibration flow measurements to calibrate the relationship between water level and rate of flow. Dublin City Council and
South Dublin County Council changed the OTT charts, respectively, on a weekly basis.
The EPA processed the charts, as detailed below. With the advent of data loggers, EPA staff download the data loggers. The EPA processes the data into a format suitable for the local authorities.
South Dublin County Council recently (June 2005) erected a channel control in the River
Dodder at Bohernabreena and proposes to erect a Thalimedes data logger at this location.
It is proposed that this station will be on-line.
Reports of Previous Flooding in the River Dodder
The then Dublin Corporation has indicated that, during a spate in the River Dodder, which takes about 20/24 hours to come to peak, the recorder was invaluable in assessing what stage the flood has reached and what action or flood prevention work, if any, may immediately be necessary.
In a paper read to the Old Dublin Society on “Weather in Old Dublin” by F. G. Dixon, reference is made to floods on the River Dodder in September 1787, November 1794,
December 1802 (“this must rank as the most serious of all Dublin Floods”), September
1807 and January 1851. The construction of the reservoir system at Bohernabreena in
1883, to serve as a water supply to the City of Dublin, has helped to alleviate downstream flooding.
In the paper by Jack Keyes (Keyes, J. IEI, 16 November 1987), reference is made to previous floods in the Dodder catchment in the period 1880-1986. The peak flowrates estimated at Bohernabreena and at Orwell Bridge (Station 09010 Waldron’s Bridge) are provided after each date (where available) in Table 2:
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Date
25 August 1986
25 August 1905
03 September 1931
19 October 1891
17 November 1965
19 December 1958
12 August 1946
02 November 1968
26 August 1912
16 October 1883
25 September 1957
29 September 1956
Bohernabreena m³/s
91
99-118
?
96
65
57
79
?
65
48
42
30
Orwell m³/s
215-254
198
153
?
139
116
88
85
?
?
74
73
________________________________________________________________________
Comparison with Previous Flooding in the Tolka Catchment
Records available from Dublin City Council indicate that there was previously flooding in the Tolka Catchment on 28 October 1880, 23 November 1898, 12 November 1901, 12
November 1915, 3 September 1931 and 20 September 1946.
In the flooding which occurred on 8/9 December 1954, a peak flood of 85 m³/s was estimated to have occurred at the weir upstream of Finglas Bridge.
The peak flow recorded at Station 09019 Drumcondra on the River Tolka in the flood of
25 November 1965 corresponded to a flow of 59.5 m³/s.
A flood recorded at Station 09019 Drumcondra on the River Tolka on 25 December 1968 had a peak flow estimated at 45-48 m³/s.
Ratings
The ratings have been developed by the EPA at each of the three hydrometric stations in the catchment as follows:
Station 09010 Waldron’s Br. 107 m³/s
Station 09009 Willbrook Road 6 m³/s
Station 09011 Frankfort 2 m³/s
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Flowrates quoted in excess of these values are based on extrapolation of the rating curve and should be treated with caution.
Hydrograph of Water Level and Flow for the Period of Record
In Appendix 1, the following hydrographs for the period of record are presented:
1. Hydrograph of (1) water level and (2) flow at Station 09010 Waldron’s Bridge on the
River Dodder for the period 2 January 1986-July 2005.
2. Hydrograph of (1) water level and (2) flow at Station 09009 Willbrook Road on the
Owendoher River for the period 18 November 1980-July 2005.
3. Hydrograph of (1) water level and (2) flow at Station 09011 Frankfort on the River
Slang for the period 5 May 1982-July 2005.
The peak water levels and flowrates at Station 09010 Waldron’s Bridge on the River
Dodder in the period of record are presented in the Table 3.
Activity during the Flood on 25/26 August 1986 (Hurricane Charlie)
A full report on the activities of all the statutory agencies during the Hurricane Charlie flood was given to a meeting of the Water Engineering Section of the Institution of
Engineers of Ireland (IEI) (Volume 12. Transactions 1987/1988) (see list of references).
The hurricane of 25/26 August 1986 travelled from the South West of Ireland to the
South East coast and then proceeded along the East coast as far as Kippure Mountain in
County Wicklow. The hurricane then proceeded to Wales.
In the Greater Dublin area, there was severe flooding in the Avoca, Dargle and Dodder
Catchments with large numbers of houses flooded. Interestingly, in the Liffey
Catchment, the Pollaphouca Reservoir was able to contain the floodwaters of the flood in that catchment.
The Rivers Aughrim, Avonmore, Dargle, Dodder, Owendoher and Slang were in full spate.
The hydrographs of water level and flow for the Hurricane Charlie flood at hydrometric stations on the Rivers Dodder, Owendoher and Slang are presented in Appendix 2.
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Annual Maximum Peak Water Levels and Flows
Station 09010 Waldron's Bridge
Hydrometric year Date
River Dodder
Time
From To Hrs
1-Oct-85 30-Sep-86 26-08-1986 02:00:00
Peak water Flowrate level m
3.02 m³/s
269 Hurricane Charlie
1-Oct-86 30-Sep-87 05-04-1987 04:04:00
1-Oct-87 30-Sep-88 21-10-1987 17:52:00
1-Oct-88 30-Sep-89 01-10-1988 00:00:00
1-Oct-89 30-Sep-90 19-02-1990 17:45:00
1-Oct-90 30-Sep-91 12-04-1991 13:32:00
1-Oct-91 30-Sep-92 03-07-1992 21:21:00
1-Oct-92 30-Sep-93 11-06-1993 18:00:00
1-Oct-93 30-Sep-94 03-02-1994 23:16:00
1-Oct-94 30-Sep-95 27-01-1995 19:32:00
1-Oct-95 30-Sep-96 06-01-1996 18:31:00
1-Oct-96 30-Sep-97 11-06-1997 08:47:00
1-Oct-97 30-Sep-98 09-04-1998 07:03:00
1-Oct-98 30-Sep-99 30-12-1998 01:58:00
1-Oct-99 30-Sep-00 25-04-2000 14:15:00
1-Oct-00 30-Sep-01 05-11-2000 23:00:00
1-Oct-01 30-Sep-02 07-10-2001 22:15:00
1-Oct-02 30-Sep-03 14-11-2002 17:45:00
1-Oct-03 30-Sep-04 02-12-2003 08:45:00
1-Oct-04 30-Sep-05 29-10-2004 06:00:00
1.253
0.903
---
---
---
---
1.418
1.665
0.926
1.066
0.68
1.468
1.063
0.902
2.173
0.971
1.201
1.78
1.266
64
33
---
---
---
---
81
110
35
46
18
87
46
33
156
41
58
112
64 available charts
1/1/1986 to
31-12-1987 available charts from 1/1/1990 latest data logger download
12-07-2005
The EPA is agreeable to assess the charts for the periods (1) 1952-1985 and (2) 1988-
1989 with a view to processing them. Hydrographs of level and/or flow for individual flood events can be made available.
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Activity on 2 December 2003
On 2 December 2003, a flood occurred in the Dodder Catchment and data was sought on this flood from the EPA.
Following reports of flooding in the River Dodder on the morning of 2 December 2003, the EPA Dublin regional hydrometric team checked the hydrometric stations on the
Rivers Slang, Owendoher and Dodder.
The Rivers Slang and Owendoher were in a moderate flood but the River Dodder was in full spate.
Flood of 2 December 2003
The flood hydrographs for the flood that occurred on 2 December 2003 are presented in
Appendix 3.
Station 09010 Waldron’s Br. on the River Dodder
At 3:30 hrs on 2 December 2003, the water level started to rise. The water level rose steadily until 7:15 hrs on 2 December 2003. It then rose steeply until a level of 1.78 m was recorded at 8:45 hrs on 2 December 2003. The flowrate corresponding to this level of 1.78 m is estimated at 112 m³/s. The water level dropped off until pre-flood water levels were recorded in the River Dodder.
Station 09009 Willbrook Road on the River Owendoher
At 01:15 hrs on 2 December 2003, the water level started to rise steadily until a peak water level of 0.79 m was recorded at 07:45 hrs on 2 December 2003. There was then a steady decline in water levels. The flow rate corresponding to this peak water level of
0.79 m is estimated at 9.9 m³/s.
Station 09011 Frankfort on the River Slang
At 20:45 hrs on 1 December 2003, the water level started to rise. There was a small flood hydrograph, which peaked at 22:30 hrs on 1 December 2003. Water levels then declined until 2 December 2003 at 1:00 hrs. The water level then rose in two steps, until 2
December at 3:15 hrs, then to 2 December at 05:15 hrs and then peaked at a level of 0.60 m at 06:45 hrs on 2 December 2003. This level of 0.6 m corresponds to a flow of 0.87 m³/s.
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References
Barry, Des (J. B. Barry & Partners). Hurricane Charlie – River Dargle”. A paper presented to the Water Engineering Section, IEI, 16 November 1987.
Dixon, F. G. “Weather in Old Dublin”. F. R. Met. Soc. Vol. 13, 1953. Old Dublin
Society.
Doyle, E. (Wicklow County Council). Hurricane Charlie – An Overview”. A paper presented to the Water Engineering Section, IEI, 16 November 1987.
Hennigan, P., McDaid, J., Keyes, J., (Dublin County Council and Dublin Corporation) .
“Dodder River – Flood Study”. A paper presented to the Civil Division, IEI, November
1988.
Joyce, T. (Office of Public Works). “Hurricane Charlie – An Overview”. A paper presented to the Water Engineering Section, IEI, 16 November 1987.
Keyes, J. (Dublin Corporation). “Hurricane Charlie – An Overview- Flooding in Dublin
City Rivers - 25/26 August 1986”. A paper presented to the Water Engineering Section,
IEI, 16 November 1987.
Keyes, J. (Dublin Corporation). “Hurricane Charlie – River Dodder Flooding”. The
Engineers Journal Vol. 40, Number 11. November 1987.
MacCárthaigh, M. (An Foras Forbartha). “Hurricane Charlie – An Overview - The activities of An Foras Forbartha”. A paper presented to the Water Engineering Section,
IEI, 16 November 1987.
McDaid, J. (Dublin County Council). “ Hurricane Charlie – An overview- An Analysis on the River Dodder”. A paper presented to the Water Engineering Section, IEI, 16
November 1987.
O’Reilly, G. (Meteorological Service). “Storm of 25/26 August 1986 which caused flooding in the Dargle Catchment (Bray) and Dodder Catchment (Dublin)”. A paper presented to the Water Engineering Section, IEI, 16 November 1987.
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Reconsructed hydrograph of Water Level at Station 09011 Waldron’s Br.
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