Let's Do Some Calculations: How Much Water?

© Eugene Brennan

I know I'm getting nerdy about this and becoming somewhat obsessed, but let's do some calculations for the total amount of water which has been flowing through the town per day.

Releases of water from Golden Falls dam in Ballymore Eustace have been unusually high over the last week. Some of this water will have flowed through the penstocks (large diameter pipes) to power the alternator and generate electricity. If power from the hydroelectric station can't be accepted by the grid and water level is too high in the lake supplying the dam, it has to "overflow". It's released through "doors" known as sluices, which are raised by electric motors. It then flows down concrete spillways into the river. Flow rate can typically be up to 15 or 20 cubic metres per second (m³/s) during extended periods of rainfall, but over the last couple of days, the rate has peaked at 33 m³/s for periods during the mornings. The ESB provides hydrometric information on their website for several hydro power stations throughout the country. This information consists of head race levels in reservoirs feeding the dams, average daily flow rates and a single set of flow rate figures, which represent projected values at eight-hour intervals throughout the day. At the Golden Falls dam in Ballymore Eustace, average daily flow since 12th December has been 25 m³/s. That's a per second flow rate, but averaged over a whole day. So at times, it was higher than this and lower at other times. For instance, for Thursday 18th December, flow rates were forecast at 20.0, 33.0, 20.0 and 20.0 m³/s, at 00:00 (midnight), 08:00, 16:00 and 00:00 (midnight the next day) respectively.

So to calculate the quantity of water that has been passing through the town over a 24 hour period, simply multiply the flow rate per second by the number of seconds in a day:

Total flow in 24 hours = average flow rate in m³/s x number of seconds in a day

= 25 x 60 x 60 x 24

= 2,160,000 m³

To put that into perspective, it's the volume occupied by a cube with sides 129 m long; the distance from the crossroads in the town centre to Bardon's pub. 

Related Reading

Golden Falls Generator Assembly 

Golden Falls Dam and Ballymore 5 km Loop 

Golden Falls dam in Ballymore Eustace. © Eugene Brennan