Rivers in Ireland

freighter

I hope this is the correct place for this.

As you all know we are having a long hot spell at the moment. The thing that confuses me is that it has not rained in weeks now and local rivers are still flowing away.

The Blackwater beside me still has a good flow and so has its tributaries. How is this when their is no rain falling. Where is the water coming from????. If it stays hotter for longer will these rivers stay flowing for long or dry up.

Sorry for the silly questions:o:o

delta_bravo

freighter wrote: »

I hope this is the correct place for this.

As you all know we are having a long hot spell at the moment. The thing that confuses me is that it has not rained in weeks now and local rivers are still flowing away.

Weeks? I think you are overexaggerating a bit. There were some heavy rainfalls in parts a week to 10 days ago. Rain occurs more where rivers are at their source plus rainfall is not their only source. There are a number of other sources such as underwater tributaries, transpiration etc. Its not all about precipitation!

El Siglo

OP, this is Ireland not Australia.:D
River flow is usually derived from groundwater inputs as an influent from the unconfined aquifer. Whenever it rains, most water infiltrates soil and will move with the gradient of the surface (water moves through the soil), too much infiltration and you get surface wash (think of puddle of water on a football pitch). So really, even if it hasn't rained in a long time, and it usually takes a long time for a river to 'dry up', it will generally still have groundwater inputs. And you'd also have to take into account, osmotic pressure (i.e. water will move from areas of high water pressure to low water pressure) this coupled with hydrostatic forces (H2O molecules attract but don't bond to one another) along with gravitational forces will all more or less cause the water to move to a surface stream or an area of equally lower water pressure.
Also, you have to remember, it takes something like 2.3 megajoules of energy to evaporate 1 kg of water (i.e. 1 litre of water at 4 C). That's a lot of energy (i.e. 1 megajoule is approximately equal to a 1 ton car travelling at 100 mph) so it takes a lot of energy just to evaporate water. Then you have to take into account that the water is constantly mixing and temperatures aren't entirely consistent (i.e. in a lake temperature is a gradient, decreasing in depth) in a river, it's totally messed up with flow. So in order for rivers to dry up here, we'd need to have a decade of Australian desert weather, and even then the river would still technically flow as a sub-surface river (not quite an aquifer but not a river in the conventional sense).

So to answer your question;
Groundwater flow, is a major input of river flow and probably the primary source of water in a river.
It requires a lot of energy to evaporate water, and this is even more difficult in a river.
Rivers don't totally dry up, they just move.

And in case you're wondering,
yes I love rivers and my surname is Flood!;)

Hope that made some sense!:pac:

freighter

Thanks for the reply folks. Delta bravo is after ruining my thread:D:D. I just opened up this page and it started pissing:D.

That answers my questions i do a lot of work travelling up mountains to windfarms and still see a lot of these rivers flowing away. Looking forward to that decade of australian weather:)