Monthly Archives: April 2012

The wrong type of rain; or, why there are floods during a hosepipe ban

This country is in a recession. Are we not all miserable enough without the recession spreading to our weather, dammit? We do not have enough water. But how can this be, people cry despairingly, when there is all this wet stuff pouring out of the sky constantly?

My favourite explanation comes from an old schoolfriend – Ashwin – who is a gentleman, a scholar, and a wit. He posits that “the first 22% of rainfall goes to Her Majesty’s Revenue and Customs, unless there is lots of rain, in which case, Her Maj takes 40%”.

The popular press (and by this I mean the Daily Mail and its ilk) will, inevitably, go for the most attention-grabbing, frothworthy headlines they can. They will scream about flood warnings while moaning about a hosepipe ban, shouting: “Why why why? Look at all this water – how can there possibly be a drought on?”

Often, they then go on to blame the Met Office for the droughts, then the floods. Which is funny in itself. Unless these pesky meteorologists really are sitting in a secret volcano lair somewhere controlling the weather. In which case, the Daily Mail has been right all along and life as we know it is coming to a soggy end.

There are floods during a drought. And there are very good reasons why. They are also interesting reasons, so it’s a real shame that most people aren’t given the facts.

In Warwickshire, it’s been raining. A lot. More on than off for the past two weeks, and almost continuously for the past three days. That’s quite a lot of rain – 50mm in some places on Wednesday alone – and it has followed two unusually dry winters.

Several factors cluster together to pose a flood risk. But first things first: where did all this rain come from in the first place?

Water, water, all around…

A particularly strong jet stream is currently separating warm, moist air in the south (an area of high pressure) from cool air in the north (low pressure), creating a front. Jet streams are fast-flowing, narrow currents of air high in the atmosphere (near the top of the troposphere – the tropopause) which blow from west to east. Their locations are not fixed; they tend to meander around, but their position helps with weather prediction.

At the moment, the warm, moist air from the Mediterranean is flowing north (air travels from areas of high pressure to areas of low pressure) into the low pressure zone over the UK. Because warm air is less dense than cool air, it is forced upwards above the cool air.

As the warm, moist air rises, it cools and its water content condenses into rain-clouds (cool air can carry less water vapour than warm air). If the front stays steady, the rain will persist as long as the clouds are being fed by a flow of warm, moist air from the south.

Unfortunately for us (but fortunately for our gardens) the front is persisting, as is the seemingly endless precipitation…

But we’re suffering from a drought, aren’t we?

But why then, you may ask, is there a hosepipe ban across much of the country? As mentioned above, the UK has experienced two unusually dry winters. These two dry winters mean that the UK is now suffering from a water shortage. Reservoirs of water have been depleted and it takes time – and a lot of rain – to refill them.

Almost everyone knows about freshwater reservoirs – man-made lakes created specifically to provide stores of drinking water. These are replenished by rain and by rivers and streams. Fewer people realise that an awful lot of our fresh drinking water is stored as groundwater, in the rocks themselves. Just one per cent of all freshwater is accessible to humans, and of that, four million cubic kilometres is located underground. In the pores and cracks in the bedrock, and between the grains of rock themselves.

Water in the ground

Rock that is porous and permeable enough to store water and allow it to flow through easily are called aquifers, and most of the UK’s aquifers are located in the southeast of England – notably the Chalk (which is a soft, white limestone with a network of fine cracks, giving it high permeability). Individual boreholes in the Chalk can yield more than 10 million litres of water each day, which can provide for around 70,000 people.

That’s a lot of water.

Groundwater is not only accessed via boreholes, it also helps to replenish rivers. If rivers were only fed by runoff from the land, they would quickly dry up after the rain stopped. Rainwater that passes through the surface of the land soaks down through the underlying soil and rock until it reaches the water table – a level when all the pore spaces in the rock are full of water. The water table separates the unsaturated zone from the saturated zone – and the saturated zone is called groundwater.

The drought persists even after prolonged heavy rain because recharging the saturated zone takes time. There’s an awful lot of ground for the water to soak through, and the water table level will recover only slowly. And the first bout of heavy rain after a prolonged dry period, such as that the UK experienced in March, won’t do much to help – parched, hard ground won’t absorb water easily, so it simply runs off the top. It will, of course, gradually soak in, but not straight away…

Which leads us to why there are flood warnings

Most river floods result from extremely heavy and/or prolonged rain. Several factors can affect the intensity of flooding – area, slope and altitude of the river catchment, soil type, geology, vegetation cover, the nature of the drainage basin network, and the shape of the river channel.

However, in this instance there are two main reasons. Firstly, the sheer amount of water being pushed into the rivers by the rain itself and the runoff from the land surface. There is only so much extra water a river can take in a relatively short space of time before it bursts its banks.

Secondly, if there is a large volume of water dumped on the ground, the unsaturated zone will become saturated – it won’t have time for the water to soak down to the saturated zone before all the upper pore spaces are filled. So there will be even more runoff than usual.

So although drought and floods are both caused by precipitation (or the lack of it), different mechanisms are at play. Drought is a long-term problem that cannot be solved by a lot of rain in a short period of time. Floods are a short-term problem that are often caused by a lot of rain in a short period of time.

There are really cool (and by that, I mean nerdy) ways to predict how severe a flood is likely to be. In fact, the whole topic is pretty interesting – aquifers are marvellous things.

It’s really not that complicated at this level (of course, there are other aspects to consider, such as the deforestation of the British Isles, the amount of concrete and tarmac laid down, and the effects of vegetation on water movements, but in a nutshell, this is how you get floods in a drought). Yes, you could dig a little deeper and find an entire aquifer full of interesting scientific details to do with groundwater supplies, but a basic understanding of what causes droughts and floods is not out of the grasp of most people, so it’s a real shame that journalists don’t have the time to research and explain this. And it’s more of a shame that the press releases from the Met Office and the BBC don’t include simple, easy-to-follow explanations (and if they do – then why don’t the papers use them?).

I keep hearing wits on the radio commenting that this is a very wet drought, isn’t it? Ha ha ha. Well yes. Yes, it is a very wet drought. Two weeks’ worth of rain will not, sadly, make up for two winters’ worth of unusually dry weather. So put your hosepipes away and start conserving your water. It’s a precious natural resource, and deserves to be treated as such.

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Puddles, puddles, everywhere…

I think the water table in our garden in Warwickshire has risen to the actual surface of our garden. There has been so much rain here – and crazy hailstorms – over the past week or so that the ground is saturated. The lawn goes *squidge* when you walk on it.

This is the first of (probably) several posts about water and how cool it is. H2O is a marvellous, and profoundly odd, substance. But more about that later. It is the stuff of life, and knowing where and how it is stored and how it moves around is pretty important.

So: it rains. (At the moment, it seems to do nothing but rain, but that’s by-the-by.) Water falls onto the Earth – but then what? Some of it falls directly into water courses and drainage channels (streams, rivers, etc.). Some of it falls onto trees and plants; some of that evaporates or reaches the ground.

Only about a third of precipitation results in runoff (also known as streamflow or discharge). Runoff is the water that flows over the land and increases flow in rivers, and is measured in cumecs (cubic metres per second).

Then it starts to get complicated, with flow diagrams, code letters and fiddly rivulets finding their way into nooks and crannies unseen by you and me.

In a nutshell, here is where the rain goes:

  • Into rivers and streams (channel precipitation) OR over the land (overland flow)
  • Infiltrates into the ground below the water table as groundwater flow OR above the water table as throughflow
  • The infiltrated water becomes subsurface runoff
  • Subsurface runoff, channel precipitation and overland flow come together in channel flow (i.e. a river or stream)
  • The mouth of the river spits out the total runoff.

It’s pretty important to keep an eye on these processes, and be aware of how topography, soil type and land use will affect water courses, because that’s what helps with flood preparation.

…lots of drops to drink

What I find interesting is what happens to the rain when it disappears beneath the surface.

You’ve got the ground surface, then soil water, then unsaturated rock, then the capillary fringe, then the water table, then saturated rock. That’s quite a lot of groundwater, and much of it is available for our purposes.

Capillary action means that water is drawn into the spaces between rock grains – and into cracks and fissures – and is held there by surface tension. The larger the surface area of the rock particles, the higher the surface tension and the more water can be potentially be stored. Hold the edge of a sugar cube in a cup of hot chocolate and see what I mean. The liquid will creep up the sugar lump.

So, the amount of groundwater stored in rocks depends on their porosity, which can be calculated by dividing the volume of void space by the total volume of rock, then multiplying by 100.

Vp/Vtot x 100

Unconsolidated rocks – not compacted or cemented – are the most porous, while consolidated rocks and dense crystalline rocks are usually less porous. But just because a rock is very porous, doesn’t mean it is necessarily permeable…

Rocks with large pores, or with pores that join together, make it easier for water to flow through them. Sandstones and gravels are permeable rocks. But clay, which has high porosity (due to lots of very small pores) holds its water virtually immobile because of the high surface tension.

Porous, permeable rocks are great natural water storage vessels. They are aquifers, and most of those in the UK are found in the south-east of England. The Chalk – the White Cliffs of Dover and the rest of this particular limestone formation – has a network of fine cracks making it very permeable to water. A single borehole in the Chalk can yield enough water to provide for around 70,000 people per day. That is a LOT of water, because we use way more than we should.

There are two types of aquifer:

  1. Unconfined: the aquifer sits on a floor of impermeable rock and soaks up rain. When it becomes saturated, marked at the top by the water table, the water flows out as a spring.
  2. Confined: the aquifer lies between two layers of impermeable rock, trapping water at a higher pressure than atmospheric pressure. Boreholes – artesian wells – drilled into the aquifer allow the water to rise until the pressure equalises.

What is the potentiometric surface?

If several boreholes were drilled into a confined aquifer, the water level in each would rise to a maximum. An imaginary line can be drawn linking these maximum water levels – and this is the potentiometric surface.

If the potentiometric surface is above the ground surface, water will flow freely from the well; if it is below the surface, then water must be pumped from the well. Essentially, it is the level at which the weight of each column of water balances the  water pressure in the aquifer.

Magic

Oases in the desert are often portrayed as magical, mystical things – how, in such an arid and inhospitable place, does water flow? Aquifers; that’s how. Porous and permeable rocks lying underground can transport water many miles from a source of precipitation to the middle of a desert.

You can see why people were mystified by oases. Now we understand how they work, the appearance of water is no less wondrous.

I don’t know about you, but the more I know, the more I want to know…

Got any jobs, mister?

No, really. Have you?

I’ve never been terribly forthcoming with blowing my own trumpet; I always felt it to be unseemly, immodest and a little bit vulgar. But frankly, if I’m not going to market myself, then who on Earth is?

Here is my situation: I am a creative, talented and enthusiastic writer and researcher who is currently on the lookout for a fabulous role with a fabulous organisation.

So, why am I looking? There is always the question of why I am currently in the market for a new job. That is perfectly valid, and I can tell you honestly: my last role, although it provided me with plenty of new skills and developed some existing ones, sadly wasn’t the right one for me. The job did not turn out to be what I thought it would be, and did not provide me with the opportunities that were indicated.

I can, however, provide you with numerous references from colleagues who will be glad to tell you what an asset I would be to your organisation. (That sounds terribly vain. In real life, I’m as modest as they come.)

I’m not going to present my entire CV in this blog post. That is available on my LinkedIn profile and is currently scattered far and wide across the internet. But I am going to tell you a little bit more about what I’m looking for.

Ideally, I’d like a role that allows me to scribble some words on paper, on the web and across the wide range of social media tools available to us. To be creative, to get a worthwhile message out to a wide audience. To have good ideas and be encouraged to implement them.

I really enjoyed my time in the busy press office of a national charity, and if I could find my way back into the not-for-profit sector that would please me greatly. It sounds trite, but getting important messages out to society – especially the more vulnerable citizens, using new and emerging media – was tremendously rewarding.

The Great Job Hunt is not limited to the charitable sector, however, and my interests are many and varied: I love science (I mean, I really love science), technology and motorcycles; running, jumping and aerial acrobatics; music and the theatre; yoga; camping; water (just generally – it’s fascinating stuff); and I am, ultimately, a bit of a tree-hugging hippy. So I’m up for almost anything.

Working for a living is obviously crucial, but money isn’t everything and job satisfaction and good career prospects are equally, if not more, important to me.

I have become aware, also, that it’s not just up to candidates to sell themselves to a company; the company has to sell itself to candidates. So I’ll be asking a lot of questions when I’m interviewed. I’m bright and interested in just about everything, so be prepared for a bit of a grilling.

Incidentally, I’m not sitting idly by and waiting for something to knock on my door: I’m getting myself out there, in the real world and the online one. My marketing experience is being put to good use for a couple of good friends who have their own businesses. I’m putting a lot of effort into my Open University degree in my free time. I’m keeping fit, practising for pole competitions and running obstacle races through knee-deep mud with friends.

So, it’s a bit of a cheek, this article, but worth doing anyway I feel. Please do get in touch with me via vicky<dot>j<dot>fraser <at> gmail<dot>com if you are recruiting, or simply fancy a chat!

UPDATE: Somewhat fabulously, I’ve been offered some freelance writing work with a rather lovely design agency. So I shall be doing that too. Today has been splendid.

In praise of creative writing and a sound business plan

I’ve a plan. Well, I’ve two plans, in fact.

Plan The First

My lovely friend Gareth draws me pictures using MS Paint. This is in return for pictures I draw him on coloured post-it notes. I leave them in various places around his desk. So he emails me electronic funs, and I love them greatly.

I’m constructing, in my head, a story. A graphic novel in blog form, if you will. It will be grand, and wonderful, and not at all full of delusions. It will buckle; it will swash; it will be happy and sad, and full of derring-do. The story will be serialised, and will be illustrated marvellously using the lovely images created by  The Lovely Gareth.

Stay tuned, folks. You won’t want to miss this.

Plan The Second

I pole dance. I love it. I mean, I REALLY love it. It’s not just for skanks and hos, you know. It’s aerial dance; vertical gymnastics; a showcase of strength and grace – and I’m helping to improve its reputation among the prudes and purse-lipped curtain-twitchers of the world.

Take a look at my progress on my YouTube channel. There are lolz as well as pride in my growing ability.

Come Autumn, I’m taking my pole dancing teacher qualifications. Then I’m going to set up a dance school of my very own. I’m extraordinarily excited by this, at a time when I desperately need things to be extraordinarily excited by. So stand by. And if anyone local to Leamington Spa is interested in learning – women and men – drop me a line. I’d love to meet you.