Rising Water, Flood Stage, Dams, Sluice Gates and Flood Control

Posted by PITHOCRATES - February 27th, 2013

Technology 101

We have spent much of our History trying to Tame the Awesome Power of Water

Water can be scary.  And very powerful.  Which helps with it being scary.  We saw what happened when that storm surge hit the East Coast.  It just swept everything in its path.  For water has mass.  Making it heavy.  Just try holding a couple of buckets of water with your arms outstretched.  You won’t be able to hold them up long.  Now think about the weight of a few billion buckets.  An amount no one could move.  But there are few things this amount of water can’t move.  Except maybe a levee.  A floodwall.  Or a dam.

Also making water scary is that you don’t know what is lurking beneath the surface.  During periods of heavy rains storm sewers quickly fill to capacity.  Water backs out onto streets.  Flooding intersections.  And basements.  Streams and rivers rise above their flood stage.  And overflow their banks.  Water saturating the soil may wash it away from underneath.  Creating large sink holes.  That from the surface may look like a puddle of water.  Water overflowing riverbanks can hide many dangers.  Submerged debris that can entangle you.  That have swift and dangerous currents flowing through them.

Rising water can get into areas where it doesn’t belong.  It got into the subway tunnels in New York.  Causing a lot of damage.  It got into the basement electrical rooms at the Fukushima Daiichi nuclear power plant in Japan.  Causing a lot of damage.  Including a partial meltdown of the reactor core.  A failed levee can flood a city.  Like New Orleans.  So untamed water can do a lot of damage.  And we have spent much of our history trying to tame the awesome power of water.

Each Spring the Snows melt and the Rains come Swelling Rivers beyond their Flood Stage

Early cities rose on rivers.  For rivers were our first highways.  The river’s current turned water wheels to power our mills and factories.  Provided irrigation for our farms.  Etc.  Rivers allowed cities to come to life.  Which is why a lot of our cities today have rivers flowing through them.  Yes, a river view is beautiful.  And the recreational opportunities are plentiful.  But they are not why we founded these cities on rivers.  It was all the benefits the river provided.  Things that allowed a civilization to grow.  But it wasn’t all good.

Each spring the snows melted.  And the rains came.  Swelling rivers beyond their flood stage.  Overflowing their banks.  Bringing great damage to life along the rivers.  Especially to the towns on its banks.  So we did something with these rivers that were prone to such damaging flooding.  And built a dam upstream.  To control that flooding.

They would choose an appropriate location upstream.  Some place where the river valley narrowed a bit.  So they could build a dam across the valley.  Once they did the water upstream of the dam rose into a lake or reservoir.  Providing a source of drinking water.  Irrigation water.  Recreation.  Or power generation with a hydroelectric dam.  Very beneficial things.  But all secondary to its main purpose.  To eliminate that recurring flooding.

A Dam’s Sluice Gates are the Key to Flood Control

If you’ve ever seen a dam on a river you probably noticed some things.  Turbulent water at the base of the dam on the downstream side.  Warning signs and some sort of a barricade (such as a chain stretched across the river held up with floats) a hundred feet or so in front of the dam on the upstream side.  Signs you would be wise to heed.  For great danger lurks beneath the surface of the water.  In that dam are underwater openings.  That have moving gates to make these openings bigger or smaller.  Sluice gates.  And you don’t want to be anywhere near these gates whenever they’re open.  For the weight of a few billion gallons of water creates a powerful force of water moving towards those gates and through the openings.  If you ever thought of diving off a small dam don’t.  You would be sucked quickly to these openings.  If they are not opened enough for your body to fit through the force of the water would hold you against the openings until you drowned.  If the opening is large enough the water will flush you through with great force and violence.  Discharging you into the turbulent water on the downstream side of the dam.

These gates are the key to flood control.  During the snowmelt runoff and heavy rains of spring we can close these gates to allow only a trickle of water flow.  Maintaining a safe river level downstream.  The excess snowmelt runoff and the rains will fill the lake or the reservoir upstream of the dam.  After the rains stop they can open the gates a little more to bring down the level of the lake or reservoir.  Without sending the river downstream above its flood stage.  If the level rises too high behind the dam the water will enter a spillway and flow over/around/through the dam.  Like an overflow in a sink.  Allowing the water to rise only to a maximum level behind the dam before spilling over/around/through the dam.  Joining that turbulent water on the downstream side.  Which you want to avoid as much as the dangers on the upstream side of the dam.

We haven’t always been successful in controlling the awesome power of water.  Some dams we’ve built have failed.  Like the Teton Dam in Idaho.  An earthen dam.  Just upstream of Wilford.  Built for flood control.  To protect the towns and farmlands downstream of the dam.  As it turned out, though, the Bureau of Reclamation did a poor job building the dam.  And the rains were heavy that year.  Raising the level behind the dam 3 feet a day instead of the designed 1 foot.  Water started leaking through the dam.  Saturating the soil making up the dam.  The water rose rapidly.  But before it could reach the spillway the dam gave way.  Sending some 80 billion gallons of water rushing downstream.  Wiping out Wilford.  And destroying most of Sugar City.  And Rexburg.  Causing damage as far away as 30 miles downstream in Idaho Falls.  Illustrating the awesome power of water.  And the price we pay when we don’t give it the proper respect.



Tags: , , , , , , , , , , , , , , , , , , , ,

Outhouse, City Water, Sanitary Sewer System, Flush Toilet, Water Trap, Soil Stack, Sanitary Lift Stations, Weir Dam and Overflow Spillways

Posted by PITHOCRATES - April 11th, 2012

Technology 101

Before Indoor Plumbing People had to Walk some 50 Feet in Rain, Snow or Shine to go to the Bathroom

On the American sitcom The Beverly Hillbillies, Jed Clampett wasn’t sure if he should move his family to Beverly Hills after they found oil on his land.  He asks his cousin Pearl for advice.  She says, “Jed, how can you even ask? Look around you. You live eight miles from your nearest neighbor. You’re overrun with skunks, possums, coyotes, and bobcats. You use kerosene lamps for light.  You cook on a wood stove, summer and winter. You’re drinkin’ homemade moonshine, and washin’ with homemade lye soap. And your bathroom is fifty feet from the house. And you ask should you move!?”  Jed thinks about all of this and replies, “Yeah, I reckon you’re right. Man’d be a dang fool to leave all this.”  (This exchange begins at 11:40 on The Beverly Hillbillies (Season 1 – Ep. 1) The Clampetts Str).

On the American sitcom I Love Lucy, Tennessee Ernie Ford comes to visits the Ricardos in New York City.  On the day of his arrival, as he prepares to go to bed, he walks out of the apartment through the kitchen door with his suitcase.  Lucy and Ricky look at each other perplexed.  After a few minutes he comes back in and walks out of the apartment through the living room door.  After a few minutes he returns and approaches Ricky.  And whispers in his ear.  Exasperated, Ricky points and says, “Through the bedroom.”  In stunned disbelief Ernie says, “You mean it’s in the house?”  Ricky nods.  Ernie walks towards the bathroom and says, “Wait till I tell Mama about this.”  (See I Love Lucy Tennessee Ernie Visits).

Once upon a time, before indoor plumbing, people headed out of their house some 50 feet to go to the bathroom.  In rain, snow or shine.  To an outhouse.  Away from the main house.  Because of the stink.  And to keep their waste from seeping into the water table.  So their waste didn’t contaminate their drinking water.  So when they ever felt the call of nature they took that long walk.  Pushed open the door and squatted.  (Interesting fact: all outhouse doors open in for safety.  For if you were inside when a strong wind tipped the outhouse over you could open the door and then stand up, lifting the outhouse upright).  Or if it was a deluxe outhouse you may have sat down on some wooden planks.  Living like this was all well and fine when your nearest neighbor was 8 miles away.  Or in a suburban community with deep backyards.  For you could put your outhouse at the back fence.  Like your neighbor across the fence.  You can.  And some have.  But it’ll put a stink in the air.  And provide little privacy to do those most personal of things.  For when your neighbor sees the lady of the house walking back there it’s no secret what she’s going to do.

Flush Toilets are Possible thanks to City Water, Sanitary Sewer Systems, Water Traps and Stack Vents

Moving the bathroom into the house gave us true privacy.  So a lady could have a bowel movement without her neighbors knowing about it.  Two things made this possible.  City water.  And a sanitary sewer system.  These two things gave us the flush toilet.  A true marvel of engineering.  A porcelain bowl that holds a small amount of water.  Sitting on top of a pipe that ties into the sanitary sewer system.  A thing that makes the stink of an outhouse seem like a bouquet of roses.  Yet that stink doesn’t enter our homes.  Why?  Because of a simple thing called a water trap.  They come in a couple of shapes but typically have a u-shape somewhere in them.  Water enters and leaves at higher elevations.  Leaving the lower part always filled with water.  Providing a water seal between us and the stink of the sewer.  Thus preventing gases from entering our homes.  We build this trap right into our toilets.  On some models you can actually see the curly path the bowl drains into on the side of the toilet.

On top of the toilet base is a water tank.  With a valve and a float.  City water (under a slight pressure from the water plant) enters the tank through this valve.  When the tank is empty the valve is open and the water flows into the tank.  When the tank fills the float rises and closes the valve, shutting off the water flow.  At the bottom of the tank is a flapper valve.  When the tank is full of water the weight of the water presses down on this valve, sealing it shut.  When we flush the toilet we lift this flapper valve via a chain connected to a lever we operate with the flush handle on the toilet.  When we lift the valve the water in the tank can flow into the toilet bowl, washing the contents of the bowl into the pipe the toilet sits on.  As the water empties from the tank the flapper valve falls and seals the tank.  And with no water in the tank the float falls, opening the valve so water can refill the tank.

While the toilet tank fills because of the slight pressure they keep our city water under, the sanitary sewer system works under gravity alone.  All sewer lines in a building slope downward.  When they join other pipes they join in a ‘Y’ connection to make sure the new water entering another pipe enters flowing in the same direction of the water already in the pipe.  So as not to create any agitations or backpressure to the gravitational pull on the water.  To keep this water flowing in the downward direction.  If you have a basement in your house you can see a lot of this.  Downward sloping.  Y-fittings.  And you’ll also see one or two vertical pipes.  Soil stacks.  That other horizontal pipes run into.  Your sanitary waste (from floor drains, showers, sinks and toilets) flows to these soil stacks and down to a pipe under the floor that runs out to the sanitary line under the street.  If you follow these soil stacks up you’ll notice that they run all the way through the basement ceiling.  They in fact run all the way up and out through your roof.  Those little pipes you see protruding from your roof are stack vents.  These stack vents are critical in helping gravity work in your sanitary plumbing system.  By keeping a neutral pressure inside the pipes.  Making air pressure inside the pipes equal to the air pressure inside the house.  By equaling the air pressure on either side of the water traps the water stays in these traps.  If the system wasn’t vented the water wouldn’t stay in these traps.  As the column of falling water would compress the air below it creating a high pressure.  While creating a low pressure or vacuum above it.  Which would suck the water from the traps into the system above the falling water column.  And blow out the traps below the column.  Which would be rather nasty in the bathroom.  For it would blow raw sewage out of your toilet.  And onto you should you be in the bathroom at the time.

Sanitary Lift Stations have Backup Power and Failsafe Designs like Weir Dams and Overflow Spillways

At the beginning of all sanitary sew systems the pipes are their smallest.  Like inside a house where they connect to a floor drain, shower, sink or toilet.  As they join other pipes the pipe size increases.  To accommodate the increase in water volume.  The biggest pipe in a house is the one running to the sanitary line under the street in front of the house.  Which is a much bigger pipe as a sanitary line from each house connects to this line.  So it has to be big enough to handle all of the flow if everyone flushed their toilets at the same time.  Like at halftime during the Super Bowl.  And the pipes these ‘street mains’ connect to have to be even bigger.  For multiple ‘street mains’ connect to them.  And as more pipes join together they connect to even larger pipes.  And every one of these pipes is sloped downward to maintain the flow of water.  Pulled along by gravitational forces alone.  Which causes a problem.  Because continuously sloping bigger and bigger pipes downward will drive these pipes deeper and deeper underground.  Which can’t go on indefinitely.  As the ultimate destination is a wastewater treatment plant.  Which we typically don’t build underground.

So along the way we have to raise this wastewater so it can start its downward course again at a level closer to the surface.  We call these points sanitary lift stations.   Where a big pipe enters a wet well inside the station at a low elevation.  And exits the station at a higher elevation.  As water enters the wet well the water level slowly rises.  When the level reaches a certain elevation an automatic control system turns on pumps.  But not just any kind of pumps.  Some pumps with teeth.  That can grind up any solid waste that enters the sanitary sewer system.  From human waste.  To used condoms.  To feminine hygiene products.  And the myriad of other things that we shouldn’t flush down our toilets but do.  These pumps can pretty much grind up anything and spit it out into the discharge pipe of the station at a higher elevation.  So this wastewater can continue its journey to the wastewater treatment plant.

Some cities have a combined storm water and sanitary sewer system.  Which can tax the system during heavy rains.  For the water flowing into these wet wells will keep that level rising to a point the pumps may run continuously.  And should there be some damaging winds that take down the electrical grid these lift stations will throw-over to an emergency backup generator.  To keep those pumps running when we need them most.  To keep the water from rising too high in the wet well.  And the pipes feeding it.  For if those pipes fill up completely there will be no place for new water entering the sewer system to go.  Water will rise in manholes.  And out onto our streets.  Even out of our floor drains and into our houses.  As this would be a grave public health concern they often build failsafe protection in the sewer system.  The feed to the lift station will be a Y-connection.  Just past this will be a weir dam in the pipe.  A dam that blocks only the lower portion of the sewer pipe.  The pipe past this will run to some spillway into a river, lake or ocean.  If the flow in the pipe is too great for the lift station’s capacity it will spill over the weir dam and flow untreated directly into a larger body of water.  While this is bad it doesn’t happen often.  As it typically takes a ‘once in a hundred years’ rain to overtax a system.  And when it does there is so much storm water in the system that it greatly dilutes the harmful pathogens in the wastewater.

Our Sanitary Sewage Systems allow us to Draw Clean Drinking Water in the Same Room we Poop In 

Sanitary systems are gravity systems upstream.  As they get further downstream they get an assist from pumps.  As well as other powered valve and gates to redirect the water flow as necessary.  The bigger our cities get and the denser our city populations grow these active components become ever more critical to the gravity systems upstream.  So we provide backup power systems and failsafe designs.  We do everything possible to keep that wastewater flowing downstream and out of our homes.

Some of the greatest public health crises happen when these active systems break down.  For the power of gravity may influence our world a lot.  But the power of water is something to fear.  Especially when we lose control of it.  From tsunamis that overwhelm sewage systems in our coastal areas.  To 100-year rains that overwhelm our sewage systems in our interior areas.  To lift stations that fail and reverses the flow of wastewater in our sewage systems.  Worse yet is the discharge of raw sewage into our freshwater supplies.  That contaminate our fresh drinking water.  It doesn’t happen often but when it does it’s a health crisis of the first order.

But most times these systems work so well that we never think about them.  And can’t even imagine what life was like when you had to bundle up in the middle of winter and wade through thigh-deep snow to get to your bathroom.  Sitting on wooden planks in an unheated structure with the wind blowing through the slats.  Today we’re spoiled.  Not only do we not have to bundle up our bathrooms are heated.  And only a few steps away from us.  Because they are in the house.  Thanks to our sanitary sewage systems.  That can keep up with the waste production in our largest cities.  And allow us to draw clean drinking water in the same room we poop in.  If you really think about that it’s hard not to be as amazed as cousin Ernie was in I Love Lucy.



Tags: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,