Building a Lake level sensor that reports back by radio to a receiver a long ways away. I have no problem figuring that out.
What I am stumped on is how to display that. I will have a measurement in inches from the range sensor that will be positioned above the lake.
I would like to make a number that is relevant to the lake and logical if possible. If I just go with the raw numbers from the sensor the starting point will be arbitrarily set where ever I happen to mount it, which seems overly random compared to putting some logic to this.
Also bigger numbers will be an emptier lake which is counter intuitive. So I need to invert the numbers(I want bigger numbers to mean more water in the lake). To do that I need to decide where zero is and calculate using the range what the current level is.
Any thoughts on what a logical place is to call zero when measuring lake levels?
The United States Geological Service(USGS) does things by measuring how high the current lake level is compared to Sea level. They then get the elevation for anything else relevant and have that handy(spillway, bottom of the lake ect)
Aside from elevation any thoughts on a logical place to put the zero mark?
The lake could be as much as 20 feet deep below the spillway. The exact number has not been measured and would depend on where it is measured. Lowest it has been seen in years is down ~10 feet. The spillway is known to flow as much as 16in deep.
With all of that in mind where is it logical to call zero?
Or am I going about this all wrong and is there is an easier way to approach this?
What is the range of the surface level of the lake?
If you don't need to match your zero to the USGS zero then I suggest you just pick any number that is below the lowest level the lake is likely to reach. Alternative pick a level that is roughly half way between the lowest and highest.
I suspect the USGS value will be an approximate average.
Indeed, just pick a zero level that makes sense to you. Could be the normal minimum, the normal maximum, a national datum... really, anything as long as it makes sense to you.
Based on that, calculate the level of the sensor, and then the lake level (the number you want to display) is sensor level minus the measured distance.
that is the bottom of your lake. of course you could just measure from the water line to the bottom with a string or some such, that is not as exciting.
You have the current lake level.
if you read 36.3 from your sensor to the current lake level, you can arbitrarily pick that level as the new zero.
if you want to show lake depth, then add that distance to the bottom.
if you have an overflow you could measure to the bottom of the overflow, what number you pick can be based on anything .
as for the measurement counting in reverse. that is simple math.
once you pick whatever you want as your zero, then, do the math
if you read 36.3 from your sensor as zero.
measured_distance = take reading
lake_level = 36.3 - measured_distance
if the lake rises to 35.1 (value goes negative)
36.3 -35.1 = 1.2 positive
the lake rose by 1.2, the distance reduced by 1.2
there is a lake by me that has an overflow dam.
if I measure from the top of the concrete of the spillway,
to the top of the water flowing over, I would get a value that I could label as water level over spillway.
if the number is 0, then no water would go over the spillway.
I could measure to the top of the emergency spillway
and say the lake level is 12 inches below the emergency spillway.
I am sure I could figure out that if the water over the spillway was 1 inch, and the width was 12 feet, that there are x gallons per minute, so you should be able to figure some neat things about the water flowing in and out of the lake.
Echoing everyone else - it doesn't matter. Just record the raw data and massage it for display. I'd guess that seeing change over time is more interesting than a single data point so just ensure that more water means a bigger number so that graphs make sense.
Pick a landmark that is not going to move. I would pick the spillway. Then if USGS wants to use your data, you can convert it to their system easily.
For a natural lake, pick a road nearby? If the road crosses the river then pick the highest point on the crown of the bridge OR the lowest point on the crossing. If you see a river height gauge on the side of the road in Australia, it is calibrated to the road's lowest point so you know how deep it is you are about to drive through.
Thanks for all the feedback. It is sounding like there is no "right" way, just whatever makes sense to me. That is a scary thought, I get to decide the "right for me" way
For now thinking I will go with the idea of picking a zero that puts the spillway at a good place. I will double check the depth of the lake where I put the meter. If it is less than 20 feet deep I will put zero 20 feet below the spillway. Then if it reads more than 20 feet(after the math sets the zero), we will know it is going over the spillway and by how much.
@the question about range. In last decade less than 12 foot fluctuation from spring flood to summer time low, before that no idea, other than the fact the lake is around 20 feet deep.
If you were asking range as in how far from sensor to water. I am not sure yet as I have not figured out how/where I am going to mount the sensor yet. 1st choice is to drive some steel railroad-track or something similar into the lake to get the sensor out there far enough yet mounted to something that is not going to move with the winter ice sheets. Once the place to mount to is solid I would probably mount this 3 feet above the level of spillway pointing straight down. The sensor needs about a foot min to work, then give me two feet extra for overflow.
If the above proves to be too much of a challenge I might try mounting it on shore at a 45 degree angle down. I can figure out the math, what I do not know if is the echo range sensor will be very good with that kind of a set up(I am guessing there will be problems with that, but that is what testing is good for).
Thanks again for the feedback, that gives me ideas on how to set up the displays the rest is fiddly-bits
MorganS:
Pick a landmark that is not going to move. I would pick the spillway. Then if USGS wants to use your data, you can convert it to their system easily.
Agreed, I need my data calibrated to something that is not going to move. That will make it so I can use it from year to year
MorganS:
If you see a river height gauge on the side of the road in Australia, it is calibrated to the road's lowest point so you know how deep it is you are about to drive through.
That is good to know and I will keep that in mind. I may be setting up other gauges where I could copy that approach.
GPS, Garmin, you know. Our local hydro power company uses percent of "full pond", full pond being the level that flood gates have to be cracked, for example "Lake Smith level is 96.7 feet". Where full pond is 100 feet. Others use feet above mean sea level, "Lake Jones level is 435.2 feet".
lake Oroville in california has been in the news over the last 2 years.
there are two web sites that I watch
OROVILLE data
this shows the monthly trend.(sometimes daily)
the headings link to graphs. and there are more links on the bottom
the one I like is the change DES CHG
it shows how much it changed from the day before. it is unsigned, so if the lever rises or falls, it does not go plus or minus, just the amount of change.
the other is lakes online
this is a summary graph of the last 2 years overlaid with the current year.
[ note, turn on the prior years by clicking boxes at the bottom]
the end of rains are around the corner and it looks like they are going to keep the lake at the top.
historically, it will loose about 150-200 feet over the summer.
As a note, you should be able to find topographical maps of your area and find some reference to the mean height above sea level. And with the IPCC doing so much climate research, they advise that if the climate changes, the worst scenario is 1 meter in the next hundred years with 1 inch in the next 50 a greater probability. so, there would not be much concern if you used any topographical maps as a reference.
The lake and river level sensors I have seen are often on structures.
such as a dam/bridge/overflow.
Since the water level is equal at all ends of the lake, there is no benefit to put it in the center.
however, if you do get a section of railroad track and drive it into the lake bottom, please set up some sort of webcam and post to youtube ! I once had the opportunity to get a section of rail when they upgraded and dang! that was some feat moving it !
As a point of curiosity, how are you actually physically measuring the water level? I have a case where I am measuring the water level in a large tank using an ultrasonic sensor. I found that I needed to put the sensor at the top of a 100mm tube submerged down into the water to get stable readings. Otherwise the splashing of the filler made waves under the sensor and readings were quite unreliable. I would think with a lake surface, waves would affect direct readings quite substantially.
gardner:
As a point of curiosity, how are you actually physically measuring the water level? I have a case where I am measuring the water level in a large tank using an ultrasonic sensor. I found that I needed to put the sensor at the top of a 100mm tube submerged down into the water to get stable readings. Otherwise the splashing of the filler made waves under the sensor and readings were quite unreliable. I would think with a lake surface, waves would affect direct readings quite substantially.
Hi,
You could use the spillway as the reference.
So;
You have measurements above the spillway, which means the spillway is flowing.
You have measurements bellow the spillway, which means the spillway is not flowing.
As you do not have a level lake bottom, having a reference that everyone can see or imagine may be the way to go.
I can remember, as a kid, the country radio water reports for some of the local weirs, reporting above or below the weir measurements.
Railroad track not being strong enough? I am hard pressed to think of anything stronger. I think the stuff we have around here weighs around 120 pounds to the yard. Driving it into the lake bottom would be a challenge without a steam driver. I can see some ways to do it with either a tractor or a CAT, but neither are currently near the lake in question
The mounting is going to be a bugger as there is currently no structure in the lake and the overflow is off to one side where it is actually fairly shallow.
@gardner I have not set this station up yet, so I am interested in ideas on how to measure the distance. In another project I used water sensors(is it wet) at different levels. That is not practical in this case as I would like finer detail. I have been playing with ultrasonic sensors on smaller lakes and with enough averaging they do ok. In this project where the water will be further away most of the time I am not sure how well it will work.
Is 10cm pipe is big enough? How far away is the water you are measuring in the pipe? I would have thought the echo from the pipe after a distance would have caused a problem and that a bigger pipe may have helped(Have not tested any of that, just me thinking)
"Since the water level is equal at all ends of the lake, there is no benefit to put it in the center."
I am perfectly happy with a single reading on a lake, but thought you may like to know that the lake level on a big lake can fluctuate quite a bit from one side to the other. The biggest lake in Oregon is just a few miles away and it has three federal water gauges on it and they never agree on the height of the lake and which one is highest changes once in a while.(can be off compared to each other by several inches). These gauges are very important to local irrigators so the topic comes up often and the feds claim it is not their gear and that is what is actually happening with the water.
The problem with anything driven into the bottom is that ice will freeze around the object and is the water rises will tend to pull the post out of the bottom
RE: water level from one side if the lake to the other - common actually - due to wind - the wind can pull the water from one side of the lake and pile it up against the down wind side. Think what happens when you blow across a bowl of soup.
What about anchoring a floating device in the lake with reflector on it and using a laser-level from the shore to figure out the vertical angle to the reflector and work out the height of the reflector by simple trigonometry.
You obviously have no idea of the power of ice. When the ice of a lake starts moving, your railroad track will bend over easily, or just be pulled out of the ground. Ice can take out trees, it can destroy whole homes.
Easiest is if you have a dam, or a quay, or other near-vertical piece of shoreline where you can mount your sensor to, above the water. For a largish lake do this on several points along the lake and you'll see the effect of wind on the water level. For really large lakes, you may even detect tides.
So, no pre-existing structure in the lake and even though you have the budget to build one, it's unlikely to have water at the foot of the structure when the lake is low. Is that a good summary?
One solution is to measure the pressure at the "bottom" of the lake. That can easily tell you the height of water above that point. It doesn't have to be the true bottom, just a point that won't be dry in the worst drought. Regular pressure sensors don't flow any water, so any speck of mud that drifts into the pressure port will just sit there and won't move out. That will eventually block your sensor and you obviously don't want to pull it out and clean it every few months.
The best solution I've seen for that is a "bubbler". An air pump on the shore pumps air down a tube to the "bottom" measuring point. Once the tube is filled with air and bubbles are coming out the other end, then the air pressure in the tube is equal to the pressure at the bottom. So the pressure sensor isn't at the bottom of the lake - it's up on the shore where you can service it if required. There's no wires going under water. You only have to run the pump for a minute to get a reading, so it doesn't need a lot of power to take 2 readings per day.
