Flumes – installing for decades of flow measurement, Part 1

What is a flume?  Most people think of long flumes that carry water across a canyon, or along the edge of a mountAlong_Aqueductain, to get water through steep country.  These flumes are expensive and time-consuming to build so they have to make economic sense.  In early
California, flumes were used to get water from a stream to gold-bearing gravels Pipe_Flume_From_Endwhere there wasn’t water.  Gold was certainly worth the expense!  It takes water to wash gravel over a washboard so gold can settle out in the ribs or slats.  Flumes were then used to transport cut logs from the mountains down to mills in the valleys.  Lumber also brought in enough revenue to make flumes worth it.

 

The kind of flume for measuring flows is a concrete, metal, fiberglass, or wood structure built to exact dimensions.  The newly-built flume shown below is formed concrete.  It took 4 days for a crew of 5 people to make this.  This flume is 3.0′ wide, and will be used toFlume_newly_installed_edited measure diversions of up to about 16 cfs.  This device could last for 40 years before it becomes too worn to be accurate, or develops cracks that let parts of it settle.

Parshall_Flume_DimensionsFlumes are much more expensive than a weir box with boards.  It costs 3 or 4 times as much to install.  On the plus side, there are no boards to change, it measures a wide range of flows with good accuracy (+/- 5% in the first 10-15 years of its life), and it will pass debris and gravel through without clogging.

The photo below is of a flume that has been installed for 30 years.  It shows what can become a common problem: the ditch below has not been kept as deep as it should be, so the flume is “flooded out”.  The flow computed by using the staff gage depth is about 40% more than actually goes through the flume…so the ranchers who use theOld_Parshall_2 water could be shorting themselves.

Rehabilitating a flume is not impossible, but it is not often done.  The whole floor could be raised by pouring a higher concrete floor, making sure it slopes exactly the way the old floor sloped.  Usually a new measurement device is installed nearby, and the old flume is not used anymore.

More on the details and how-to’s of flumes later.  For now, we sure appreciate the snow and rain!

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Worried about SB 88? That’s what this blog is for! Get a device in, send a photo to the Board, record and report your diversions

Worried about SB 88?  That’s what this blog is for!  Read here to select a flow measurement device, install it, send a photo to the Board, record your flows, and report them as required.  You will find most or all of the information you need in here.  If you need help, Rights To Water Engineering can help you meet the law quickly and at a relatively low cost.  (530) 526-0134

California Senate Bill 88 is effective as of January 1, 2016, 11 days ago as of this posting.  Here is the part that affects private or small agricultural diverters the most:

SB88_Art3_Clip

Is John Stealing Water?? Orifices – Right Size and How to Measure

Is John Stealing Water??  John Casey has a cattle ranch near Adin, where he grows pasture and hay to raise about 70 Angus steers.  His place is 240 acres with lower irrigated land and forest on the higher part.  He has an adjudicated water right of 2.00 cubic feet per second (cfs) from Preacher Creek, to irrigate 80 acres.

John’s downstream neighbors claim he steals water.  He says he can show that he takes only 2 cfs, or less when the flow drops down in the summer.  Can he prove it?John_Headgate_edit

As we can see, he has a square headgate at the head of his ditch.  It is 2.0′ wide, and can open up to 1.5′ high.  Right now, John says he is diverting 1.05 cfs.  His evidence is that his gate is open 0.15′, the water is 0.57′ deep on the upstream side, and the water is 0.20′ deep on the downstream side.  Is that enough to check what he says?

The box in which the gate sits has smooth walls, and the gate closes flush with the bottom when John is not diverting.  The water continues in a straight path from upstream to downstream.  That means the weir has “suppressed” sides.

This is in contrast with, for example, a hole cut in the middle of a 2″ x 12″ weir board.  The water on the sides has to make the turn to go straight through, so the hole in the board is an example of a “contracted” orifice.

Let’s look at the tables for orifices in the back of the Water Measurement Manual.  Table A9-3 is for submerged, suppressed weirs.WMM_Table_A9-3_suppressed

We can’t see the downstream side of the weir, but the water is above the bottom of the edge of the gate, so it is submerged rather than free-flowing.

This table has flows calculated for a minimum area of 2.0 square feet (sq. ft.).  However, the area of the opening at John’s headgate is 2.0′ wide x 0.15′ high, or 0.30 sq. ft.  Fortunately, the equation, Q=0.70A(2g Δh)^0.5, is listed right at the top of the table.  We can calculate the flow using that.  Q is the flow in cfs, A is the area of the orifice hole, g = the acceleration due to gravity, or 32.2 ft/second^2 (feet per second squared), and Δh is the difference between the upstream and downstream water depth.

So the flow Q = 0.70 x (2.0′ x 0.30′) x (2 x 32.2 x 0.37′)^0.5 = 1.03 cfs.  So far so good – John is taking 52%, or just over half of his right when 100 percent of flows are available.  But, how much flow is actually available right now?

Let’s use the “sum of the boxes” method.  Instead of measuring the amount of water in Preacher Creek at the top, before any diversions, and then estimating how much flow is being lost to evaporation, transpiration, and infiltration, and then estimating how much flow is subsurface above John Casey’s ranch and “pops up” out of the ground below, we’ll look at what each diversion amount is, plus the amount still in the creek after the last diversion.  This is very useful because none of the instream losses have to be estimated – we just add the diversions and flow still in the creek, and that amount IS the available supply.  Some Superior Court judges in past decades were pretty smart and actually ordered that available flows be calculated this way.

Susan_1_of_2_DecreeParaAvailWaterEqualsDiversionsSusan_2_of_2_DecreeParaAvailWaterEqualsDiversionsThe paragraph above, from the Susan River Decree, defines available water supply as what is being diverted, plus the flow passing the last diversion.

There are 4 diversions on Preacher Creek, and here are the amounts being diverted:

  • Diversion 1 (John Casey) 1.03 cfs  of a 1.60 cfs water right, 52% of his total right
  • Diversion 2 (Amy Hoss) 1.67 cfs  of a 3.80 cfs water right, 44% of her total right
  • Diversion 3 (Mark and Cindy Sample) 0.55 cfs  of a 0.88 cfs water right, 62% of their total right
  • Diversion 4 (Quint and Marcie Minks) 1.32 cfs  of a 2.50 cfs water right, 53% of his total right
  • Flow still in the creek past the Minks Diverison – Quint estimates about 0.7 cfs

The total diversion-plus-bypass flow is about 5.3 cfs.  The total rights on the creek are 9.48 cfs.  Therefore, the total available flow = 5.3 / 9.48 = 56%.

So, John is right, he is not stealing water!  He is taking 52% of his water right, when he could be taking 56% according to the “sum of the boxes” method.  Not only that, but Amy could take more, the Samples should reduce their diversion, and the Minks’s could take a tad more.  Well, that’s theoretical – Quint and Marcie Minks probably cannot seal up their dam completely, so there may be a little bit less flow actually available for diversion.

Some Hope in Rain and Snow Totals

Here is some hopeful news for California water supply – rain and snow totals for the year are at or a little above average, for the Central Valley Basin – The Sacramento-San Joaquin bowl that happens to contain one of the world’s greatest breadbaskets and salad bowls.  This information is measured and reported by the California Department of Water Resources.

Northern Sierra Precipitation so far this year:

nsp8s1_20151227

 

Southern Sierra Precipitation so far this year:

ssp8s1_20151227

 

California Snow Water Content, so far this year:

CSWC_20151227

 

 

Chilean Water Rights at (darn near) the Driest Place on Earth

California seems like a big place to me – I live here.  However, to cover the land surface of earth would take 400 Californias.  There are other places of interest on this celestial ball, like Chile.  What’s amazing about Chile?  The following information comes from various sources and I have not fact-checked it all:

  • 1/3 of all the copper in the world is mined here.
  • Easter Island and its amazing, huge head statues are part of the country.
  • It is a very secure country for residents and tourists.
  • It’s in the Southern Hemisphere (I hope that wasn’t a surprise!)
  • The world’s smallest deer, the pudú, is from there.
  • The people are extraordinarily friendly to visitors.
  • It has the driest “non-polar” desert in the world.  Drier than Death Valley in California??  Yup, it is:  The Atacama Desert in Chile gets 1/25 (0.04″) of an inch of rain per YEAR on average.

It is that last fact, about the Atacama Desert, that makes an amazing story about water rights.  Amazing to me, and hopefully to you, too.

Map of Chilemap_of_chile[1]

In March of 2015, there were very unusual, heavy rains in the desert, and sadly, over 100 people were killed.  Several cities were hit with floods, including the place of interest for this post, the City of Copiapó.

Atacama Desert, by Evelyn Pfeifferimage

The ongoing, increasing problem is not floods, but lack of water.  Of course generations of Chileans have learned to live with that so they have water year-round.  However, recent increases in copper mining have required proportional increases in the use of water as part of the mining process.  (My mining expert friend Mark can correct me here if needed).

Ironically, in 1981, Augusto Pinochet, the formidable dictator, changed the water code so the government has much LESS control, so water rights are much more free market.  Not only can mining companies pay much more, up to $750,000 per acre-foot according to Copiapó city officials, but they can use water than runs on their own properties for free.  [An acre-foot is 43,560 cubic feet of water, or 325,851 gallons – 326,000 gallons near enough, and the amount used by 1 or 2 families per year.]  Given that mining companies have bought a significant chunk of farm land with water rights, that gives the companies the lion’s share.  The increased pumping and new city wells are pulling in more brackish or salty water, at the same time that there is much less water available.

City of Copiapó, ChileCopiapó_atardecer_de_Otoño (1)

In California, city residents might pay up to $4,000 per acre-foot of water, roughly speaking.  I know I’ll get corrected by more than a few people on that.  The highest-profit agriculture might pay up to $1,500 per acre-foot of water.  San Diego’s desalination plant that is being built right now, is expected to cost residents maybe $1,200 per acre-foot of use.

Thankfully, our State’s founders wrote us a good Constitution; it specifies that all water must be used reasonably and beneficially.  Human health and safety are the highest priorities.  Somehow, some way, water gets to 99.99% of people even in a severe drought.  In addition, California is one of the great breadbaskets of the world, even in a severe drought.  Folks, we are blessed in the State of California!  Go see some of the rest of the world, and it will increase your appreciation of our abundance of water, and even thankfulness for our confusing, multi-basis, and to some people “oudated”, water rights system in California.

Dunes of the Atacama, by Evelyn Pfeiffer

The photo above could be of the Anzo-Borrego desert in southeastern California, but it’s from the whole lot drier Atacama Desert in Chile.

From weir to orifice in only an hour

Orifice devices are needed for flat ditches, where the fall may be as little as 0.20′ (2.4″) from upstream to downstream.  An orifice is simply a hole through which water flows, so it can be accurately measured.  The photo below shows a submerged weir, flowing from right to left.  The water in the ditch downstream (left) is above the hole in the boards.Orifice_Side_Top_2 You already noticed the amazing thing about this orifice, didn’t you?  I could tell you are savvy that way.  Yes, this is the same Briggs Manufacturing weir box as the ones in the previous post!  It has the same 2″ lumber in the upstream board slot.  Now the flow goes through a precisely cut hole in the boards, with a known area, instead of over the top of the boards.

Staff_GageInstallation is just like with the weir boxes installed in the previous post, too.  For convenience, staff gages may be attached to one side of the box so it is quick to read the water depths.  So the precast concrete box is versatile, it can be used as both a weir and an orifice.  Actually, some ditches need both a weir and an orifice.  This is especially true in a ditch where a gate or boards may be put in the ditch below the weir box, to flood hay or pasture just below the measurement device.  All it takes is a change of a couple of boards.

WMM_Cover_small

 

 

 

 

 

The big difference in measuring the flow is that, instead of “sticking” the weir boards, now the depth of the water must be measured upstream and downstream to use a weir equation or table.  The “difference in head”, or water surface elevation, gives us a value needed to read the table or use an equation to figure out the flow.  What tables or equations?  These are out of the water measurement bible, the Water Measurement Manual.  We will discuss these very soon in following posts.

This was a quick post to show how you can get 2 uses out of one device, to make your life simpler.  That’s all for now, hope you had a Merry Christmas!

 

Weirs – Planning, Building, And Measuring Flows

Tomorrow is Christmas 2015!  Merry Christmas all.

Weirs are the least expensive permanent measurement device you can install.  Materials will cost the diverter in the range of $300 to $2,000; hiring the backhoe to set it in place probably costs more than the materials, unless the diverter already has a backhoe or crane.

The weir below was precast by Briggs Manufacturing in Willows.  The weir is a cast concrete, 3-sided box with board slots for 2″ lumber.  It’s pretty simple, and relatively easy to install.  This particular weirWeir_Showing_Board_Slotsneeded metal wing-walls to keep the dirt on the sides from washing out.  Note that there are two board slots on each side, one for the boards to slide in, and the other to help make sure a nappe or air gap is created as water flows over the boards.

Step one is determining if there is enough fall in head from upstream to downstream.  A weir needs 0.7 feet (0.7′), or 8.4 inches (8.4″) of fall to be sure it will work correctly.  The 0.7′ figure is because the pool of water needs to be a maximum of 0.45′ above the top of the weir boards on the  upstream side.  Then, the water in the ditch downstream of the weir needs to be at least 0.25′ below the top of the boards so the water flows freely, separating from the boards and having an air gap on the downstream side.  0.45′ + 0.25′ = 0.70′.Sticking_Weir_sharpened

The photo above shows a ruler in tenths of a foot, held vertically on top of the weir boards.  This is called “sticking the weir”.  When the ruler is turned face-on to the flow, the water will climb up to the same level as the flat pool upstream of the boards.  It’s physics – standing water has an energy level equal to the height of the water surface.  Moving water has both potential and kinetic energy, so the energy level or line is above the surface of the

Sticking_Weir_zoom_sharpenedwater.  Moving water stalls behind the face of the ruler, giving the height of the water if it were standing still.  That is the water depth that has to be measured for weirs.  The photo is showing a water level of 0.31′ – it wobbles up and down just a little – so we know this weir is flowing at about 0.6 cfs per foot of width.

If the ditch is very flat and shows no ripples when flowing, it’s probably too flat, and an orifice or a flume will be needed instead of a weir.  Future posts will discuss those measurement devices, and others too.

Step 2 is figuring out how big a box is needed.  Fortunately, there is an easy rule.  1.0′ feet of width is needed for every cubic foot per second (cfs) that will be diverted.  For example, if the diversion will be a maximum of 3 cfs, then the diverter will need a 3′ wide weir.contracted_weir  If in doubt, get the next larger size since the cost is not much more.  The reason for this rule is that a weir can be accurate to plus or minus 5%, well within the accuracy needed for diversions in the field.  If the pool upstream of the weir boards is more than 0.45′ over the top of the boards (or less than about 0.1′ over the top of the boards), the accuracy of the weir is worse than the standard.

Measurement devices need to be planned and operated correctly to assure the diverter (and ditch-tender, and neighbors, and the State Water Resources Control Board, andsuppressed_weirpossibly 10 other state and federal agencies, and possibly even the Superior Court in the very worst case) that the flow measurement is correct.  It’s like a truck speedometer – they can get less accurate over time.  It’s no problem if they read faster than the driver is actually driving, but if they read slower, the driver is in danger of unknowingly speeding and getting a ticket.  Ouch.

The actual installation process is fairly simple to describe.  Get 1 to 4 yards of 3/4″ minus road base rock delivered on site, trucked from the gravel plant.  To save a lot of hassle, skip the forming up and pouring a concrete weir, and just call Briggs Manufacturing and order a weir to be delivered on site.  Dig a shallow, level (flat), square hole in the bottom of the ditch, about 8″ deep, and 1′ longer and wider than the bottom of the weir.  Shovel base rock into the hole about 2″ deep, and compact it.  Rent a gas-powered thumper, or use the bucket of the backhoe.  Pour another 2″ and compact it.  Use a level and make sure the top of the base rock is level side to side, and along the ditch.  Since it packed down during compacting, add the last 1″ and compact it, so the top of the road base is about 4″ below the bottom of the ditch upstream and downstream.

The installer needs to make sure to have a piece of 1″ steel bar that is about 1′ longer than the the width of the weir box.  There is one hole through the top of each side of the weir – stick the rod through that and hook onto it with a chain to lift the weir.  Set it in place, and make sure it is sitting level.  The installer might have to gently press down on one side with the backhoe to get it completely level.  Now the floor of the weir will be at the level of the bottom of the ditch.  Remove the steel bar, and fill the weir box inside about 2′ deep with some dirt.

Next, install the wing-walls, if needed.  These will keep the material on the outsides of the weir from washing out in a steeper ditch.  Then backfill with the remaining road base on the sides, compacting it for each 6″ of depth.  If tNew_Weirhe native soil holds water well, it could be used instead of base rock to backfill, saving a little bit of money.  Remember the dirt that was placed 2′ deep inside the weir?  This will keep the weir weighted down so it does not move during backfilling.  Also, it will keep the sides from being slightly bent in by the pressure of compacting the backfill.  The reinforced concrete weir boxes are strong but the walls can be bent in with enough force.

That’s it!  The weir box is installed and ready to go.  New weir boards, usually 2″ x 6″ or 2″ x 8″, should be cut about 1″ shorter than the width inside the board slots.  For example, a 3′-wide weir will have board slots about 2″ deep.  The full width from inside of board slot, to inside of the opposite board slot, is 3′-4″.  The boards should be cut about 3′-3″ long.  That way, when they swell a little bit, they won’t get impossibly stuck.

Happy measuring!  Good night to all, Merry Christmas, and blessings in the New Year.