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El Salvador water flow question

  • 1.  El Salvador water flow question

    Posted 04-11-2016 02:53 PM
    Edited by Brian Parsons 04-11-2016 02:52 PM

    Good Afternoon:

    I received the below message from a volunteer who has a question about water flow related to a volunteer project he is working on in El Salvador.  Please be in direct contact with DonMontagna@... if you feel that you can assist.  He is working  with  International Partners - Developing self-sustaining communities.

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    International Partners - Developing self-sustaining communities
    El Salvador is a beautiful country that has been ravaged by pollution, erosion and waste. Its dense population, the civil war, and lack of employment opportunities are fueling a steady migration to the United States.
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    From: DonMontagna@... [DonMontagna@...]
    Sent: Thursday, April 07, 2016 7:06 PM
    To: ASCE Staff Member
    Cc: pbeckman@...
    Subject: El Salvador water flow question

    Dear John,

    I was delighted to find out that you might be able to help with a water flow question.  I am a volunteer with International Partners, a small non-profit that works with rural Salvadoran communities of people living in extreme poverty.  They are subsistence farmers, earning maybe $300 a year, and the women have always had to walk each day for water.

    The community of Hacienda Vieja is making a proposal to improve the water delivery for a system that we had previously built.  Our water projects are simple because they are gravity fed, but I am not sure if this one will work.  Given very scarce resources, to spend money building this if it won’t work would be a travesty.  Your help with this issue would have a substantially meaningful impact on the live of 300 desperately poor people.  I cannot fully express my gratitude for you help with this.

    Let me try describing their situation and proposal.

    1. On hill #1 there is a tank with sufficient water filling it from an ample spring a few miles away.  There is no option for increasing the water into this tank or building another tank on hill #1, but there is enough water going into the tank #1 to serve all needs.
    2. Exiting tank #1 there is a pipe.  The diameter of this pipe cannot be changed nor can there be another pipe added to exit tank #1.  (Another community that also has a pipe exiting tank #1 will not allow any change and backs that up with violence.  There are no police.)
    3. That exit pipe goes down the hill to houses that are along the valley floor where houses now get adequate water.
    4. However, on the far side of the community there are houses that do not get water because they are higher so that the gravity feed will not reach them.
    5. About 5 years ago, they (with IP help) built a second tank (#2) on a hill closer to the houses without water.  The water pipe from tank #1 that feeds all houses in the valley was extended up the second hill, which is lower than hill #1, so that tank#2 gets water.  From tank #2 water is then piped down to the houses not in the valley.  
    6. The amount of water that gets into tank#2 supplies only enough for each house to get water a few hours a week, maybe 2-3 hours 2 or 3 times a week.  Their goal is to increase the amount of water in tank #2 so that those higher houses have adequate water.
    7. Their plan is to run another pipe out of the pipe that exits tank #1.  That new pipe would go a shorter route along a ridge and directly into tank#2, which is somewhat lower than tank#1.  This would be instead of having only the pipe that goes down into the valley and up again to tank #2.

    Here are the issues that concern my uneducated mind.

    1. Generally, will the water flow into the T joint across toward tank #2, or prefer to go down the steeper pipe into the valley.
    2. At night, when the water is not used by the valley houses, causing the downward pipe to fill, would the water then will flow through the higher pipe going directly to tank #2?

    Brian Parsons M.ASCE
    Eng. Director
    Reston VA
    (703) 295-6071

  • 2.  RE: El Salvador water flow question

    Posted 04-12-2016 05:36 AM

    To All,

    I am pleased to help.

    1.       Water will flow to Tank # 2 if the inlet to Tank 2  is lower than the elevation of the proposed connection to the existing pipe from Tank # 1.                 I presume that the hydraulic grade is positive (the pipe flows full) at the proposed location of the connection to the existing pipe from Tank # 1.                                                  

    2.       Yes water will flow to Tank # 2.  You  would , however, have a more reliable (more frequent) service if a connection to the outlet pipe from Tank # 2 was made at a location  between Tank # 2 and the houses that currently do not have a reliable supply.

    3.       If I had a sketch showing piping layout ground levels and tank data there may be a more rational (economical) solution.  


     Regards     Brian Stone  P.E.  M.A.S.C.E.


  • 3.  RE: El Salvador water flow question

    Posted 04-13-2016 09:43 AM
    What one would have worried about is whether there will be ample water for all the communities but the information given has put such fear to rest. One would have loved to have more information as to the main pipe size, reticulation, controls (valves?) of the system. Ditto for tank and elevations.
    From personal experience on similar issues in local communities here in Ekiti state, Nigeria, ('Ekiti' means where hills abound) I would like to agree and recommend that the pipeline to tank #2 should be constructed, taking off from the suggested T- junction and the pipe size same as the one already in place. 
    Each of the two lines have own control valve that could be pragmatically and practically throttled in favor of the new line to tank #2. In addition, individual flowmeter on each line would serve in flow assessment. 
    The purpose is to increase the pressure and consequently, the quantity of water to the new line.
    A win-win situation is achieved where the two sector recipients will receive uninterrupted flow, day or night.
    Engr. Victor Adebayo Oke
    P.E., M.ASCE

  • 4.  RE: El Salvador water flow question

    Posted 04-12-2016 09:10 AM

    To all,

    In response to your questions;

    1. Water will flow to Tank # 2 if the inlet to Tank # 2 is lower than the elevation at the proposed  connection to the pipe from Tank #1.            There will be a flow to Tank # 2 if the hydraulic grade is above ground level (a full pipe) at the connection location.                                               2. Yes water will flow to Tank # 2. You  will, however, have a more reliable (more frequent) service if the proposed new pipe was connected to the outlet pipe from Tank # 2 at a location lower than the outlet from Tank # 2. (Connect to the outlet pipe at a  location between Tank # 2  and the existing  houses that have an irregular supply.

     I am pleased to help.                                                                                                                                                                                           There may be a more effective solution if you have a plan or sketch of the existing distribution piping, ground levels and data on tanks.

    If you are allowed to make a connection to the existing pipe from Tank # 1, it will be possible to improve  pressures without going all the way to Tank # 2.

     Regards     Brian Stone P.E.  M.A,S.C.E.

    Brian Stone P.E., M.ASCE
    Claremont WA
    61 892864267

  • 5.  RE: El Salvador water flow question

    Posted 04-12-2016 09:10 AM


    In general, if tank #1 does not empty, the pipes remain pressurized, and there is sufficient head to overcome frictional losses in the pipes then tank #2 should receive water. However, to make a more informed decision it would be necessary to know the elevations, pipe lengths, pipe diameters, and pipe types throughout the system.

    Do you have any additional information?

    Christopher Best, A.M.ASCE

  • 6.  RE: El Salvador water flow question

    Posted 04-12-2016 09:10 AM
    A second pipe would reduce friction in the path to Tank 2. The closer you can make the tee connection, The more friction you will eliminate.

    This would mean more water flowing out of Tank 1, the same way a second pipe or a larger pipe would. If Tank 1 is running dry, then the violent village might take issue. 

    Is tank Number 2 filling overnight now? If it is filling now and running dry during the day, then add an additional tank might be a better solution than a new pipe.

    Richard Hanson

    Georgia Water Tanks




    Rainwater is a resource

  • 7.  RE: El Salvador water flow question

    Posted 04-12-2016 08:33 PM

    A question regarding Tank #2. Is the water that flows into the tank prevented from flowing back towards Tank #1? (does the inflow pipe from Tank #1 discharge into Tank #2 above the water line, or are there other means to prevent water flowing backwards).

    Michael College

  • 8.  RE: El Salvador water flow question

    Posted 04-12-2016 08:33 PM

    I read the information provided on the question.  Recommend:

    Get graphing paper and plot both the tank and water elevations (min and max) of all the locations using an appropriate scale (Hill #1, Tank #1, Hill #2, Tank #2, Valley Houses (floor), Hill Houses (floor)).

    Recognize that water will flow from a higher level to a lower level with gravity.

    Any restrictions to flow will reduce that flow and increase the time for a specific amount of water to flow through.

    The greater the differences in levels, the greater the flow rate from upper level to lower level.

    Once equilibrium is achieved (levels are equal), there will be minimal potential to no flow.

    To move water from a lower level to a higher level, will need to exert force and work (a mover such as a pump to "push" the water to the higher level).

    I hope this helps.

    Joseph Crisologo
    Senior Homeland Security Engineer
    State of CA, State Water Resources Control Board
    Glendale CA

  • 9.  RE: El Salvador water flow question

    Posted 04-13-2016 12:01 PM

    The short answer, making a few assumptions, is to put a valve on the pipe leading to the houses in the valley.  Close this valve at night so that Tank #2 fills up.  Open the valve during the day to give water to the homes in the valley. Put this valve in a lock box to prevent tampering.

    I've spent years living and working on water systems in the developing world.  In the developing world you have to assume that most water points will either leak or be left on - effectively bleeding all the pressure out of the system.  Water will always choose the path of least resistance.  In this case it will flow to the lowest houses and not to Tank #2.  The most effective way to restore pressure to a point where you need it is to turn off the supply to those who don't need water at that moment.

    If you have the time, resources and knowledge you would conduct a survey of all points along both water lines and draw a hydraulic grade line (HGL) along each pipe.  Keep in mind the fact mentioned above about leaks/taps left on when you do your analysis.  You'll be most interested in the HGL at the point where the "T" is that supplies water to tank #2.  Check out Thomas Jordan's book "A handbook of Gravity-Flow Water Systems" if you need info about how to draw a HGL.


    Dave Holland, PCV

    Haiti 03-04

    East Timor 04-06

    David Holland P.E., M.ASCE
    Environmental Engineer
    Rapid City SD

  • 10.  RE: El Salvador water flow question

    Posted 04-13-2016 12:01 PM

    I am a retired professor and will be pleased to volunteer my time and assist in providing an optimal solution to this hydraulics problem. From my experience in teaching hydraulics, I believe the best approach in this case would be to develop a simple user- friendly spreadsheet that can be used to simulate various water supply/demand scenarios and help examine strategies to distribute the water by gravity more effectively and equitably.

    As previous responders indicated, the first step is to obtain basic data on topography supply/demand parameters, including reservoir capacity, pipe diam and length etc...

    All the best,

    Raouf Emile Baddour, M.ASCE
    Professor Emeritus & Hydraulics Consultant

    Raouf Emile Baddour P.Eng, M.ASCE
    Professor Emeritus

  • 11.  RE: El Salvador water flow question

    Posted 04-13-2016 02:46 PM

    Is there a way to construct a 3rd Tank on Hill #2 ? Supply water to Tank #3 by a connection from line #1 via the shorter ridge line. Increasing the total volume of water on Hill #2 with Tanks #2 and #3 may help solve the temporary situation.


    Hasan Mushtaq, P.E., Ph.D., CFM, M.A.S.C.E

    Floodplain Manager

    City of Phoenix, Arizona

  • 12.  RE: El Salvador water flow question

    Posted 04-15-2016 01:00 AM

    Both pipes will fill and flow, including the existing one going down into the valley and the new one leading to Tank #2 directly.  Its difficult to say how much flow you’ll get in the new pipe without knowing elevations, distances, pipe diameters and types, and demand rates, but it should be an improvement over sending water down into the valley and then up the slope to the second tank. Your friction losses should be less (depending on diameter of your new pipe), and the flow should be more consistent.  The flow will be more a function of the water surface level in Tank #1 versus the fluctuating demands down in the valley, and as long as you have sufficient head, you should be ok.  Valves to control and throttle the water based on demand will help.  Recommend that you send more details if you would like a more definitive answer.  Perhaps you can sketch out a profile view with the items listed above and send that out.  Include elevations, distances, material and diameters of transmission lines, and demand info.

    One other thing, depending on how your new line feeds into Tank #2, you may need a backflow preventer on that line. The last thing you want is for that new tank to empty out by reversing direction in your new pipe and feeding the valley instead of your further out customers.

    Best of luck,

    Christian Manalo, P.E., BCEE

    Booz Allen Hamilton

    Christian Manalo P.E., Dipl, M.ASCE
    Booz Allen Hamilton
    Fort Washington MD
    (703) 377-1697

  • 13.  RE: El Salvador water flow question

    Posted 04-18-2016 09:39 AM
    Christian's response is the most complete I've seen.  I'm traveling so I haven't replied sooner.  The system geometry, pipe type/diameter, and connections are necessary.  A hydraulic analysis can then be made to optimize the solution. Be sure the system advises of any special fittings and their locations (tees, valves, reducers, etc.).

  • 14.  RE: El Salvador water flow question

    Posted 05-18-2016 09:35 AM

    If I understand your description, water flows from tank #1 to tank #2 through a pipe that connects to the distribution pipe from #1. The houses on the "far" side of tank #2 do not get water for the entire day. You want to increase the availability of water to those houses. You are limited by the tank #1 outlet pipe to a certain amount of flow.

    I assume (dangerous word) that since tank #2 is lower than tank#1, there is some kind of float valve which will cut water off when tank #2 is full.

    It appears that demand exceeds the capacity of the outlet pipe. When that happens, the water from tank #2 probably drains back into the inlet pipe back to the valley, draining tank #2 to the point that it cannot supply the houses outside the valley. During the night, tank #2 recharges from tank #1. If this is the case, an additional recharge line may not solve your problem.

    Try putting a backflow preventer on the inlet to tank #2 so that water cannot drain back into the valley. You could also put satellite tanks at each house outside the valley so that they recharge during the night and provide adequate water during the day. Plastic tanks are pretty inexpensive.

    Casey Elliott, PE, PS
    London OH