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Thread: Tanks vs Reservoirs

  1. #1

    Question Tanks vs Reservoirs

    The following are water sources for our system:

    Above Ground Tanks
    Groundwater Wells

    Can these all be placed in a RESERVOIR Feature Class or does InfoWater require them to be separated into a TANKS and RESERVOIR Feature Class?
    Tim Hayes
    GIS Manager
    City of San Jose Municipal Water System
    San Jose-Santa Clara Regional Wastewater Facility

  2. #2
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    Tim,

    While people often interchange a "reservoir" and a Tank for what a storage device in the water system is called, in the model they have very specific definitions.

    A Model "Reservoir" is a water source (or sometimes can also be a water "sink" that can receive water, although that type of use is more rare.) These can supply an infinite amount of water supply and are commonly used to represent supply from groundwater source for a well, a WTP treatment stream, a water source for a purchase water connection or emergency connection. These is not always a definable GIS element that can represent these locations within a model, and they often have to be added by the modeler when constructing the model to provide water supply that will be used to satisfy model customer demands.

    A Model "Tank" represents a storage device that can fill and drain, but that has a limited volume of water that can supply water demands or that can fill up when supply exceeds demand. Model Tanks generally do have a specific GIS element that is used to represent them as these are actual water storage devices in the water network. When there are multiple tanks at the same site, this can cause some instability mathematically in a hydraulic model as it runs, especially if you are doing an Extended Period Simulation (or EPS) that are usually in some multiple of 24 hours in length. In those cases, modelers often will combine the area for all Tanks at the site into a single tank with an equivalent diameter as this is much more stable in the model solver. In that case you may either choose one of the tanks to represent all others or you may have a "dummy" tank that is used to represent the combined area of the tanks.

    As the model builder you would need to decide which elements would be assigned to each type based on what the elements represent.

    Here is some additional hints on how to set up a model Tank:

    In the model a storage device or Tank has a few key parameters you generally always need to set


    1. Tank Type – < >Cylindrical– Use cylindrical if the area per foot is constant whether the tank is round or rectangular/square with an equivalent diameter is needed. It is often most stable to combine all tanks at a site into a single equivalent tank Just think Area = pi/4*D^2 and solve for the equivalent diameter for the combined area if needed.Variable Area – Use if the sides slope or change the volume per ft of tank at a variable rateIf you are unsure of the units set the curve as Volume-Depth type and based on your Input units in the simulation options it will set it to the right units you need.
      1. For L/s flow and M for pressure the units are Depth (M) to Volume (M^3)
      2. Volume Depth Curve Type (click if need larger image)Tank Volume Curve.jpg
      3. For gpm flow and psi Pressure flow units this curve is Depth (ft) per Volume (ft^3)

    Tank elevation – This is the bottom of the tank HGL (unless you specify a minimum Level for the tank and that would override this value.)
    Max Level – The is the highest level the water can get to in the tank (this is the 100% full level in the tank)
    Min Level – Not required but will set the 0% full (i.e. empty) level of the tank
    Initial Level – The level in the tank at the start of any simulation
    Diameter – The tank Diameter when cylindrical type
    Curve – The volume Depth curve if Variable area

    Please note that any controls using a tank should avoid using either the min or max level in the tank in control statements as these generally would not work properly.

    If Tank is Rectangular
    If you have a rectangular storage where the area per ft of water is constant just convert it to an equivalent circular tank.

    Area of Square = L*W
    Area of Circle = pi/4*D^2

    Set these equal to each other and solve for D

    Pi/4 *D^2 = L*W
    D = sqrt( L*W*4/pi)

    If the Tank has sloping sides then you will have to Set it as a Type of Variable Area and use a Volume (in ft^3) per ft curve, where the volume is the cumulative volume as the height increases.

    Patrick Moore


    Quote Originally Posted by sewermapguy View Post
    The following are water sources for our system:

    Above Ground Tanks
    Groundwater Wells

    Can these all be placed in a RESERVOIR Feature Class or does InfoWater require them to be separated into a TANKS and RESERVOIR Feature Class?

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