Open and Closed Water Systems: Applications and Design Equations

There are two main water systems types that are used for most engineering design and calculations: pressurized (or closed) pipes for water distribution and non-pressurized (or open) pipes for water collection.

Pressurized pipes are typically used for water supply, and they get their name from the fact that the pressure for any cross-section along the pipe, the pressure difference between the top and bottom of the pipe does not vary (except for the elevation head). In these types of systems, pressure is lost as water travels along the pipes due to friction. The pressure is typically supplied by a pump or simply by gravity itself, depending on the elevations of the start and end of the pipe.

In contrast, non-pressurized pipes are typically used for wastewater and they get their name from the fact that at least one pipe end is open to the atmosphere and therefore under atmospheric pressure. In these type of pipes, pressure changes both vertically across a cross section and horizontally (also due to friction) as the water travels along the pipes. Under non-pressurized conditions, water will flow from the highest to the lowest elevation as a function of the pipe size, slope, diameter and material.

Three common equations that are used for design of open and closed systems are: Hazen-Williams Equation, Mass Conservation or Continuity Equation and Manning’s Equation. The Hazen-Williams Equation is mostly applied in closed systems and it establishes a relationship between the volumetric flow rate against the head loss, pipe diameter, and the Hazen-Williams Coefficient, which varies depending on the pipe material. The equation gets the name after its developers, and it is commonly used for design of water supply, fire sprinklers and irrigation systems.

The Mass Conservation or Continuity Equation is a simple yet useful relationship that can be used both in open or closed systems. The formula is based on the fact that water is incompressible and the volumetric flow rate going through any point in time must be directly proportional to its velocity and the cross sectional area. Mass is always conserved in fluid systems regardless of their complexity and flow direction. What is also useful about this equation is that it can be used to compare the areas and velocities of two different pipes. When continuity exists, the mean velocities at all cross sections having equal areas are then equal, and if the areas are not equal, the velocities are inversely proportional to the areas of the respective cross sections. This is further shown in Figure 3 below.

Last but not least is the Manning’s Equation, which is the most popular for open water systems. It is used to calculate the velocity of a fluid flowing through a partially full pipe. Once the velocity is known, the flow can be calculated using the Continuity Equation. The equation is based on the fact that the flow through an open conduit is directly proportional to the flow area and slope (or energy loss), but indirectly proportional to the Manning’s coefficient and the wetted perimeter. The Manning’s coefficient is based on the pipe material roughness and is dimensionless

There are plenty of online resources out there that can further complement your reading when understanding how these equations are applied.  You may also reach out to me via LinkedIn to learn more or simply get in touch!

By: Salvador Bentolila, PE, ENV SP
Disclaimer: I do not hold any relationships or affiliations with the companies listed above other than my own LinkedIn profile.

Salvador Bentolila, PE, ENV SP is a Civil Engineer, specialized in Water Resources. He currently works as a Water/Wastewater engineer at AECOM and has experience with design and development of water supply, irrigation and wastewater systems.



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Dampness in building, causes of dampness and effect of dampness.


Dampness is the presence of gravitational moisture into the walls, flooring of roofs, one of the basic provision of the building is that should remain dry free from moisture travelling through building parts like a wall.

Dampness is to reduce the strength of building components.

Dampness prevention is the most part of building or structure design,

Every building should be a damp proofing course.

Provision of damp proofing course is to prevent the entry of moisture into the building structure.

Causes of dampness in building

1. Moisture rising up the walls from ground
2. Rains travel from walls tops.
3. Rain beating against external walls.
4. Condensation
5. Miscellaneous causes.

Moisture rising up the walls from ground

The building is constructed in soil. The substructure is into the ground some depth if the soil is previous, moisture constantly travels through if for impervious soil lots of soil present. The moisture is rise through the wall from substructure to superstructure through capillary action. Rise of groundwater is also the reason for moisture rise into the building through wall and floor.

Rains travel from walls tops.

If the wall top is not properly protected with waterproofing course then the water is entering into the wall from the top of the wall go down. Also, the leakage of the roof is the causes of dampness in a building.

Rain beating against external walls.

During the heavy rainfalls sometimes rains beating against the external face of walls and the walls are not properly treated. Then water is entering into the wall this will cause dampness of interior of the building structure. If the balconies do not have sufficient outward slop then the water is entering the walls from walls junction and it will cause the dampness in a building.


Due to condensation of atmospheric moisture, water is deposited on the walls, floor and roof, this will cause dampness in a building.

Miscellaneous causes.

Improper drainage

Improper drainage at the building site may cause dampness. Because deposit of water around the building the water is rise into the walls and floors through the capillary action.

Insufficient roof slope.

 For flat roof should be provided sufficient slope for the drain of rainwater. Otherwise, the rainwater is entering into the roof that will cause dampness.

Rainwater pipes leakage 

Rainwater pipes leakage from defective rainwater drainage pipe may cause dampness in walls.

Imperfect orientation 

Imperfect orientation if the wall does not get proper sunlight and heavy shower may remain damp.

Effect of dampness

1. Travel of moisture through walls and ceiling may cause unlikely patches.

2. Moisture travel may cause suffering and crumble of plaster.

3. The continuous presence of moisture in the walls may cause efflorescence resulting in disintegration of bricks stones tiles etc. and consequent reduction in strength stones tiles etc, and consequent reduction in strength.

4. Moisture cause rusting or corrosion of metal fitting attached with walls, roofs and floorings.

5. Dampness promotes and accelerates the growth of termites.

6. Electrical fittings get worsen gives rise to leakage of electricity and consequent damage of short circuit.

7. The wall decoration is damaged. this is costly to recover.

8. Dampness creates unhealthy living conditions.

9. Floor coverage damaged on the damp floor are cannot use a floor covering

10. The flooring may lessen due to dampness. Because of dampness reduction the adhesion.



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Top Five Digital Tools Must Buy Civil Engineers

Hello, Every Civil Engineers Welcome To My Blog. Today I Will Inform You Some Digital Devices For Used In Our Civil Engineering  Field. 

This Is Very Valuable and Make Our Works to Simplify.

Line Laser Level Measure Beam

Line Laser Level Measure Tool Is Produced By Bouch -click here to buy-

Technology Improving Every Day Very Fast This Equipment Is Simplified Some Jobs.

Bouch Laser Line Laser Used For Exterior and Interior Horizontal Leveling  And Vertical Alignment.

It Is Used In All Job site Conditions.

It Gives 360 degree Laser Plane Also 90 Degree Angles.

This Laser Extended In All Light Conditions Up To 15 Meters.

It Also Used Slope Works

It Can Be Used To Following Purposes

1.Laying Tiles In Wall In Any Location With Exact Right Angles Without Using Of Any Other Devices.

2.Laying Cupboards And Shelves.

3.Laying Floor Skirting With Good Alignment.

4.Instilling Electrical Sockets.

5.Mounting Windows and Doors Frames.

6.Mounting Windows and Doors Frames.

7.Fixing Hand Rails In Staircase With Good Angle.

Laser Distance Measuring Meter (Leica Disto X3 Laser Distance Meter )

This Device Is Used To Measure The Distance between The Objects With The Help Of Laser Dot.
You Have To Measure From A Very Narrow Profile Notches, Corners.
You Can Also Measure the Diagonal.-click here to buy-

Laser Line Sprit Level

This Is Very Attractive Tool, It Can Be Used For Every One Like Engineers, Mason, carpenters  Etc.

This Tool Is Used To Check The Sprit Level Of Any Surface, Also For In Knight Time. It Has Inbuilt Led.-click here to buy-
This Device Also Have Inbuilt Of Measuring Tape And Horizontal As Well As Vertical Laser Lines
 For Accurate Measurement.

You Can Fix The Parallel Point Of Any Compared Surfaces With The Help Of Laser Line Points.

Digital Angle Finder

Digital Angle Finder Is Very Cheap And Efficient Tool.-click here to buy-

That Can Be Used To Set Angle Of Any Object Like You Can Mark The Line Of A Wall In Any Angle.

It Is Must Used For All Architects And Masons For Mark The Angle For Any Architect  Works.

Mini Bubble Sprit Level.

This Is The Very Small And Efficient Tool, It Can Be Carry With In Pocket Of All The Times
This Small Bubble Tube Is Used To Check The Surface Alignments, Door Alignment, Window Alignment -click here to buy-


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