Detailed Duplicable City Center water catchment

Duplicable City Center Water Catchment

Welcome to the Duplicable City Center water catchment hub. As part of our global transformation approach to Highest Good housing, we are using this page to share the complete design, construction, storage, and ongoing maintenance and upkeep details of the Duplicable City Center water catchment system we are designing.

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DUPLICABLE CITY CENTER WATER CATCHMENT

Duplicable City Center Water Catchment Icon, water conservation methods, advantages of rainwater harvesting, rainwater harvesting techniques, open source water systems, methods of rainwater harvesting, smart water, intelligent water use, swails, One Community, solution based thinking, conserve water, water conservation, water wise, saving water, best land for water, mulch, water catchment, water collection, swails, water collecting, vermiculture, conserving waterThe Duplicable City Center will be a totally sustainable and eco-friendly building. One of the tools that we can use to make that possible is implanting a system of rainwater harvesting and reusing water as much as possible. Water will be collected off of the entire Duplicable City Center. Water catchment for this area has been calculated using the following color coordinated zones: Pink for the domes and Blue for the central area. There is a 4th-floor cupola that will cover the central area but water will still be collected from this cupola so we have used the zones you see below for simplicity.

Duplicable City Center Water Catchment

Duplicable City Center Water Catchment Zones

WATER CATCHMENT OFF THE THREE DOMES (PINK)

The Duplicable City Center footprint for each of the domes (area of the circle) was calculated for rainwater catchment. The area of a 74′ diameter circle equals 4,300 feet x 3 domes = 12,900 sq ft. Using a (conservative for our location) 10-inch annual rainfall* and applying the formula for calculating water harvesting (catchment area x rainfall x runoff) yields: (12,900) X (.833) X (7.48) = 80,485 gallons of water harvested per year from the domes.

Note: For those interested, the actual surface area of each of the Duplicable City Center’s 74′ diameter/35′ high domes (pink) can be quickly calculated using this tool as equalling 8,149 feet.

WATER CATCHMENT FROM THE CUPOLA AND CENTRAL AREA (BLUE)

The area of the central water collection zone (blue) for the Duplicable City Center includes the area shown on the map above (topped with the cupola that will cover much of this area) equaling roughly 3,010 sq ft. of rain collecting space. Using a (conservative for our location) 10-inch annual rainfall* and applying the formula for calculating water harvesting (catchment area x rainfall x runoff) yields: (3,010) X (.833) X (7.48) = 18,754 gallons of water harvested per year from the Duplicable City Center Hub.

TOTAL WATER CATCHMENT FOR THE DUPLICABLE CITY CENTER
99,240 GALLONS OF WATER

*Note: For calculating cistern and pond sizes we used the average annual rainfall for our location of 13.6 ~ 15 in = average of 368.3 mm. For calculating pipe size we used the Daily Critical Rainfall (the maximum daily amount of rainfall in our location) of 1.3″ / 33 mm.

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KEY CONSULTANTS TO THE DUPLICABLE CITY CENTER KITCHEN

Mateus Moura BarrettoCivil Engineering Student specializing in Hydraulics

CITY CENTER WATER COLLECTION
DESIGN DETAILS

Here is an overview of the piping for the collection, transport, and storage of rainwater from the City Center:

Initial-Design-of-the-collect-system

Design Overview

To design the system we started with the maximum amount of rain that could be experienced for our location. Figure 1 below shows a diversity of different areas:

Rainfall Intensity Chart, One Community

Figure 1 – Click to View PDF

For our our location, the number we’re concerned about is 1.3 in.

 

SIZING PIPES

Next we needed to size the pipes and choose the slope. Referencing the International Code Council, this is the table we used for drainage pipe installation.

Screen Shot 2015-05-08 at 7.37.14 PM

The slope of ¼ was chosen because a 2.5″ pipe will be sufficient for rainfall in our area. 

DISCHARGE RATE:

Next, we used the information above to calculate the discharge rate:

  • Catchment area = 15,910 sq ft
  • Daily critical rainfall in our location = 1.3 in
  • Runoff Coefficient: 0.95 (equal to downtown areas with little or no permeability)
  • 15,910 sq ft x 1.3/12 ft x 0.95 x 7.48 gal/cu ft = 12,248 gal of water in a critical day
  • 12,248 gal of water / 8 drains : 1,531 gal of water per drain.
CHOOSING THE TYPE OF PIPES

The material with the best cost x benefit ratio is PVC because it is light, durable and not expensive. The roughness (friction loss) coefficient of the PVC is 150.

PIPES DIAMETER

Using factors such as flow rate or discharge, Hazen Williams’ friction coefficient, and hydraulic grade line slope, it was possible to calculate the diameter of the pipes. For the initial catchment water, we will use a total of 8 drains with a diameter of 2.5 inches to guarantee that no water will be wasted.

 

SIZING DOWNSPOUTS

Referencing this Uniform Plumbing Code table with our 1.3″ maximum anticipated rainfall within a 5 minute period (Figure 1 above), and knowing the total area of the water collection is 15,910 sq ft., we chose 4 downspouts to cover the areas not covered by ground-based gutters. Calculating these areas meant each downspout will be responsible for an area of approximately 1,989 sq ft. The rest of the water will flow off the domes and be transported via ground-based gutters to drains. 

Screen Shot 2015-05-08 at 7.21.07 PM

In our case, a 3-inch downspouts will be totally sufficient for our purposes. We will only use a total of 4 downspouts because the gutters installed around the base of the domes will handle most of the water. Here is a picture of the downspouts and piping from the drains:

Screen Shot 2015-05-08 at 7.24.05 PM

Length of Downspouts:

  • Point A and E: 25’
  • Point 5: 45.5’
  • Point 1: 37’

Here are the specific pipes diameters and lengths:

Screen Shot 2015-05-08 at 7.25.05 PM

 

SIZING GUTTERS

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Considering that the water flowing inside the gutters can be considered as an open channel flow, the best option to calculate the best size for the gutters is using the Manning Equation. This equation is a function of the channel velocity, flow area and channel slope. The following table shows Manning’s Roughness Coefficient:

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By applying the Manning Equation in our project we conclude that the best solution is use 6” k-style seamless PVC guttering.

Total Length of Gutters:

182′ + 162′ + 181′ + 116′ + 192′ = 833 ft

FIRST FLUSH OF WATER

For health reasons, it is important to address the first flush of water. When it rains, water slowly builds up in the roof gutter system before it exits through the downpipe. The first flush of water from the roof can contain amounts of bacteria from decomposed insects, lizards, bird and animal droppings and concentrated tannic acid. It may also contain sediments, water borne heavy metals and chemical residues, all of which are undesirable elements to have in a water storage system.

There are many systems to flush off the first flush of water, but one of the smartest and economical systems to use is a dependable ball and seat system. This is a simple automatic system that does not rely on mechanical parts or manual intervention. As the water level in the diverter chamber rises, the ball floats, and once the chamber is full, the ball rests on a seat inside the diverter chamber preventing any further water entering the diverter. The subsequent flow of water is then automatically directed along the pipe system to the tank. Here’s what this looks like:

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SIZING CISTERNS

A cistern should have sufficient storage capacity to carry the household through extended periods of low rainfall. A three-month supply of water, or one-fourth of the annual yield of the catchment area, is generally adequate in areas where the rainfall is distributed fairly evenly over the course of the year.

The figure below illustrates this idea. For example, if you have determined your annual domestic water needs to be 40,000 gallons (and, most importantly, you have enough catchment area and annual precipitation to supply this amount of water), then you should design and build a cistern with a 10,000-gallon storage capacity.

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Considering that our location has fairly even rainfall distribution over the course of the year, and knowing that the total water catchment for the Duplicable City Center is 99,240 gallons of water for the year, we chose to adopt a cistern of 25,000 gallons (3,345 cubic feet).

In this situation the best solution would be to split this by constructing two cisterns whose dimensions are:

  • Diameter: 11 ft
  • Height: 18 ft

Cistern volume: π x 5.5² x 18 x 2 = 3,421 cubic foot

Final Design of Rainwater Harvesting System:

  • Yellow Pipe: 2.5” (diameter)
  • Blue Pipe: 3.0” (diameter)
  • White Pipe: 3.5” (diameter)

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RESOURCES