Plumbing Full course part 31

In this part of the Full Plumbing Course, we will learn about Stormwater / Rain water system design in Plumbing.

Rainwater/ Stormwater System Design

The term storm water refers to the flow of water caused by rain, snow, and wind. If not managed properly, these flows of water can cause flooding, erosion, and pollution in our urban ecosystems. A storm drain system absorbs excess water runoff from impervious surfaces such as parking lots, rooftops, driveways, and streets. These drains carry the collected water away from city streets and to local streams, creeks, rivers, lakes, or wetlands. In order to create a safe drainage system, there are several factors we need to consider. We have to identify the location of each storm drain, its size, orientation, slope, depth, and type of material(s) used in construction.

How do rainwater systems work?

A rainwater harvesting system (RWH) collects rainwater that falls on rooftops and then stores it away in cisterns. The stored rainwater is used for domestic purposes, garden irrigation and flushing toilets. RWH reduces the reliance on groundwater and prevents contamination of surface water bodies.

Design considerations

The size of the cistern should be determined depending upon the amount of rainfall received by a particular location.

How to install a rainwater harvesting system?

Cisterns need to be installed above the roof line and preferably not below it. Cisterns may be attached directly to the gutters or may be attached using small pipes called down spouts.

Advantages

It provides potable water for drinking, cooking and washing, with no chemicals added.

It saves money spent on buying bottled water.

It helps protect the environment.

It keeps a constant supply of fresh water at home.

It is a simple way of conserving water.

Disadvantages

It requires space and construction expertise.

In this article we'll go over rainwater collection systems along with some basic information about how they work. We'll start off discussing the basics; then move onto some different types of designs and their pros and cons. After that we'll cover some additional things to consider like storage tanks and filters.

A typical rainwater collection system consists of three parts: 1) A downspout 2) An underground pipe or tank (or both), and 3) A catchment area where the collected runoff empties into the tank. There are two general types of downspouts: gravity/force-fed and pressure-driven. Gravity/force-feed systems use gravity to carry water away from the roof. Pressure-driven systems force water with high pressure out of the downspout using a small pump. When the water falls from the roof on a relatively steep pitch, the weight of the water causes it to fall faster than if it were falling on a flat surface. As a result, the pressure difference between the top and bottom of the downspout increases. Since water at higher pressure tends to flow more easily, the water flows out of the downspouts much more rapidly. The amount of water flowing out of the downspouting pipes varies depending on the height of the roof and the slope of the roof. In theory, the water will collect enough in a short time to fill a holding tank.

There are many advantages to installing a rainwater collection system. Foremost among them is the fact that a well-designed and installed system will provide several years of continuous service. If properly constructed, the collection system should not require maintenance for this period. Second, a properly designed rainwater collection system eliminates the need for potable water treatment facilities. Third, the installation of a rainwater collection system provides homeowners with the opportunity to generate electricity from the movement of water. Fourth, rainwater harvesting helps reduce the quantity of stormwater that enters local streams and rivers. Finally, a rainwater collection system is aesthetically pleasing.

The primary disadvantages of rainwater collection systems include the expense of installation. As mentioned above, a well-designed rainwater collection system can last for several years without requiring maintenance. However, the initial cost of the system may be prohibitively expensive. Another disadvantage is the difficulty in finding a convenient location for the collection system. Once the system is in place, it takes up space. This means that the area around the building must either be modified or sacrificed to accommodate the rainwater collection system.

Rainwater systems are often overlooked in comparison to irrigation systems due to the amount of time and money spent installing them. However, they have some unique advantages over conventional irrigation methods.

Designing rainwater systems requires planning for several different variables. First, you need to determine how much water you want to collect, whether you live in a rural area where rainfall is abundant, or if you live in a city where the weather is unpredictable. You also need to consider how much water pressure you require and what kind of pipes you plan to use. Finally, you should decide where you will install your collection system (pond, cistern, tank) and where you will release it (gutters, downspouts).

The first step is to lay out the location of the catchment area. In this case, the site was chosen based on its proximity to a natural spring and proximity to a well pump outlet, both of which would help facilitate siphoning off storm runoff. Next, take measurements of the pipe sizes needed to transport water from the catchment area to the house and from the house to the garden using a tape measure and a level. A simple calculation will show how many gallons of water a week you could expect to capture. Once you have determined the volume of water you want to collect and the size of pipes you need to transport it, you can calculate the cost of building and maintaining your rainwater system.

Stormwater runoff is the amount of water that flows off pavement and impervious surfaces (such as rooftops, driveways, parking lots) and enters storm drains and surface waters. Stormwater includes rainwater, snowmelt, and melted ice and may contain sediment, trash, oil, grease, fertilizer, pesticides, herbicides, metals, petroleum products, and many other contaminants.

The majority of pollutants entering waterways originate in urban areas, where land use patterns have led to excessive amounts of impermeable surfaces and impervious objects. A lack of understanding about how the city's storm sewer system works often results in people not being aware that their property is contributing to the pollution of our streams and rivers. The goal of stormwater management is to reduce pollution of local bodies of water resulting from human activities.

It is important to understand the difference between stormwater and wastewater. Wastewater is sewage that is piped away from homes and businesses. Stormwater is rainfall that runs over streets, parking lots, roofs, sidewalks, etc., and then goes down into catch basins and gutters. The flow direction of water going down a street is called flow-direction; this means that the rain is coming directly from one side of the road and is flowing towards the curb.

A pipe is installed beneath the ground to channel the stormwater to the nearest public sewer line. In most communities, the pipes are buried underground at least three feet below the grade. These pipes are connected to various devices that allow them to collect and transport stormwater from different locations throughout the community.

Stormwater Management Plan

A stormwater management plan (SWMP) is a document that describes the actions taken to manage stormwater quality and quantity. It outlines what the community is doing to prevent erosion problems, what they are doing to prevent polluted water from making its way into the receiving stream or river, and what they are doing to make sure that polluted water does not enter the drinking water supply. In addition to describing how these things are done, the SWMP should describe any proposed changes, including those that would increase or decrease the pollutant load in the receiving waters.

There are two parts to an effective stormwater management program: prevention and control. Prevention involves reducing the volume of stormwater runoff that makes its way into the storm drain before it reaches the system. Control encompasses everything after the stormwater reaches the system. Here are some examples of ways to reduce the number of pollutants that reach the storm drain before reaching the facility: reducing the speed of vehicles traveling on roads; increasing the permeability of soils and paving materials; planting vegetation along roadsides and around buildings; and installing rain gardens.

Other measures that help keep the water cleaner once it gets to the treatment facility are included in the control section of the SWMP. Examples of controls include using filters on sewer connections and other piping systems; using screens and grates to keep debris out of the system; and treating sewage with chemicals. In order to determine whether the facilities in your area need better maintenance, call your local county building department or contact the state Department of Environmental Quality to find out if you need to file an application.

Stormwater Pollution Sources

Sewage—Sewage enters the stormwater drainage system either directly from houses, businesses, or industry that discharge untreated sewage into the storm drain, or indirectly from septic tanks or cesspools.

Industrial discharges—These discharges occur when industrial operations release pollutants directly into the storm drain. These pollutants include motor oil, solvents, cleaning fluids, paints, detergents, and many others.

Vehicular traffic—Heavy vehicle volumes cause heavy loads of sediment to be carried along roads. Sediment can block storm drains, causing flooding problems.

Oil spills—Large quantities of crude oil or asphalt can clog a storm drain. Oil that is discharged into the storm drain can damage the equipment used by wastewater treatment facilities.

Trash—Garbage bags, diapers, cigarette butts, plastic bottles, paper, Styrofoam cups, and Styrofoam food containers all contribute to the pollution problem. Cities require residents to separate garbage from recyclables. Garbage must never go in the storm drain.

Stormwater design in plumbing is basically a system of pipes, tanks, and pumps designed to capture and store rainwater runoff before releasing it either to the public storm sewer or back into the ground water table. Storm drains are designed primarily to remove surface water from streets and parking lots while retaining the greater volume of rainfall and filtering out small particles from the water. Storm drainage systems are also used to collect water entering buildings, and then discharge this water outside via a downspout. Downspouts allow excess water to flow away from building foundations, preventing erosion and flooding.

The most basic type of storm drain consists of a pipe about 6 inches in diameter, called a riser pipe, placed below grade and extended as high as possible. Risers are commonly installed at depths ranging from 2 to 20 feet (0.5 to 6 m). A manhole cover may be located where the storm drain enters the street to prevent people from falling into the storm drain, and may have a grate over it to keep debris from entering the storm drain.

A rain garden is a planted area designed to filter, soak up and infiltrate stormwater runoff before it flows into nearby waters. Rain gardens use natural vegetation and soil-based filtration mechanisms to cleanse water of pollutants before it reaches bodies of water. Typically they are constructed in an open space adjacent to a home's driveway, lawn or other paved area. Their placement may take advantage of existing topography to maximize infiltration of rainwater. A rain garden should be planted with native species adapted to local conditions. Most rain gardens consist of porous surfaces covered with grasses, shrubs, trees, meadow flowers or even moss, which help to retain and filter liquid runoff. Plants absorb contaminants and reduce odor. Rain gardens are often combined with other methods of stormwater management to protect waterways.

An underground tank is a concrete or plastic container placed beneath the ground and filled with water. Underground storage tanks are used to hold stormwater runoff until it can be pumped to a treatment area. There are three types of tanks: gravity tanks, vacuum tanks, and air spargers. Gravity tanks are simply containers holding water without any means of forcing water to move in them. Vacuum tanks force water to move by applying negative pressure. Air sparging uses pressurized air to create tiny bubbles that break up sediment and bacteria in the water, making it easier to pump. Underground tanks are cheaper than pumping stations, and are commonly used to treat wastewater.

Pumping station collects stormwater runoff from rooftops, driveways, sidewalks and anything else that causes a flood. Cleaned-up stormwater runoff is sent to a treatment facility. Typical treatment facilities include ponds, lagoons, wetlands, or bioretention basins. Bioretention basins are artificial landfills that act as catch basins for stormwater runoff. They are low cost and relatively inexpensive to construct. Conventional detention basins are also low-cost options, although they require more site preparation and construction time. Wetlands are the most expensive option, requiring extensive site preparation and construction time, but they are best suited for highly polluted areas. Ponding works well for smaller sites and requires little maintenance.

Stormwater runoff has been a concern for many years due to lack of design awareness and understanding of storm water management. Stormwater, also known as surface runoff, can carry pollutants from roads, rooftops, parking lots and even construction sites. In addition to carrying these contaminants, stormwater can cause erosion, siltation, flooding and pollution to nearby bodies of water. To help prevent this type of damage, proper stormwater management should be implemented. Many cities have adopted a stormwater ordinance that requires developers to manage stormwater. A good example of this is Toronto's Green Stormwater Ordinance (GSO). GSO provides guidelines for how to properly design and construct stormwater infrastructure while ensuring that they provide the best benefit for public and environmental health.

1. Site Characteristics

Before determining what types of systems are appropriate at a site, there are several factors that need to be considered. First, the size of the project and the surrounding area will determine the number of possible system options. Second, the amount of impervious surfaces present, including roofs, streets, sidewalks, parking lots, etc., will decide if a rain garden or swale system is feasible. Third, the location of the proposed system components may influence the choice between a catchment, detention pond, cistern, infiltration trenches, or some combination of all these elements. Fourth, the existing land use patterns and characteristics will affect whether the site is best suited for a permeable pavement, bioswales, green roofs, or any other type of sustainable drainage system. Finally, site conditions, such as slope, geology, soils, vegetation, accessibility, etc., may limit the opportunities for sustainable drainage solutions.

A site evaluation may be conducted before choosing a suitable solution. If the site already contains natural stormwater management features, then those features can be evaluated and incorporated into a plan. However, if the site doesn't have any natural drainage features yet, then a pre-development site assessment might be necessary to identify where stormwater enters the site and where rainwater runs off after leaving the site. Once identified, the site could be divided into quadrants according to its shape and location. Within each quadrant, different alternatives can be chosen based on the potential for successful implementation. These alternatives include rain gardens, swales, permeable pavements, green roofed tanks, detention ponds, infiltration trenches, underground storage tanks, culverts, and gully systems.

2. Design Considerations

In order to choose the right alternative for sustainable drainage design, information about the site needs to be collected first. This includes the following:

a. Geotechnical Information: This includes information related to soil composition, permeability, slope, hydraulic conductivity, groundwater levels, depth to bedrock, and the presence of unstable slopes.

b. Landscape/Vegetative Cover: Information about the height, density, and species of trees, shrubs, grasses, ferns, etc. will indicate the suitability of using vegetated cover around the site.

c. Existing Infrastructure: This includes information on roads and paths, power distribution networks, sanitary sewer pipes, gas line mains, fire hydrants, water supply utilities, storm drains, parking lots, and any other structures. This will allow designers to determine whether any future storm water management measures would interfere with their operation.

d. Soil Drainage Conditions: Data about the topography, elevation, and moisture content of the soil will give insight into the suitability of applying sustainable drainage techniques.

e. Topographic Features: The presence of steep slopes, high points, low areas, depressions, ravines, waterways, and other physical aspects of the terrain can affect the design of a sustainable drainage system.

Once the data is gathered, a preliminary design can be developed. The type of sustainable drainage system selected will depend on the site's characteristics and will vary depending on the scope of work. The most common options are described below:

a. Rain Gardens: Rain gardens are designed to capture and retain rainfall runoff in order to filter it before releasing it back into the environment. Rain gardens are often installed in conjunction with traditional storm sewers. If the site does not have adequate drainage capacity to handle the volume of rainfall, the rain garden will reduce peak flows by diverting them away from the street.

Rain gardens are constructed using porous materials, such as crushed stone, gravel, or decomposed granite. Perennial native plants are sometimes added to the mix to improve their aesthetic value and to maintain their effectiveness over time. Plants should be placed so that only the root systems extend down into the basin. As the plants die, new ones can be planted in the space left behind.

Stormwater Design Basics

Stormwater is runoff water that accumulates along the ground, especially after rainstorms. Runoff water contains contaminants like trash, oil, grease, fertilizer, pesticides, and heavy metals. These pollutants can cause serious damage to streams, rivers, lakes, and oceans if not handled correctly. When designing stormwater management systems, it is important to take into consideration the following:

- Location – A location where stormwater would accumulate should always be chosen. If you live near a lake or river, choosing a site near the bank ensures that sedimentation does not occur. However, choosing a site close to a drainage system prevents excess flooding and erosion.

- Size – The size of the area selected to capture stormwater should be large enough to handle the amount of precipitation expected over the period of time in question. In some cases, it may be necessary to add additional capacity to accommodate anticipated rainfall totals.

- Surface type/material – The surface material upon which the stormwater runoff will collect should be considered. Most commonly, impermeable surfaces (such as concrete) capture contamination more effectively than permeable ones (like grass).

In addition to these considerations, the age, condition, and quality of existing infrastructure play a major role in determining what kind of stormwater management system is suitable. As a general rule, older buildings have larger systems installed due to their increased complexity and need. Older systems tend to require maintenance and repair on a regular basis, which could prove costly in terms of both money and time. On the other hand, newer buildings usually offer smaller systems that make them easier to maintain and repair.