Background:
Urbanization:
As the world’s population grows the increase of people moving from the country to urban areas also increases. Urban areas are dense spaces with tall building being erected to utilize the limited amount of space to work with. Presently half the world’s populations live in these urban areas, cities of millions of residents compacted and compressed. Urbanization and surface runoff become a potent combination in the decrease of water reaching soil. The majority of urban areas consist of concrete found in buildings and infrastructure such as sidewalks and highways. Concrete is an impervious surface which does not allow percolation of the water runoff back into the soil. Water runoff is then redirected into the grates of sewers which move the runoff inevitably to a stream or river which contributes to the erosion of these channels. Urban development also causes soil to be compacted to the point where it can become impervious to water.
Challenges of Urbanization:
Impervious surfaces are created in the majority of urban areas. Because of this increase of impervious materials, surface runoff is prevalent. Urbanization includes the laying down of various forms of pavement and the construction of buildings which are impervious to water and contribute to the slowing down of absorption into the soil. Because of impervious surfaces the increase of water runoff into channels, streams or rivers lead to soil erosion. With a lack of water being absorbed into the soil, the impacts of droughts may be intensified by the lowering of the water table. Flooding also occurs when runoff systems are overwhelmed. Runoff patterns on surfaces have been strongly impacted by urbanization across the globe. “With urban growth and development there is an increasing need for flood information and techniques to evaluate effects of urbanization on flooding in areas where few or no data exist.”.2
Permeable Surfaces:
Permeable surfaces include surfaces which absorb water and impact the amount of run off by reducing it. Permeable surfaces include ones which are connected to nature like plants, grass, flower beds, gravel and landscape. These surfaces allow water to seep into soil which contributes to the removal of pollutants. Figure 1 is of Edwards Elementary soccer field adjacent to the school as an example of a pervious surface which supports runoff and promoting absorption into the ground via the permeable artificial turf.
Figure 1: Edwards’s soccer field an example of a pervious surface
Impermeable surfaces:
Impermeable surfaces do not water to absorb into solid surfaces, which leads to water runoff. These surfaces are known as impervious and include pavements, concrete and asphalt. Examples of pavement can be found everywhere right outside our front door and include driveways, sidewalks, roads, and parking lots. Impermeable surfaces are also materials which are made to be water-resistant such as brick, stone and materials used for rooftops.
The impact of Impermeable surfaces:
A critical factor involving urban areas is its reliance on impermeable surfaces. Concrete and pavement are impermeable and everywhere in the city the landscape is dominated by these surfaces. A great number of problems arise from this including water runoff being polluted as it flows into sewer drains. Some of these pollutants inevitably reach into and carried by streams, rivers, lakes and oceans. This heavy runoff can contribute towards erosion within these bodies of water. During heavy rainfall the water runoff that is produced while flowing over impermeable surfaces can overwhelm storm water collection systems and cause major flooding. Another impact of impermeable surfaces is that it doesn’t allow the water table to recharge itself. With the majority of storm runoff being directed into the grates of sewers, this runoff is directed away from the ground impacting the amount of water reaching the aquifers. A common concern in the city and a source of great irritation are the formations of water puddles which congregate and flood streets and street corners. In the summer these puddles add to an increase of insects including mosquitos that are vectors for disease. Impermeable surfaces affect the environment because it changes the makeup of the surface landscape. From swaths of nature and greenery being replaced by lots of concrete and pavement the resources of water and air are changed. The materials used in the making of impermeable surfaces such as pavement seal soil surface, like a lid over a pot. This impact is felt throughout the entire country. In areas in the Northwest part this from the Seattle Times: “While urban areas cover only three percent of the United States, it is estimated that their runoff is the primary source of pollution in 13% of rivers, 18% of lakes and 32% of estuaries.” Impermeable surfaces act as a carrier of a wide assortment of pollutants including fertilizers and their excess nutrients; pet waste and their pathogens; fossil fuel products such as oil, gasoline from automobiles. In some municipalities the excess of water runoff compromises sewer systems leading to overflow and discharge into other forms of water ways such as streams and rivers carrying pollutants along with the runoff. Ultimately, the runoff of excess storm water impacts the environment in the form of how it effects plants, animals, fish and the human community overall. In Chicago’s developed land, a variety of issues occur from the problem of storm water runoff. Extra runoff can contribute towards the basements of homes and streets getting flooded. The quality of water in the Chicago River can be impacted by the release of runoff from storms. With the construction of man-made structures like roads and buildings adds to the impact humans are making on the planet. These structures have impervious surfaces which shift water runoff away from the water table and into sewer systems which carry pollutants into other sources of moving water. “Urban storm runoff is becoming a substantial source of surface-water pollution in the United States. Because collection and analysis of urban-storm-runoff data are expensive and time consuming, city planners and engineers need techniques to make estimates where minimal or no data exist”.4 Overland flow is the buildup and collection of runoff water over surfaces. Watersheds involve the flow of water runoff directly into a specific point over land area.
Peak Runoff Rate:
A Unit Hydrograph can be used to measure the peak runoff rate Q, the amount of runoff over a period of time where it collects in certain point to the amount of rainfall. Each storm in itself determines the information found within the graph with the measurements of total rain being used as data. By using probability and statistics this information can be used to help the possibility of rainfall in future events and where these events may occur as data continues to be collected from storms, these aids in the prediction and forecasting of storms.
Direct Runoff Formula:
Students can determine the amount of water from rainfall using basic calculating methods. By using a direct runoff formula (in in3) students can determine runoff by using the operation of multiplication and multiplying the inches of rainfall by the area of a roof. Run off rate (Q) is equal to the precipitation of an area, minus losses, which are mostly infiltration into soil.
Water Management and Treatment:
In Chicago the city’s water management system links residents across the entire city and outlying municipalities. On a daily basis this system directs approximately one billion gallons of water. In addition, Chicago’s elaborate and complex sewer system is used to handle runoff from storms and waste water, i.e. combined sewers. The city’s aim is to protect the priceless resource of drinking fresh water found in the Great Lakes which Lake Michigan representing the second largest by volume of all the Great Lakes and the only one which is completely located within the boundaries of the United States.
Solutions in Natural Landscaping:
As the class investigates the physical landscape of outside the school we begin to discover the natural landscaping which is present. The students begin to identify and categorize between pervious and impervious surfaces in relation to the various examples of vegetation surrounding the school’s perimeter. The use of vegetation within a surface is referred to as natural vegetation. Landscape area with vegetation will produce less water runoff than a traditional landscape. This vegetation helps in absorption into the soil and the evaporation of runoff from moist soil. Natural landscaping can make runoff improve when on surfaces which are impervious while this specific type of landscaping assists in the removal of pollutants from runoff. The following are a number of examples of natural landscaping.
Permeable Alleys:
This alley in the city is composed primarily of gravel and helps in the use of permeable surfaces rather than impermeable surfaces. Runoff would absorb into the ground through the gravel limiting water runoff into the sewer systems and help in limiting local flooding, see Figure 2.
Figure 2: Permeable alleys
Permeable Paving:
There are materials generally associated with impermeable surfaces such as concrete, plastic and stone that can help in the absorption of runoff. This surface is known as permeable pavement which has openings which have soil and sand. With storm runoff the openings trap water and allow absorption into the soil underneath.
“Green” roofs:
Engineers and architects are including “green” roof design into building to help with water runoff. From schools to office buildings green roofs are becoming popular while addressing some of today’s environmental issues involving water runoff over surfaces which are impermeable. A green roof uses a layer of natural vegetation as a way of storing and filtering out via the roofs soil and plants. Passing through this layer of vegetation, the movement of water runoff is slowed helping in the process of cleaning the water while keeping it cooler. The vegetation of these roofs can help with keeping buildings cooler in the summer and reducing the cost of heat.
Drainage swales:
One way of moving and temporary storing rain runoff is by using a natural channel of vegetation called a swale. Swales also can promote the filtering of pollutants. Swales can be another option besides the use of storm sewers to move runoff quickly from impermeable surfaces.
Downspouts Rain Barrels and Cisterns:
In urban areas run off from roofs can be directed by downspouts into sewer systems. But a better option is to redirect run off from roofs directly into areas of grass and soil. Downspouts from roof tops can direct rainfall into rain barrels and cisterns to be stored temporarily. During small storms rain barrels can hold and store rain runoff. Rain barrels can be effective in storage volume in comparison to the size of the roof. An example of this, a 1,200 square foot roof could utilize 55-gallon cisterns to hold runoff from the roof of the house. The resultant storage is equivalent to about 0.3 inches of runoff. See Figure 3 for an image.
Filter strips:
Filter strips help in the runoff from surfaces which are impervious. The function of these strips is to slow down the movement of runoff and help in water absorption into the soil. See Figure 3 for an image.
Naturalized Detention Basins:
In a conventional detention basin design flooding is prevented by temporarily storing run off from storm water and discharging it slowly into drainage systems. Naturalized detention serves many things including the removal of pollutants, the prevention of floods, and the support of wildlife. At the edges of the water flat slopes are incorporated. See Figure 3 for an image.
Figure 3: the following are different projects of water conservation which can be used to manage storm water runoff. Top left is a bio-infiltration system called a swale. Top right is an example of a downspouts being used with rain barrels and cisterns. Bottom left is an example of vegetated areas known as filter strips. Bottom right is an example of a naturalized detention basin.
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