As water becomes scarce, some cities are changing how they deal with stormwater.
Arid and
drought-like conditions affecting different regions across the US are forcing
many cities and municipalities to change the way they deal with stormwater
management and water reuse. As water scarcity becomes serious, more and more
water professionals are recognizing the value of rainwater and stormwater and
are beginning to adopt and implement progressive strategies for catchment and
retention.
Tucson, AZ
In the arid Southwest,
an eight-year drought has significantly drained Colorado River reservoirs,
including Lake Mead, the largest reservoir in the nation. In January 2000, Lake
Mead had 96% capacity. Two years ago that capacity fell to 51%, and the Senate
Energy and Natural Resources Committee has warned that the lake could go dry in
10 years.
In addition to the
Colorado River, drought in the Southwest has seriously depleted water resources
of many towns and cities, especially in Arizona. Tucson was formerly the largest
municipality in the country sustained by groundwater. However, after years of
overpumping and less-than-average precipitation, the aquifer has been
significantly reduced.
In response, the
city has developed and adopted a Water Harvesting Guidance Manual, a tool to
help guide residential and commercial developers plan strategies for
implementing water harvesting for new developments, including city
projects.
“The Water
Harvesting Guidance Manual incorporates a long-term view on water
sustainability,” says Ann Audrey, environmental projects coordinator for
Tucson’s Office of Conservation and Sustainable Development and the manual’s
editor. “It is based on the need to reduce our dependence on groundwater, which
has been seriously depleted, and on Central Arizona Project water, which is very
expensive.”
The primary goals of
the manual and Tucson’s water-harvesting program are to reduce water demand,
extend water reserves, and best use the opportunities of rainwater. Water
harvesting and stormwater retention designs outlined in the manual include
microbasins, on-contour and off-contour swales, French drains, gabions, water
tanks and cisterns, and the use of mulch. In addition to harvesting water, the
designs aim to improve stormwater discharge quality, while at the same time
decreasing discharge quantity. The water-harvesting program complements the
city’s Xeriscape requirements in the Land Use Code, another external
water-use-reduction program that encourages the use of native, drought-tolerant
landscaping. Cumulatively, these practices are designed to create a sustainable
water model for Tucson and preserve the city’s groundwater supply for the
future.
“The basic philosophy in the Southwest for years in
terms of stormwater management has been to treat runoff as a waste instead of a
resource,” says Frank Sousa, lead hydrologist with Tucson’s Office of
Conservation and Sustainable Development. “We’re trying to change that paradigm.
Stormwater should absolutely be viewed as something to use and benefit
from.”
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Photo: Ann
Audrey |
| Large basin collecting runoff water from a parking lot in Sierra Vista, AZ |
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Photo: Ann Audrey |
| Microbasin capturing rooftop runoff in
Tucson |
On average, Tucson
receives approximately 11 inches of rain per year. However, rainfall events can
be complicated. “In the winter, rainfall in our region is gentle and
semi-reliable,” says Sousa. “But our summers are characterized by intensive,
localized, and conductive thunderstorms. It’s not unusual during these times to
receive an inch and a half of rainfall in 30 minutes. As such, with very
infrequent and non-uniform rain supply, it is very important to find ways to
slow down runoff, increase retention, and facilitate more uniform groundwater
recharge.”
Presently, about 40%
of Tucson’s potable water usage is allocated toward landscaping. Taking into
account the region’s water scarcity, Audrey says that this usage is a big draw
on a limited resource. “The water harvesting program aims to reduce that
external water usage. Stormwater that is collected or captured is utilized to
supplement irrigation systems for commercial developments,” she
says.
The Water
Harvesting Guidance Manual outlines a process for evaluating site conditions and
developing integrated designs that match the characteristics of the
landscape. An efficient design is
described as saving resources, while improving the function and sustainability
of the site. Effective water harvesting systems reduce water consumption, energy
requirements, and landscape maintenance, and are site-adaptive for various
developments such as subdivisions, commercial sites, public buildings, and
public rights of way. Tucson’s manual was created as a general guide;
implementation of specific water harvesting techniques requires site-specific
modification, sizing, and engineering.
“There is basically
an unlimited amount of different water-harvesting methods with a huge range of
associated costs,” says Sousa. “Each site is unique, so it’s very important to
find and implement a customized system that is adaptive to the specific onsite
conditions. It needs to work with the contours, drainage, and landscape.
Cookie-cutter designs can be functional, but they won’t achieve maximum
efficiency.”
The manual describes
the use of microbasins, which can be effective on gently sloping or nearly flat
land areas with low volumes of runoff water. They can also be designed in a
series for areas with more concentrated runoff, with offset spillways to create
longer flow paths that facilitate more soil infiltration. Microbasins can also
be constructed on contour to intercept water running off a ridge, or as
localized depressions or lowered soils levels inside curbed areas for rainwater
retention.
On-contour swales
are described as water-harvesting techniques in small- to moderate-sized
watersheds with moderate volumes of shallow, slow-moving stormwater such as open
space areas and parks. One example is a large-scale parallel on-contour swale,
which is discussed as a retention/detention feature. In the design, a first
swale intercepts water and retains it for use. The second swale, in turn,
intercepts overflow stormwater from the first swale and can convey excess
stormwater offsite, if necessary.
Off-contour swales
are recommended for design in moderate-sized watersheds at a slight angle from
the contour line and function to convey stormwater slowly downslope in a
controlled manner to maximize infiltration, support vegetation, control erosion,
reduce stormwater flow velocity, and eventually discharge any excess stormwater
in safe locations. Off-contour swale types include pocket swales where a water
bar, or gently sloping berm, is installed across a travel surface, extending
beyond, and then hooking back to the travel surface, creating an adjacent
depression for intercepted stormwater to collect. Other off-contour swale
designs include boomerang swales and parking lot berms.
On flat to moderate
slopes, French drains are detailed in the manual as effective techniques for
intercepting low to moderate-sized flows and encouraging rapid stormwater
infiltration through the sides, ends, and bottom of rock-filled trenches. French
drains are appropriate for along pathways, for intercepting rooftop runoff, and
in vertical gravel columns, which can direct stormwater into the ground around
tree roots.
The manual describes
the use of gabions in small watercourses, such as narrow and wide streambeds,
which function as semi-permeable barriers or grade control structures to slow,
but not stop, the flow of stormwater. Gabions also prevent or repair upstream
erosion, trap rich detritus, and allow stormwater to infiltrate into the channel
sediments and adjacent soils.
Water tanks can be
used for collecting and storing rooftop runoff for use at a later time, while
mulch is an effective technique for reducing evaporation from soils. Indeed, in
comparison to Tucson’s 11 inches of annual rainfall, evaporation of standing
water averages around 78 inches per year as solar energy quickly evaporates soil
water brought to the surface by capillary rise. Mulch placed over bare soils in
water-harvesting depressions can reduce temperatures and thus limit moisture
loss from soil. In October 2008, the Tucson City Council passed an ordinance
requiring new commercial developments to harvest rainwater for landscaping. The
rule, which goes into effect in 2010, says that 50% of water used for
landscaping must come from captured rainwater. Tucson is the first city in the
US to pass such an ordinance.
New Mexico
In neighboring New
Mexico, similar water-harvesting initiatives are being considered, planned, and
implemented on various levels. One of the newly instated missions of the city of
Santa Fe is to promote the use of stormwater as a clean, valuable, and
sustainable natural resource. Traditionally, the city has encouraged active and
passive rainwater-harvesting techniques through the city’s terrain management,
storm drainage, and landscape ordinances. Developers who implement such
strategies can get credits applied for open space
requirements.
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Credit: City of Santa Fe |
| At the Santa Fe Railyard Park and Plaza, rainwater from building roofs is stored in underground cisterns and a 35,000-gallon water tower and used for landscape irrigation. |
Jim Salazar,
division director for the Santa Fe Storm Water Management Division, says that
although the city does not yet require water harvesting, there are bills in the
works that are being developed to adopt these practices. The measures are being
implemented as a response to drought conditions that have affected Santa Fe for
a number of years.
“New residential
green building codes are slated for adoption that will allow points to be gained
towards building permit issuance by using rainwater-harvesting and -infiltration
techniques. Additionally, new drainage and stormwater ordinances requiring
passive and active rainwater-harvesting techniques for new land developments are
being written,” he says. “Typically, stormwater measures have been for the
purpose of drainage control, but now they are very important in terms of
promoting water conservation.”
Salazar says that
although it is not yet required in the city’s codes, the city is asking and
encouraging developers to use every opportunity possible for implementing
rainwater harvesting and stormwater retention in a beneficial way, mainly for
diverting to landscape areas for irrigation purposes.
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Photo: City of Santa Fe |
| Underground cisterns at the Railyard Park and Plaza |
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Photo: City of Santa Fe |
| A cistern at a new Santa Fe city library |
Passive techniques
being implemented by the city, where rainwater is diverted without the use of
mechanical systems, include rain barrels placed below a roof drain, curb cuts,
and depressed landscape medians. Active techniques include rainwater and
stormwater collection systems with a pumping component for landscape
irrigation.
Over the last couple
of years, several new Santa Fe projects have incorporated rainwater-harvesting
methods. Santa Fe’s new Civic Center, which has a roof surface area of 75,000
square feet, includes a catchment system and roof rainwater cisterns capable of
storing 45,000 gallons. Another city project, the 12.5-acre Santa Fe Railyard
Park and Plaza, includes water-harvesting systems that capture rainwater from
nearby building roofs and store it in 75,000-gallon cisterns buried below the
newly built park and in a 35,000-gallon water tower. The rainwater stored in the
cisterns and the water tower will be used for landscape irrigation at the park.
Additionally, the new city library features a rooftop harvesting system and a
26,000-gallon storage tank. “For every new city project, we are looking at ways
to utilize impervious surface and find opportunities to harness stormwater in a
beneficial way,” says Salazar.
Other water
conservation incentives being offered by the city include a rain barrel credit
program. Residents who buy rain barrels receive a one-time $30 credit toward
their water bill. “The city is also promoting low-water-use appliances and
plumbing appurtenances as well as looking into ways that rooftop runoff can be
diverted for flushing toilets,” says Salazar.
Salazar says the
city’s Storm Water Management
Division is also promoting a stormwater infiltration program, which includes the
use of infiltration technologies such as bioretention and low-impact development
(LID) techniques. “We are in the process of changing the way we approach land
development,” says Salazar. “We are heading in a direction that encourages more
use of LID technologies for site design.” This initiative also includes a pilot
program for the use of porous pavement systems. “We are being very proactive and
using every opportunity we can to promote the infiltration of stormwater back
into the ground,” says Salazar. “Our overall philosophy toward stormwater
management is definitely heading in this direction.”
Some of the
different infiltration systems the city is using include bioswales, such as
roadside collection ditches that are used for smaller-scale developments,
bioretention ponds, permeable pavements, rain gardens, and other techniques that
facilitate stormwater infiltration and aquifer recharge.
Santa Fe County
has implemented similar water harvesting measures because of ongoing and
sustained drought. The Santa Fe County Water Conservation Program includes
stormwater and water-harvesting requirements to ensure that residential and
commercial development is sustainable and built in a way to conserve water
resources. “The Water Conservation Program was created as a way to conserve
water that is drawn from our domestic wells,” says Wayne Dalton, permits and
enforcements manager for Santa Fe County.
According to the
guidelines, all residential development is required to collect roof drainage
from a minimum of 85% of roof area for reuse in landscape irrigation. Residences
that have 2,500 square feet of heated area or less must use rain barrels,
cisterns, or other catchment basins. Residences over 2,500 square feet must
install active rainwater catchment systems comprising of cisterns. For
commercial development, all roof drainage is required to collect in cisterns for
reuse in landscape irrigation.
Santa Fe County
land-use regulations also require retention ponds to be used for capturing
stormwater from rooftops and hard surfaces to facilitate onsite ponding and
allow proper drainage. “Generally, a good practice is to have landscaping
located in proximity to the retention ponds,” says Dalton. “However, the best
use of collected rainwater that I have seen for watering landscapes is through
drip irrigation. These systems operate with timers and apply water directly to
the soil where it is needed. They are highly efficient.”
In addition to
the water harvesting requirements, the county has implemented an ordinance
requiring that all new residential and commercial development install
hot-water-recirculation systems, which work to instantly activate hot water.
“Cumulatively, it is estimated that up to 17,000 gallons per year can be saved
with these systems,” says Dalton.
Atlanta,
GA
In Georgia, a
severe and prolonged drought has affected the northern third of the state,
causing severe water shortages. Buford Dam, the primary water supply for metro
Atlanta, has fallen to 38% capacity, and Georgia Governor Sonny Perdue released
an executive order declaring a state of emergency in 85 counties across the
state because of exceptional drought and the subsequent threats to the water
supply in those areas. The executive order stated that numerous lakes and
reservoirs have experienced record-breaking low water levels, putting the
availability of drinking water for over 4 million citizens at great risk.
Georgia residents, businesses, and industries are required to be extremely
vigilant in exercising aggressive water conservation
methods.
“In 2007, the
region’s precipitation levels came very close to 1954 levels—the driest year on
record,” says Sally Mills, deputy commissioner with Atlanta’s Bureau of
Watershed Protection. “In the upper state of Georgia, a level 4 drought stage as
been declared. It is very serious and very severe.”
In addition to
his executive order, Governor Perdue directed the Georgia Environmental
Protection Division to require a 10% reduction in drinking water systems for 61
drought-stricken counties. “These are the highest levels of water restrictions,
which include a broad prohibition of water usage,” says Mills. “The state is
working with industries, providing audits, initiating public education,
conducting inspections, and issuing fines for uses that violates the
restrictions.”
At the local
level, a residential initiative has been implemented involving a policy on water
reuse. Citizens are being encouraged to use less water and also to install
cisterns or catch basins—anything that can be bought from a retail store like
Home Depot and used to retain or capture water. Such measures extend as far as
taking buckets into the shower and using excess water as landscape irrigation.
Atlanta is also considering more use of Xeriscape and landscaping that
incorporates more native plants and drought-tolerant
species.
However, Mills
says that although water retention strategies are possible in small individual
kinds of ways, the city is not initiating any large-scale municipal stormwater
collection or redistribution policies, because, practically speaking, the region
is in such a drought that stormwater retention is not feasible. “There is
literally no accumulation or ponding,” says Mills. “From a surface water
management perspective, we have no stormwater delivery
options.”
Additionally, the
district’s overall watershed plan does not necessarily include reuse. “The city
of Atlanta does not have large expanses of landscaped areas that could benefit
from supplemental irrigation, which would be one of the most practical uses of
retained stormwater,” says Mills. “The existing policies are centered on
returning flows to the region’s rivers and tributaries, which is consistent with
the district’s strategy for managing the basin. In this way, the flows can be
better quantified in a hydrologic model.”
Another drawback
is that a major reuse system would require a large capital investment and the
building of parallel infrastructure. “The construction of this secondary system
could have adverse impacts on neighboring streams and tributaries,” says
Mills.
Looking ahead,
Mills sees every indicator pointing toward continued dryness and unusually warm
conditions. The governor has also created a Drought Response Unified Command and
a Drought Response Working Group, which are coordinating more objectives and
strategies for better responding to the drought emergency.
Forgotten
Rain
One Phoenix,
AZ–based company is advocating rainwater harvesting by acting as a consultant to
large-scale property owners and developers, advising on various techniques and
strategies for obtaining certification from the US Green Building Council’s
Leadership in Energy and Environmental Design (LEED) rating system. Forgotten
Rain LLC is a company dedicated to rainwater harvesting, stormwater reuse, and
rain garden design for private and city projects.
“By incorporating
sustainable designs and meeting LEED guideline requirements, property owners and
developers can obtain benefits such as tax breaks and other financial
incentives,” says Heather Kinkade-Levario, president of Forgotten Rain. “In
addition to those incentives, property owners who implement rainwater harvesting
and other techniques can have self-sufficient systems and full control over
water quality and supply.”
Kinkade-Levario
says her efforts in consulting are a different and more effective approach than
the direction she was previously taking with her company. “I used to spend a
considerable amount of my time promoting stormwater retention and rainwater
harvesting to cities, helping them become more aware and understand how to
implement various techniques,” she says. “However, I found governments were too
slow to react. I wasn’t seeing the type of results I had envisioned. Now that I
have taken a corporate direction and a top-down approach working directly with
property owners, I’m seeing much more progress. As an advocate, this is a much
better way to push my goals.”
Kinkade-Levario
has served as president of the American Rainwater Catchment System Association
(ARCSA), where she led an effort to instate an accreditation for rainwater
professionals. Currently, ARCSA is advocating for legislation that would
standardize different types of systems, in addition to developing rainwater
harvesting and stormwater reuse goals for cities to adopt. “Most county and city
development guidelines include codes for plumbing, roofing, and gutter systems,
but not necessarily for rainwater harvesting,” she says. “Engineers and
architects also need to become more updated on implanting these techniques into
development plans and designs.”
As the severity
of drought and water supply escalates, Kinkade-Levario is finding that more
cities and municipalities are recognizing the importance of rainwater harvesting
for reuse. “Tucson, for instance, has really embraced a number of strategies
because of their water scarcity situation,” she says. “However, in Phoenix, the
level of commitment is much less. Phoenix currently has more water supply
options, such as a canal that conveys Colorado River water and dams that collect
rainwater. They are not nearly as progressive as Tucson because they perceive
their situation as less dire. They are starting to consider rainwater
harvesting, but nothing is being required at this point.”
With urban sprawl
and horizontal development characterizing growth in Phoenix, a considerable
amount of opportunities exist for implementing rainwater-harvesting systems.
Large-scale slabs of impervious surfaces, such as car dealerships that can take
up as much as 800,000 square feet, are ideal areas for installation of catchment
systems. “There is no reason why, especially in drought-prone regions, these
spaces shouldn’t be utilized to catch and retain rainwater and stormwater,” says
Kinkade-Levario. Because rain events in the Southwest can be sudden and
intensive, harvesting systems should be planned with capacity in mind. “A sudden
burst of 1-inch of rainwater over 100,000 square feet is a considerable amount
of water volume,” says Kinkade-Levario. “These rain events only come twice a
year in our area, so it is critical that rainwater and stormwater retention
systems are able to convey flood-like waters by including large storage
areas.”
Kinkade-Levario
says there are many more strategies and accessible techniques for harvesting
water. “Cooling towers are a great example of an alternative water source,” she
notes. “These units contain lots of available water for reuse that is otherwise
just going into the sewer. Two buildings in Phoenix and one in Kingman, AZ, are
currently utilizing cooling blowdown water to irrigate their total site.
Anything that is not blackwater should be reused.”