Watershed are urban features
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| Watersheds in Baltimore |
Watersheds are important parts of both wild and civilized places. In both city and countryside, watersheds express
the flow of water, with its power to connect places, its ability to accumulate
and move chemicals and materials, its capacity to support rich biological
activity, and its power to nourish human life.
Watersheds are a fundamental part of all ecosystems and habitats.
What do watersheds do?
Watersheds are areas that collect water by surface flow and in
streams, and accumulate it to the lowest spot within their boundaries. In moist climates, that spot will be a lake,
wetland, or outlet to a larger stream.
Urbanization alters the structure of watersheds in cities and suburbs, speeding
up the rate of water flow and often depressing the biological, physical, and
chemical quality of water. Because those
functions of watersheds are important for the natural world, for the benefits
that people draw from nature, and for people's health, safety, and quality of
life, watersheds in cities are an important, but often ignored or invisible
feature of our constructed habitat.
Urban watersheds are mostly invisible now
Because streams have often been buried in pipes, encased in hard
channels by steep stone or concrete walls, or hidden under streets and
buildings, streams may be virtually invisible in cities and suburbs. Small streams may have been buried or
rerouted due to reshaping slopes, constructing buildings, or laying out
roads. Even some larger streams may have
become "lost," obscured behind factories or on the neglected fringes
of parking lots, or hidden in tunnels and culverts. Without the everyday evidence of streams, city
dwellers and suburbanites may be unaware of the watersheds where they live,
work, and play. This means that they
also do not know about the benefits and risks associated with the flows of
water in their cities and suburbs.
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| Baltimore City streams in 1943 (left) and 1999 (right) |
Urban watersheds are constantly modified
Even though most people may not know about their urban
watersheds, the ongoing construction and reshaping of cities and suburban areas
modifies urban watersheds. It is
important to be aware of how urban watersheds have been modified over time by
urban growth and change. Historical
maps, photographs, and drawings expose the invisible watersheds of our urban
areas.
Many of the alterations to urban watersheds have disconnected
the natural flows of water, or have impaired the biological cleaning functions of
streams and their floodplains. The hard
walls of stone or concrete-lined channels disconnect the streamside soil from
the moisture required to reduce pollution.
The large flows of stormwater from paved surfaces and roofs erodes urban
streams deep into their floodplains, stranding the floodplains high above the
watertable and dries them out. These
changes compromise the ability of watersheds to support plants and animals,
reduce their ability to store organic matter in the soil, and impair the
ability to reduce excessive levels of some urban stream pollutants. The awareness that urban and suburban
watersheds experience disconnections between upstream and downstream areas, and
disconnections between the streams and their banks, is key to improving the
health of those watersheds and restoring the benefits they can provide to
people.
Regaining awareness of urban watersheds
Urban residents and those who design and manage cities and
suburbs can benefit from increased awareness of watersheds in urban areas. Awareness of urban watersheds can come from
personal experience, maps of streams and the pipe networks that deliver fresh
water and remove storm and waste water, depictions of the different aspects of
watershed structure, and visualizations of the beneficial and hazardous flows
in watersheds. It takes effort to
overcome the invisibility of urban watersheds.
Once people become aware of watersheds as a part of their
local sense of place, or through the need to manage and improve watershed and
stream function, knowledge becomes a crucial tool. Knowledge requires data. Careful observations along a whole stream
length, well documented notes of stream and watershed status, repeated
photographs at set locations, and scientific measurements are all examples of
knowledge following from awareness. In
particular, measures of the amount of water flowing in a watershed, its
biological and chemical quality, and the health of organisms that inhabit or
use the streams are important contributions to knowledge about watersheds.
What does knowledge contribute to urban watersheds?
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| Nitrate pollution over time in Gwynns Falls, Baltimore |
The knowledge about streams must extend through time because
of ever changing conditions. It is
necessary to repeat the measures so that the impact of things like drought versus
wet periods, or changes in land use in the watershed, or changes in water management,
can be documented. Of course, this kind
of knowledge, when made available and understandable to residents and managers,
becomes a stimulus for wider and deeper awareness: How is my watershed
doing? Is it changing? How does it compare with other watersheds in
other cities, or outside of town? Sharing
knowledge in understandable terms is crucial to achieving awareness and
supporting community action. Knowledge
helps people to "see" urban watersheds again, appreciate the
connections within them, and helps understand how they change. Knowledge promotes new levels of awareness.
How can urban watersheds be reconnected?
With the combination of awareness and knowledge, people can appreciate
the potential for improving the connections in urban watersheds, and the
ability of those streams and watersheds to do free, useful work for managing
urban water and its benefits to environment and people. Awareness can be a tool for improving sense
of place, not only along streams but also throughout entire watersheds.
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| Connecting neighborhoods with the Gwynns Falls. |
Biologically and socially significant actions may include
the establishment of new flows to compensate for some of the disconnections
city and suburban watersheds have suffered.
Such reconnection can be achieved by softening the stream margins in
cities and suburbs, by reconnecting communities with their watersheds and
streams, and by making social flows -- benefits, use, and enjoyment of urban
streams and streamside habitats -- more obvious and available to neighborhoods
that may not now have access or social investment in their watershed.
In addition to re-connection in urban watersheds, it is
important to slow the normal flow of water throughout urban areas.
Increasing infiltration of water, constructing structures upstream that
absorb and retain water, and reducing the amount of water used in wasteful
irrigation practices are examples of slowing water flow through urban
watersheds. Attention to roofs, house
gutters, rain barrels, rain gardens, green roofs and other upstream
interventions can contribute to slowing the flows in urban watersheds.
Recognizing that our cities and suburbs still contain watersheds
and that these watersheds present many benefits and opportunities for
connectivity and controlling water flow, is an important tool for design,
planning, management, and social revitalization.
Box 1: Some Practical Actions for Learning About Urban Watersheds
- Map streams, pipes, and boundaries of urban watersheds.
- Map loss of original streams.
- Conduct tours along watershed length.
- Collect data on water flow and quality.
- Interpret and share watershed data with residents and decision makers.
- Focus on new designs and retrofits that slow the flow of water in urban watersheds.
- Engage residents in re-envisioning their watersheds.
- Assemble "then and now" photos and drawings of watersheds and streams.
- Promote science and art interactions focused on watersheds.
- Install are in the watersheds and along streams.
- Produce informational markers about urban watersheds.
- Involve residents in observations of streams and watersheds over seasons and years.
