Research Design Connections
Researchers study woodpeckers, "safe routes to school," sidewalk surfaces, and rain gardens.
By Jean Marie Cackowski-Campbell, ASLA, and Sally Augustin
Landscape Architecture, in partnership with the web-based newsletter Research Design Connections, will continue to
use this column (the previous example appeared in the February 2006 issue) to report current research of interest to landscape architects
from a wide array of other fields.
We welcome your comments, suggestions about future topics, and studies you have encountered in your own practice.
Rain Gardens Don’t Cleanse Polluted Water
In a pioneering study of the ability of rain gardens to treat stormwater for pollutants and to reduce runoff, Michael Dietz and John Clausen
determined that the rain gardens they constructed “worked well for overall flow retention, but had little impact on pollutant concentrations”
in the water draining through the garden.
The researchers defined rain gardens as “shallow depressions in the landscape that are planted with trees and/or shrubs, and covered
with a bark mulch layer or ground cover. They allow stormwater to infiltrate, recharge aquifers, and reduce peak flows. In addition,
they are expected to provide pollutant treatment, which has been attributed to several processes including absorption, decomposition,
ion exchange, and volatization.”
Two test gardens were constructed in Haddam, Connecticut. They were designed at a size to store the first 2.54 centimeters (1 inch)
of runoff from an asphalt-shingled roof that was 106.8 square meters in area. The surface dimensions of the rain gardens were 2.74 meters
by 3.35 meters. In the test garden the researchers set out to measure the volume and composition of water entering the garden, or influent;
the overflow, or effluent; and water percolating through the soil, or percolate flow. They measured these flows using tipping buckets,
and also measured the amount and composition of rainfall. Water samples taken throughout the system (from inflow to outflow) were
analyzed to assess levels of the following substances: total phosphorus, total Kjeldahl nitrogen, ammonia–nitrogen, and nitrite+nitrate–nitrogen.
All of these substances were poorly filtered from the roof runoff. Only ammonia– nitrogen was significantly lower in the garden effluent
than in the influent in both gardens, although in one garden the total nitrogen (total Kjeldahl nitrogen concentrations plus ammonia–nitrogen
concentrations) was lower in the effluent than the influent.
The gardens proved more effective at capturing water. Less than 1 percent of the water inflow into the garden overflowed, indicating
that the rain garden “reduced the peak flow rate and increased the lag time of influent water.”
“Installing a rain garden without an underdrain may not be appropriate in all situations,” the authors conclude. “However, given the high
overall retention of flow found for the 2.54-centimeter design method used in this study, a rain garden could be an effective bmp [best
management practice] in reducing flow and pollutant loads if an underdrain were not connected to the stormwater system.”
- “A Field Evaluation of Rain Garden Flow and Pollutant Treatment,” by Michael Dietz and John Clausen; Water, Air, and Soil Pollution,
vol. 167, 2005.
“Safe Routes to School” Projects Increase Pupil Physical Activity
Providing students with safe walking and bicycling routes to school seems to increase the exercise they receive on the way there, say
Marlon Boarnet, Craig Anderson, Kristen Day, Tracy McMillan, and Mariela Alfonzo, authors of a study of the California Safe Routes
to School programs. This is important because, as reported in the 2001 National Household Travel Survey, fewer than 16 percent of
students aged 5 to 15 walk or bicycle to school now, compared to 48 percent of students three decades ago.
Safe Routes to Schools programs can involve education, traffic-law enforcement, or engineering changes on the routes students may take
to school. This project by Boarnet et al. focused on how changes in the built environment affected active travel to school.
The construction projects at the participating schools were described as either sidewalk improvements (constructing new sidewalks, filling
gaps in the sidewalk network, building walking paths, and installing curbs and curb cuts), crossing improvements (adding crosswalks,
installing in-pavement crosswalk lighting, and installing a pedestrian-activated
signal that warns pedestrians of the amount of time remaining to cross the street), or traffic control (installing a traffic signal).
Sidewalk improvements and traffic control seemed to have the greatest impact on the frequency with which children walked or rode their
bicycles to school.
Children who encounter California Safe Routes to Schools engineering projects on their way to school seem to walk or ride their bicycles
to school more frequently than children who do not have access to such projects. Of children who pass through these projects, 15 percent
increased their walking or bicycling to school after the engineering improvements, while only 4 percent of children who did not encounter
such projects increased their frequency of the same sorts of travel.
Parents of third- to fifth-grade students in 10 demographically diverse schools near California Safe Routes to Schools participated
in this study. Budget constraints and a tight schedule forced researchers to use a single questionnaire to collect data from parents about
how children near Safe Routes to School projects were traveling to school. The questionnaires were administered one to 18 months
after the completion of construction. At most schools, the survey was administered within a year of construction being finished. Whether
parents noticed the construction project or had a favorable opinion of it did not seem to influence their reports of the frequency with
which their children walked or rode their bicycles to school. The researchers did not measure the total physical activity by students,
nor did they collect information about the distance between students’ homes and schools.
Nonetheless, the authors feel that their results are meaningful because the impact of the Safe Routes to School engineering projects
was probably not influenced by any other physical features in the area. In addition, both the children who did and did not encounter
projects on the way to school would have experienced the same, if any, general changes in the environment (such as climatic changes),
school-sponsored education programs, and societal factors that might have resulted in changes in walking or bicycling frequency.
This research confirms the outcomes of earlier studies and is itself a groundbreaking effort to study the effect of Safe Routes to Schools
construction projects near schools with varied demographics, built-environment settings, and varied engineering improvements.
The authors conclude, “The research presented here suggests that small but strategic pedestrian or bicycle facility improvements
may impact the propensity of children to walk or bicycle to school. Improvements to sidewalks and traffic control systems look especially
“Evaluation of the California Safe Routes to School Legislation: Urban Form Changes and Children’s Active Transportation to School,”
by Marlon Boarnet, Craig Anderson, Kristen Day, Tracy McMillan, and Mariela Alfonzo; American Journal of Preventive Medicine,
vol. 28, no. 2, supplement 2, 2005.
“Active commuting to school an overlooked source of children’s physical activity?” by C. Tudor-Locke, B. E. Ainsworth, and
B. M. Popkin; Sports Medicine, vol. 31, 2001.
Optimal Surfaces for Wheelchair Travelers
Standards from the International Standards Organization indicate that people in wheelchairs can be adversely affected by vertical
vibrations affecting their whole bodies as they travel over various surfaces. The negative effects include low-back pain and disc
degeneration. A recent study investigated which generally available surfaces minimize these vibrations. The study was partially funded
by brick and concrete pavement industry trade groups including the Interlocking Concrete Pavement Institute (ICPI), federal agencies,
and national nonprofit organizations.
The researchers used a poured-concrete surface as a control. In addition they made six test sidewalk surfaces from interlocking
concrete pavement and two from clay brick; all were installed to industry standards. Other variables included chamfer widths
and the angle of bricks and pavers in a herringbone pattern, a common pattern used in sidewalks and other public paths.
To measure the vertical vibration over the test surfaces, the
authors first calculated the root-mean squares of vibrations in
each direction (vertical, fore-aft, and side to side). For each
surface, they used average root-mean square values in the vertical
direction as the metric of comparison.
In both manual and powered wheelchairs, and also at both the
1-meter-per-second and 2-meter-per-second speeds at which powered
wheelchairs traveled over these surfaces, test conditions for
two surfaces consistently produced the lowest levels of vertical
vibration: concrete, 0-millimeter chamfer width, 90-degree herringbone
angle; and concrete, 2-millimeter chamfer width, 90-degree herringbone
For both manual and powered wheelchairs traveling at either 1
or 2 meters per second, the levels of vibration on these surfaces
were lower than the poured-concrete control sidewalk. For the
manual chairs the difference between the control surface and the
surface of concrete, 0-millimeter, 90-degree angle was significant.
At a speed of 2 meters per second, vibrations from traveling on
both surfaces were significantly lower than those from the control
sidewalk. In both cases, the concrete surfaces were made of ICPI
After testing the vibrations experienced by people traveling
in manual and powered wheelchairs over these surfaces, the authors
concluded that using selected ICPI pavers “would be acceptable
for any route traveled by individuals using wheelchairs.” The
authors go on to state that a “90-degree herringbone pattern is
preferred over the 45-degree patterns.” For safety reasons, a
bevel of less than 6 millimeters should be used.
“Vibration Exposure of Individuals Using Wheelchairs Over
Sidewalk Surfaces,” by Erik Wolf, Jonathan Pearlman, Rory Cooper,
Shirley Fitzgerald, Annmarie Kelleher, Diane Collins, Michael
Bonninger, and Rosemarie Cooper; Disability and Rehabilitation,
vol. 27, no. 23, 2005.
Using Woodpeckers as Biodiversity Markers
Woodpeckers are useful for more things than keeping you from
drifting off to sleep on a long midsummer afternoon. The concentration
of woodpeckers in urban parks signals the strength of other bird
and mammal communities that are dependent on cavities and deadwood
for food and shelter. They broadcast the biodiversity of an area.
Biologists Joan Morrison and William Chapman investigated the
number of woodpeckers of various species in six urban parks in
Hartford, Connecticut, and found that more than 90 percent of
the variation in woodpecker concentrations in the parks they studied
could be attributed to a combination of “park area, basal area,
and the number of trees that were [greater than or equal to] 50
percent dead.” The biologists determined the number of trees that
were at least 50 percent dead visually, using the number of obvious
dead trunks and branches. They estimated the basal area (the cross-sectional
area of the stems of plants in a stand) using random sampling,
and employed gis software (ArcView v. 3.2a) to estimate the total
park area. The researchers determined that “the number of woodpecker
species present in each park was correlated with total park area
but not total wooded area, suggesting that some patches of wooded
area in parks may be too small to support some species.”
All of the parks in this study had wooded sections; others also
had scrubland areas and open, grassy fields that are mowed regularly.
A few also contained ornamental gardens, golf courses, picnic
areas, or ball fields. All are regularly visited by people. Heavily
urbanized areas, including roads, surround each park. Woodpecker
populations in these areas were compared to those in a more rural
area at the Trinity College Field Station in Church Farm, Connecticut,
which is contiguous and contains a temperate deciduous forest.
Populations of woodpeckers were counted in both areas in June,
July, and August 2001 and 2002, and in June and July 2003.
“Although our study was limited to only a few parks in one city,
the results suggest that urban parks, particularly those with
large areas of wooded habitat, can contain habitat suitable for
primary cavity nesters,” the authors conclude, adding, “Even small
areas such as urban parks can have some value for regional conservation
of biodiversity. Recommendations for enhancing the value of urban
parks for woodpeckers and other species dependent upon dead and
dying trees include identifying park areas where these resources
can be maintained, yet where the safety of park visitors is not
compromised [by dead branches falling].”
“Can Urban Parks Provide Habitat for Woodpeckers?” by Joan
Morrison and William Chapman; Northeastern Naturalist,
vol. 12, no. 3, 2005.
Jean Marie Cackowski-Campbell, ASLA, is the publisher
of RDC and has an mla degree from Ohio State University. Sally
Augustin, RDC’s senior editor, is an environmental psychologist.
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