Practice

Research Design Connections
Researchers study woodpeckers, "safe routes to school," sidewalk surfaces, and rain gardens.

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.

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.”

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 promising.”

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 angle.

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 interlocking pavers.

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.

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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].”

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