Interview with Jeff Hutchin, Mia Lehrer + Associates
By Leslie McGuire, managing editor

During a regular rain event, the permeable concrete paving itself takes out the larger materials. The base underneath will take out even more and the sand below that will give it additional filtration. When it gets to the water table it has been cleaned up.
Images courtesy of Mia Lehrer + Associates

Landscape architecture firm Mia Lehrer + Associates with the Santa Monica Mountains Conservancy and Mountains Recreation and Conservation Authority, officially opened Vista Hermosa, a nine and a half-acre park located in downtown Los Angeles.

The park, which just opened on 7/19/08, layers in sustainability practices, including storm water collection in a subsurface cistern for on-site irrigation use, meadows and bioswales that filter the water before it enters the cistern, plus permeable materials used in the parking lot and pathways.

To keep every drop of water that falls on site, all of the park?EUR??,,????'???s ground surfaces are made from permeable materials that allow water to seep through to irrigate plants. A 20,000-gallon underground cistern captures and circulates water throughout the park. The sustainably designed park is an urban watershed demonstration project that accommodates community and school recreational programs, integrated with an extensive network of introduced natural features and ecosystems. Located at the edge of a dense residential zone, bounded by First and Colton, Beaudry and Toluca streets, the park incorporates active recreation including a synthetic turf soccer field, with trails, water features, a children?EUR??,,????'???s adventure area and picnic areas in native habitat landscapes.

 

Individual Parking Stalls
ABOVE & BELOW: The pervious concrete is twice the thickness for the parking lot aisles, as there is some heavy truck/bus traffic related to goods delivery/trash pick-up, etc.

Parking Lot

Although permeable paving is in the parking lot, it is not directly attached to the cistern. The cistern collects water from the entire site. The extensive meadow has area drains that are connected directly to the system. Area drains are on the top shelf of the play area as well as over by the grotto and the fountain.

There is a drain in the parking lot for overflow if the capacity of the area is filled. That overflow goes to the street drains or the cistern. They?EUR??,,????'???re not simply collecting the water and sending it to the cistern, they?EUR??,,????'???re also letting it go back down to the water table after it gets filtered through the soil and base materials.

This was the mega-school/housing/retail complex that the Los Angeles Unified School District began building more than a decade ago. It was a real problem almost from the groundbreaking, as the LAUSD was clearly out of its element. Then, construction on the site at First and Beaudry streets was halted due to the discovery of dangerous underground gases. The subsequent finding of an earthquake fault killed progress on the half-built campus, even though hundreds of millions of dollars had been spent. Ultimately the decision was made to tear down two existing buildings and divide the property, creating the school on one side and the park on the other. Steps were taken to build away from the earthquake fault and mitigate the danger posed by the gases.

There perimeter walkway is made of permeable decomposed compacted granite. Also, permeable concrete pavers are on the site around the office building. They are spaced half an inch apart for added permeability.

There used to be oil fields on the site, so methane gas mitigation was required. The mitigation measures helped with the permeability because of the sand layer. The theory behind the system is that if there?EUR??,,????'???s a crack in the earth and a concentrated area of gas was coming up, it would hit the sand and then after percolation go on up at safe non-flammable levels. Three feet of the soil had to be excavated and then filled back in with compacted sand. Then another 18 inches of soil was added on top of that. Another advantage of the permeable concrete, which looks like rice krispies and is colored ?EUR??,,????'??kahlua,?EUR??,,????'?? is that one isn?EUR??,,????'???t able to see the patch work that well in case of cracking.

There are only a few contractors who are registered to pour and finish this type of paving. These contractors must be certified because it takes a special tool?EUR??,,????'??+a rolling screed?EUR??,,????'??+and it is dry mixed. If it gets over worked, all the holes dry up and the paving loses its permeability.

The cisterns capture the water to use for irrigation. The cistern is attached to a pump that gets turned on when it?EUR??,,????'???s time for use with the drip irrigation. If the cistern is dry, there?EUR??,,????'???s a float switch in the cistern that will automatically turn it over to the main irrigation line. Even during construction it rained a bit and the cistern worked very well collecting.

The individual parking stalls are 6-inch thick permeable concrete. Under that is a 12-inch soil buffer and under that is 18 inches of sand. The base material is a regular road base of crushed rock, which has to be extra thick because of the mitigation measures that had to be put in place.

An adjacent soccer field will be shared by the LAUSD and the city Department of Recreation and Parks. From the field?EUR??,,????'???s artificial turf to the mostly native Southern California plants, everything is designed to be eco-friendly.

Synthetic turf was used in the soccer field and the entire field drains into the cisterns. Quick-Couplers are out there so LA Unified can wash down the field. That water is also collected and re-used. The system saves water and is also cleansing and recharging the water table. Any water that falls on the site stays on the site which keeps all the water from going into the storm drains and then into the ocean.

Nine and one-half acres are involved in the water collection. The 20 thousand gallon cistern and the meadow have the capacity to hold 100 thousand gallons of water. During a rainstorm while under construction, the cistern was full and holding all the water very well.

The picnic areas are also decomposed granite. The only hard paving is in the parking lot. There are some handicap ramps that are solid nonpermeable concrete as well. Those ramps have curbs on either side, but the curbs are slotted so water can run off quickly and go back into the ground rather than concentrating at the bottom of the ramps.

Nearby residents of Westlake, Angelino Heights, Chinatown, Central City, Little Tokyo, and downtown Los Angeles, now have unique access to both athletic facilities and a chance to experience nature within walking distance of their urban neighborhood. Vista Hermosa is intended to be more than a recreational park, however; it is envisioned as an educational platform from which children develop knowledge, and are inspired to have pride in their community.