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Summer 2011

Urban Jungle

The changing natural world at our doorsteps | Illustration and text by Patterson Clark      

The National Mall's turf panels.

Some turf panels are long, some are short.

June 28, 2011

Upgrading the lawn at the National Mall

The Smithsonian Folklife Festival will soon
blossom on the Mall, drawing 2 million feet that will trample the turf and pack down the soil, which is already so dense and compacted that it's almost as hard and impermeable as concrete.

Dredged from the Potomac River in 1882, the silt-
and-sand soil is a poor mix for a lawn that must recover from constant foot traffic and extended shade from temporary tents.

The grass gets little help from the Mall's irrigation system, which has been damaged by trucks driving across the surface and tent stakes puncturing the pipes. As a result, the National Park Service must manually irrigate the exhausted turf.

But greener days are on the horizon for the Mall's turf panels, the open, grassy fields at the eastern end of the Mall. In September, contractors are scheduled to begin renovating the panels, beginning with eight of them between 3rd and 7th streets. That phase of the project should be complete by October 2012.

The top six to 18 inches of soil will be enhanced with a mixture of coarse sand and compost, which will alleviate compaction and increase water permeability.

Panels will be raised 2 inches higher than

surrounding walkways and each panel will be edged by a granite curb-and-gutter system to channel rainfall runoff into underground concrete cisterns, which will supply water for a new, more durable irrigation system.

Although the turf will still host high-impact events, the grass will recover quicker than before.

A cross section though the edge of an upgraded turf panel.

SOURCE: National Park Service