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Karen Tamir

Rio Piedras Restoration Project

The restoration plan for the Rio Piedras

in San Juan, Puerto Rico establishes a

framework for healthy habitats, an

opportunity to control flooding waters,

and an innovative platform for future

education and research.

Over the past 40 years, the Rio Piedras watershed in San

Juan has been influenced by population growth, develop-

ment, and conversion of farm land into industrial zones.

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T he Rio Piedras is one of five rivers and streams that make up a 6,700hectare watershed within Puerto Ricos greater San Juan Bay Estu-ary, an extraordinary ecosystem of mangrove forests, sea grass beds,coral reefs, mudflats, and brackish water marshes. The river originates in

the headwaters of Marcelo mountain in the area of Lorenzo Marcelo,

known today as Lago las Curias, and flows 12 kilometers to the north

through increasingly dense urban neighborhoods, before spilling into San

Juan Bay Area Estuary and the Atlantic Ocean.

Over the past 40 years a combination of accelerated population

growth, development, and conversion of farm land into industrial zones

has increased sedimentation, contaminant flow, and both the frequency

and severity of flooding. The Rio Piedrass average mean water level is

approximately 1.8 meters, but in 1996 flood waters crested to 6.7 meters,

causing millions of dollars in damage and loss of life.

As part of a comprehensive plan to alleviate flooding, the United States

Army Corps of Engineers (USACE) devised an improvement strategy for

the Rio Piedras and its upstream tributaries. The improvement plan in-

cluded naturalization of a few banks upstream, but it relied heavily on wide

concrete channels to contain the massive amounts of water.

In 2002 Field Operations was hired by the University of Puerto Rico to

create a framework plan for the University Botanical Garden on a 120

hectare site in the heart of San Juan. The site is bisected by a six lane thor-

oughfare and is bounded by neighborhoods on one side and the Rio

Piedras on the other. The portion of the Rio Piedras that abuts the garden

is 2.2 kilometers long, extending from the southwest to the northeast edge

of the garden. Under the USACE plan this stretch of the river was to

become a 12 x 4 meter concrete channel. The framework plan proposed

a new approach for the Rio Piedras that eliminates flooding problems as

mandated by the USACE and turns this hidden, inaccessible stream into a

Field Operations suggested widening the river channel. Soft,

stepping terraces will convey and hold water.The illustra-

tions on page 68 show the organizational diagrams underly-

ing the design framework of the entire Botanical Garden.

BOTANICAL GARDEN AND RIO PIEDRAS RESTORATION PROJECT,

SAN JUAN, PUERTO RICO

Client: University of Puerto Rico Botanical Garden

Design team: Field Operations + Toro Ferrer Arquitectos, Applied Ecological

Services, Marcello Garcia PHD, Gabriel Berriz and Associates, Stan Allen

Architect

Area: 120 hectares (Rio Piedras: 37 hectares)

Costs: 115 million US dollars (Rio Piedras: 45 million US dollars)

Completion: design phase on-going; framework plan phase in March 2006

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public and ecological asset. New spaces, structures, and programs enable

public and academic communities to interact with the river. Programs

proposed along the restored stream include aquatic and agronomic sta-

tions, educational piers, aviary nesting posts, floodplain and wetland plant

exhibits, and recreational upper terraces for picnics, sunbathing, and

playing. Mounds and hollows rise and fall above and below flood levels to

collect water, and create backflow marsh basins. Intermittent islands

increase biodiversity and aviary habitat.

Capitalizing on the Rio Piedrass location and the Botanical Gardens

vast, underutilized land, the river channel will be widened and molded in-

to a series of soft, stepping terraces with varying capacities to convey and

hold water. The new terraces are constructed using ecological restoration

techniques that aid flood control and stabilize the rivers once scoured and

overgrown banks. A 10 x 2 meter low-flow channel will convey the aver-

age daily flow. The first shelf, which is also the primary floodway, provides

conveyance for a typical 2 to 10-year recurrent interval, and a secondary

higher shelf will provide conveyance for a 100-year recurrent interval. The

shelves widths vary depending on available land and specific site con-

straints in each zone. Further, the shelves vary programmatically; with the

first shelf used primarily for research, experimentation and education, the

secondary shelf is intended for recreation and leisure.

A thorough preliminary analysis of six key watershed dynamics

hydrology, hydraulics, sedimentation and erosion, shear stress, velocity

gradients, and vegetation identified surface treatments, bank protection

systems, reinforcement methods, and vegetation regimes that will best

function for each stretch of the stream.

The low flow channel and narrow zones, under bridges and near

existing buildings, require continuous revetment or riprap surface.

Whereas the first floodway shelf is part vegetated and part vegetated

riprap. The secondary shelf, reinforced with erosion control textiles and

Terraces serve as recreation trails connecting the larger San

Juan network of paths and trails with the Rio Piedras. Edu-

cational trails highlight submerged native wetland.

Field Operations studied floodway shelves and bank stabi-

lization techniques in terms of their porosity ratio, capacity

to retain soil, and stability.

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vegetation, is subjected to less frequent stress. A newly added floodplain

in the northern portion of the Botanical Garden is designed to slow the

water down and detain some of the overflow in collection basins, thus

reducing both erosion and peak flow.

To accommodate these variables, Field Operations developed a con-

crete unit that offers flexibility through porosity; each unit has an aper-

ture built into it that can be filled with different materials such as riprap

or plants. Combinations of the unit can make for smooth accessible

ramps, stairs, trails, orderly planting beds, and research plots. Plant

selection for the Rio Piedras corridor was established according to each

speciess adaptability to flash-flood-prone subtropical stream bank envi-

ronments, capacity to maintain channel conveyance, and tolerance to

fluctuating water levels and flow rates. The planting also maintains struc-

tural integrity in soils, habitat qualities, and both educational and aes-

thetic traits. A new arboretum is proposed for the upland slopes, which

over time will become an integral part of the Botanical Garden tree spec-

imen collection.

Owing to its distinctive trajectory through the City of San Juan and the

University of Puerto Rico Botanical Garden, the Rio Piedras is exception-

ally positioned to become a one-of-a-kind urban greenway. Spanning the

distance between the hills to the south and the San Juan Bay Estuary to the

north, the unique public space enables extraordinarily rich tropical ripar-

ian biodiversity and provides a wide range of educational and research op-

portunities. The Rio Piedras is envisaged as a magnet eco corridor for San

Juan, and Puerto Rico as a whole.

The section shows the recreation loop, the Botanical Garden

arboretum collection, upland meadow, trails and the obser-

vation deck in the northern parcel.The historical aqueduct

and educational shed with restored water tanks is located

on the southern reaches of the river.

Various planting regimes were employed for the river banks

and terraces based on each speciess traits.