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Multi-Purpose Development of the Gila
Drain Floodway
J. Dillon, J.H. Brock, and R.S. Gordon 1
I
The revegetation plan was completed by ASU in May of
1993 and consisted of three sub-tasks: (i) a plant species
recommendation, (ii) a reforestation costlbenefit analysis, and
(iii) a planting and management plan
The vegetation sample from which population estimates were
drawn is classified as a desertscrub community of the Lower
Colorado River Valley subdivi~ion of the Sonoran Desert region
Species recorded conform to a saltbush series with a mesquite
consociation, or "microphyllous desert", increasing westward
along the site. The site itself is an alluvial plain between the
South Mountain range to the north and the Sierra Estrella range
to the south. The Gila River divides the plain' south of the site.
Elevations range from 1040.5 feet to 1115.4 feet, sloping
westward, and average annual rainfall is about 200mm (7.87
inches). Soils are sodic and saline and fall into the alkali
flat/saline loam/saline sandy loam categoty of the general range
index. The soil association is Shontik/Casa GrandelRedun but
closely borders the GunsightlCarrizo/Cristobal association to the
north. Evidence supports the existence of an historic mesquite
bosque on the site and, therefore, the plant species
recommendation is a re-creation of the bosque. This will be, in
other words, a more intensely cultivated version of the existing
native population
A cost/benefit analysis was prepared based upon assumptions
from the planting and management plan The analysis concluded
that future revenues from wood harvested on a sustained-yield
basis from the proposed greenbelt would exceed the marginal
costs of establishment, maintenance and harvesting of the
woodland. The bulk of the funds needed for 10 square miles of
reforestation (estimated at about $13 million over a period of
fourteen years) is expected to come from several federal agencies
and national foundations that have expressed initial enthusiasm
for the project concept. Such funding could partially defray the
costs of floodway construction and maintenance.
Moreover, it is projected that $13 million (current dollars) in
revenues will have been realized, by the 15th year, from the sale
of wood products derived from planned thinning of the
reforested area. Additional revenues are projected from
sustained-yield hatvesting of the more valuable hard wood
beyond the 15th year.
A major "greenbelt" reforestation effort appears feasible
south of Phoenix as part of a mUlti-purpose floodway
development project This project, located within the northern
" Borderlands" portion of the Gila River Indian Community,
would involve the establishment of about 1 million trees on
about 10 square miles of land. by the 15th year, along with
woody shrubs and herbaceoqs plants. The multiple uses
proposed for the project area include the following:
1.
Establishment of a reforested greenbelt to enhance the
environment of Maricopa County in harmony with
economic development planned by the Gila River
Indian Community.
2. Provision of borrow material for new highway
construction within the region being carried out or
planned by ADOT.
3. Establishment of a regional floodway with naturalistic
contours to convey, by gravity flow, excess storm
waters from South Mountain and East Valley
communities which are intercepted by the ADOT
highway system.
Preparation of this assessment and preliminaty plan was
supported by funding provided by the Flood Control District of
Maricopa County (FCD) and the Arizona Department of
TI3DSportation (AD01). Participants in the assessment and
planning process were the Gila River Indian Community
(GRIC), representatives of the FCD and ADOT, HDR
Engineering (a contractor to ADOt), and faculty members and
graduate students from Arizona State University's School of
Agnbusiness and Environmental Resources (ASU-SABER),
Department of Civil Engineering, and Office of Cultural
Resource Management.
Phase I of this project involved two major tasks: the
development of a (1) master plan/conceptual design and a (2)
revegetation plan.
The Gila Drain Master Plan was a multi-disciplinary effort
consisting of five sub-tasks: (i) a drainage report, (ii) a
stormwater yield study, (iii) a vegetative inventOlY, (iv) a land
use inventoty, and (v) a cultural resources reconnaissance.
1 Poster design and presentation by Jan Dillon, Graduate
Research Assistant and Project Coordinator, Arizona State
University, College of Engineering, School of Agribusiness &
Environmental Resources
306