Newsletter and Technical Publications
of Alternative Technologies for Freshwater Augumentation
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PART B. TECHNOLOGY PROFILES
1.6 Flow Diversion Structures
Diversion structures route runoff in excess of base flow to storage
facilities during wet periods, for later use during dry periods. Flood
diversion structures, such as dikes, are also useful methods for
mitigating the adverse effect of torrential rains and at the same time
capturing the excess water for later use. The following types of
structures have been used to divert flood water for water supply
Transverse dikes are built in sections along a river to store excessive
runoff. These dikes can be built using material dredged from the river or
transported from adjacent lands. The dike material, usually clay or silt,
must be highly compacted and in many cases it is advisable to place riprap
on the dike to increase its strength and protect it from erosion.
Diversion Structures (toroba)
Toroba are homemade diversion structures built of wooden poles,
taken from trees such as the curari and cuji in Venezuela,
vegetation residues, and logs. The wooden poles are 50 and 130 cm in
length and are placed at intervals of 50 cm to 70 cm to define a wall of
debris that will divert the runoff. This technique may also increase
infiltration to the groundwater.
Water traps are used to control the deleterious effects of runoff in a
river basin and to facilitate water storage and the re-charge of aquifers.
They are built like an earth dam, usually 1 m to 3 m high, using local
materials. The walls are compacted in 20 cm layers using the same
equipment as is used to build a dam. The edges are trapezoidal with an
embankment slope of 2.5:1 at high water and 2:1 at low water. The bottom
width of the water trap is 2.5 m. They are normally located across a river
bed, segmenting the channel into compartments. Water traps are usually
designed to handle runoff produced during a 1-in-50-year rainfall. The
volume of runoff captured depends upon the catchment area and the
intensity of the rainfall.
Extent of Use
Transverse dikes have been used on rivers in the State of São
Paulo and in the Serra do Mar region, Brazil. Water traps have been used
in arid and semi-arid regions, particularly in the Province of Mendoza,
Argentina. They have been very useful in reducing sedimentation and
limiting the risk of flooding. Toroba are used in the State of
Falcón, Venezuela. This technique has limited utility, but can be
helpful in rural areas that lack technical resources.
Operation and Maintenance
The operation of these types of diversion structures is very simple.
They require continual maintenance to repair damage caused by large storms
and to control erosion, especially around the abutments, which can breach
the dikes and water traps and significantly damage the homemade
Water traps require maintenance during the first few years of operation,
until natural vegetation grows again in the area. When rains heavier than
the design flow conditions occur, it is possible that the traps will be
breached and will need to be rebuilt. All-terrain recreational vehicles
used in areas at or near the water traps can cause damage that may need
additional maintenance or repair.
Figure 12: A Schematic Representation of a Homemade
Structure (Toroba) in Venezuela.
Martínez, FUDECO, Barquisimeto, Venezuela.
Level of Involvement
Homemade structures can be built, operated, and maintained by
local communities but may require technical assistance from government
agencies and/or nongovernmental institutions and the private sector. Dikes
and water traps require the participation of the government and private
sector, primarily in management of the volume of water retained behind
these structures and in ensuring their safe and sound construction.
The construction costs of dikes can range from $10 000 to millions of
dollars, depending on the size of the river, the length and width of the
dikes, and the scale of the project. The cost of homemade structures is
minimal, since all of the materials are locally available. The cost of a
small water trap in Argentina has been estimated at between $130 and $170.
Effectiveness of the Technology
Diversion structures are very effective in reducing sediment erosion,
retaining runoff, and encouraging groundwater infiltration. Water traps
have been successfully used for more than 25 years in Argentina. They have
been very useful in controlling sedimentation, and reducing the risk of
flooding, within river basins.
Diversion structures are suitable for use in river basins where
sufficient volumes of water can be diverted and stored for later use.
Areas like Serra do Mar in southeastern Brazil, Falcón State in
Venezuela, or the San Juan River basin in Argentina are typical areas well
suited for the application of this technology.
- Diversion structures enable the use of water that normally would run
- Diversion structures provide some in-stream control of erosion and
- Diverted water may serve as a source for groundwater recharge.
- Water velocities in river channels are reduced.
- Soil fertility is improved by retaining water on the land surface and
reducing soil loss.
- Retention of runoff may contribute to biodiversity and ecosystem
restoration by reducing erosion and retaining water on the land surface.
- Construction of diversion structures may disrupt vegetation.
- Structures may be breached by storms that exceed the design
- Structures may adversely affect aquatic flora and fauna by altering
flow patterns and flooding regimes.
Flow diversion structures are widely accepted among the
engineering community as a method to control erosion and sedimentation,
and augment water supply. Greater acceptance by local communities could
yield substantial local benefits.
Further Development of the Technology
It is important that more data on the performance and problems of
diversion structures be acquired in order to assess and suggest possible
improvements. Greater educational programming on the use of this
technology as a tool for river basin management should be planned and
Alberto I. J. Vich, Armando R. Pedrani, and Adriana
Mariani, Programa de Investigación y Desarrollo Manejo Ecológico
del Piedemonte, Instituto Argentino de Nivología, Glaciología
y Ciencias Ambientales, Unidad Ecología y Manejo de Cuencas Hídricas,
Casilla de Correo N° 330, 5500 Mendoza, Argentina. Tel. (64-61)
28-7029. Fax (64-61) 28-7029 / 28-7370. E-mail: firstname.lastname@example.org.
Marco Antonio Palermo, Departamento de Aguas y Energia
Elétrica do Estado de São Paulo (DAEE), Rua do Riachuelo
115, sala 415, 01007-000 São Paulo, Brasil. Tel. (55-11)974-0350 /
258-4595. Fax (55-11)258-4595.
Carmen Fermín, Dirección de Hidrología y
Meteorología, Ministerio del Ambiente y de los Recursos Naturales
Renovables (MARNR), Esquina Camejo, Edificio Camejo, 5° piso,
Caracas, Venezuela. Tel. (58-02)408-1952. Fax (58-2)545-0607. E-mail:
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