24-08-2012, 03:44 PM
Structural Design of Concrete Lined Flood Control Channels
Design of Concrete Flood Channels.pdf (Size: 513.09 KB / Downloads: 194)
Introduction
Purpose and Scope
a. Purpose. This manual provides guidance for the
design of reinforced, concrete lined flood control channels
which convey rapid and tranquil storm water flows to
prevent flooding. This guidance presents provisions for
coordinating the disciplines involved in the design of
channels, selecting channel type, and identifying the critical
aspects of designs which require quality assurance
inspection during construction. Channel design involves
determining the overall channel configuration including
appurtenant structures, designing reinforced concrete
structures and pavement or concrete lining, determining
type and location of joints, designing subdrainage systems,
and designing appropriate safety features.
Coordination
Although this guidance pertains primarily to the structural
design aspects of flood control channel design, close
coordination with other design disciplines and the local
sponsor is required. Other disciplines involved in the
design are hydrologic, hydraulic, concrete and materials,
geotechnical, environmental, and construction. Some of
the critical aspects of the design process which require
coordination are:
a. Estimates of design slope and runoff volumes,
selection of channel cross-sectional area, and location of
required energy dissipation and juncture structures.
Channel Section
The proper cross section for a reach of channel is one that
provides adequate hydraulic capacity at the minimum cost.
Economic considerations for selecting the channel section
include the costs of design and construction, right-of-way,
required relocations, and maintenance and operation. A
trapezoidal channel is usually the most economical channel
when right-of-way is available and is, therefore, the
more commonly used channel section. A rectangular
channel may be required for channels located in urban
areas where the right-of-way is severely restricted or
available only at a high cost.
Safety Provisions
Channel designs should include safety provisions for the
needs of the public and operations personnel. Local sponsors
are responsible for the safe operation of channels,
and designers should coordinate designs with the sponsor
so that appropriate provisions are incorporated to ensure
safe operation of the project. Railing or fencing should
be provided on top of rectangular channel walls and walls
of chutes or drop structures for public protection. Ladders
should be provided on the sides of rectangular channel
walls and steps provided on the sloped paving of
trapezoidal channels to provide safe access for operations
personnel.
Selection of Channel Type
Paragraph 1-6 identifies the hydraulic capacity as the
primary functional consideration and the costs of
right-of-way, relocations, construction, and operation as
economic considerations for selecting channel type.
Existing site developments, existing geophysical site
conditions, and performance or service requirements
impact the selection of channel type and the resulting construction
costs. The construction cost of trapezoidal
channel sections is less than that of rectangular sections.
Generally, the lowest cost of erosion protection is sod,
and the cost increases with riprap protection and even
more when reinforced concrete paving is used. Typical
trapezoidal channel types are shown in Figure 2-1.
Drainage Provisions
Drainage systems should be provided to control excessive
hydrostatic pressures acting on the concrete structures of
lined flood control channels where the permanent water
table is above the channel invert. These systems should
also be provided where the temporary water table is
expected to be above the channel invert due to local
ponding or seasonal variations.
a. Drainage systems. Drainage systems used in past
designs include open, closed, and weep-hole systems.
Open drainage systems consist of collector drains which
drain through weep holes in the channel lining. The
collector drains are encased with a graded filter to prevent
blockage of the drain or removal of the foundation material.
Maintenance During Operation
Proper maintenance of flood control channels is essential
to satisfactory performance. This requires periodic
inspection of the channels, including the concrete linings,
appurtenant concrete structures, and the subdrainage system.
Current Corps Operations & Maintenance (O&M)
provisions require that flood control projects be inspected
periodically. The frequency of project inspections and
other operation and maintenance requirements shall be
identified in the project O&M Manual. Any deficiencies
critical to the function of the project should be corrected
with urgency. Broken concrete and cracks in the concrete
which are wide enough to cause concern should be
repaired. Subdrain systems that are clogged shall be
cleaned.