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Management
of water for irrigation is increasingly becoming an issue of concern on the
Santa Ana reservation. The conveyance and diversion of water to irrigated land
needs major improvement. No structures for measuring water is currently
available in the system in order to raise the head of water to supply to
farmers. Focus: To line irrigation ditch
and to install measuring structures. Background There is
2,560 acres of land on the reservation that can be irrigated. The length of the irrigation ditch is
approximately six miles long by 5ft wide and 5ft deep. A high percentage of
water in the ditch is lost due to rodents, seepage in to the sandy soil, and
due to erosion of the banks. Other major loss of water may be due to
evapotranspiration. Due to these losses
there is not enough water delivered down stream for irrigation. This is a major concern to the growing
demand of agriculture on the reservation. The current ditch for delivering
water for irrigation is an earth-type channel. Earth
channels are designed and constructed with non-silting and non-scouring
velocities in order to achieve a desirable regime section yet excessive
sedimentation and scouring is perhaps the most common problem affecting the
performance of the entire system due to the following reasons: ·
Excessive sediment entry from the reservoir into the main
canal; ·
Disproportionate withdrawals of sediment by branch canals; ·
Disproportionate withdrawals of segment by outlets; ·
Improper side slopes and berms in deep cut reaches; ·
Prolonged running of canals with discharges less than the
designed full supply discharge, causing lower velocities and consequent
deposition of sediment; ·
Excessive weed growth which chocks sections of the
irrigation channels, reducing the velocity of flow and causing the deposition
of sediment; ·
Drifting of sand; ·
Prolonged heading-up at control points, which reduces up
stream velocities; ·
Haphazard desilting during maintenance; ·
Re-ertry of excavated earth and silt by rain and wind; ·
Prolonged running of canals with excessive discharge
causing higher velocities of flow and consequent eroding of sides and bed of
the canal; ·
Improper regulation of control structures, which also
cause erosion of canal banks and bed; ·
Damaged structures, especially overfalls, can cause much
downstream erosion; and, ·
Canal banks become eroded from animal pathways and heavy
rainfall. The greatest contributing factor
to high seepage losses in earthen channels is the biological life existing in
the cannel banks. Methodology
I would like to
solve this problem of conveying water for irrigation as follows: 1) Lining
the irrigation ditch with concrete. 2) Set up
measuring devices along the irrigation ditch. 3) Set up
operation and maintenance for the system. Concrete lining
Irrigation
ditches are lined to reduce roughness and increase velocity of flow, and to
reduce seepage losses. Concrete is commonly used as a lining material for a
canal. The concrete lining is strong enough to take care of erosion to sides
and bed, also reduces maintenance. Water will be delivered to the land faster
and could be distributed among the farmers more efficiently if the irrigation
ditch is lined with concrete. The design flow velocity is such that it does not
allow sediment deposition except near cross regulators. Therefore, it requires little maintenance,
provided it has been properly constructed. The routine maintenance activities
are replacement of joints, slabs, and weed control in joints. However,
if lining is not properly designed and constructed, then it creates maintenance
problems. Backwater, or subsurface water pressure behind the lining, can cause
cracks and bulging with eventual eruption of the lining. Sometimes, damage to
the lining is so extensive that repairs cannot be performed as routine
maintenance. Measuring Structures
To properly
deliver appropriate amount of water to the farmers, structural devices for
raising the head of water and measuring the flow is necessary. Irrigation system
operators commonly use many types of standard water measurement devices that
could be installed in this canal. These
devices are currently available at a reasonable cost and are known to function
efficiently such as those at Elephant Butte Irrigation District (EBID).
One type of
measuring device is the Cipolletti Weir. A standard Cipolletti weir is
trapezoidal in shape. The crest and sides of the weir plate are placed far
enough from the bottom and sides of the approach channel to produce full
contraction. A measuring weir is simply an overflow structure built
perpendicular to an open channel axis to measure the flow rate of water.
Inspecting and checking the critical parts of weir structures for degradation
and improper operation are easy. A properly built and operated Cipolletti weir
has a unique depth of water at the measuring station in the upstream pool for
each discharge. The crest overflow shape governs how the discharge varies with
head measurement . Weir Sticks are commercially calibrated stick or staff gage
type devices which may be placed upon the crest of a weir. The stick shows dept
of flow plus velocity head or the roundup of water above the water surface at
the weir blade. On this six
mile channel, three Cipolletti weirs would be built, one at he start of the
channel one somewhere in the middle, and one towards the end. Maintenance
·
Normal or Routine- Refers to
the usual maintenance activities that are conducted annually for an irrigation
system. Normal maintenance involves activities commonly done every year.
·
Emergency – When unusual conditions occur
that jeopardize the safety of the channels then the required maintenance is
termed emergency because of the urgent need to take immediate action.
·
Essential Structure Maintenance- Is the required maintenance for flow control structures
that will also allow the structures to be used for discharge measurement after
calibration.
·
Deferred Maintenance- Is the
accumulation of maintenance needs being accrued under the normal or routine
maintenance.
·
Catch-up Maintenance- Is a program
for taking care of the accumulated Priority Deferred Maintenance in order to
upgrade the hydraulic performance of the system.
·
Preventive Maintenance- Is a program
for taking care of the causes creating the maintenance needs when they are only
a minor problem, rather than allowing such maintenance to go unattended until
they become a major and expensive problem.
·
Rehabilitation- Is required
because the accumulation of deferred maintenance needs has become so grate that
the operation of the irrigation system is significantly hampered.
With the management of water for irrigation becoming a
concern, now is the time to apply for funding through different grants that may
be available to the tribe. It is important that we start conserving or water
resources. At the present time we take for granted the use of our irrigation
water, but in the very near future we will be faced with using only what is
allotted to each individual farmer, so as a tribe we should start considering
alternatives.
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