Rice Irrigation Systems for Tailwater Management (4/7)
J.E. Hill, S.C. Scardaci, S.R. Roberts, J. Tiedeman, J.F. Williams
Static Irrigation System
The static irrigation system keeps pesticide treated water out of public
drains and eliminates the need for a tailwater sump and return pump as
used in the recirculating system. This system independently controls inflow
water into each basin and limits it to the extent required to replenish
the water lost to evapotranspiration and percolation. It also eliminates
the possibility of spillage of field tailwater into public drains. This
is a recent innovation in rice irrigation.
| Figure 4. Schematic diagram of a static water system. |
 |
 The static
system consists of a supply/drain ditch that runs perpendicular to the
levees in the field, serving each basin independently (fig. 4). The ditch
is separated at each levee by flashboard drop pipes that control ditch
and basin water depths (fig. 5 and fig. 4, profile).
 |
Figure 5. Flashboard drop pipe in the supply ditch. |
Water enters each
basin near these drop pipes through flapgated inlet pipes (fig.6). The
flapgates allow water to enter each basin when water in the supply ditch
is higher than in the corresponding basin. However, when water in the ditch
is lower than the basin, the flap closes and prevents reverse flow from
the basin. This keeps treated field water out of the supply ditch. Because
the supply ditch water is fresh, it generally does not contain any pesticide
residues from the field. Therefore, any excess spill from the ditch is
clean water.
| Figure 6.
Flap-gated inlet pipe in static water system. |
 |
In an emergency,
the supply ditch can also be used as a drain. The weir boards can be pulled
and the inlet flaps propped opened manually to allow field water out. Under
these circumstances, and at harvest, the ditch serves as a drain.
This system
has several advantages over other irrigation systems. Basins flood faster
than other irrigation systems due to multiple intakes, which also allows
for independent irrigation of individual basins. Also water changes can
be initiated almost immediately and completed without affecting the water
in neighboring basins thus allowing for increased management flexibility.
Because inflow
water is partially warmed in the supply ditch and does not flow through
and out of the basin, the deleterious effects of cold water on rice are
minimized and the need for a warming basin is eliminated. Herbicide efficacy
may be improved since field water flow is greatly reduced.
Disadvantages
of this system include land out of production for the ditch and the need
to control weeds in the ditch. Also, the system may not provide adequate
flushing in fields with alkali soil or that utilize saline irrigation water.
Costs of the
static irrigation system are associated with the construction of the supply/drainage
ditch, the flashboard drop pipes, and flapgate inlet pipes (one of each
for each basin). The cost of installing this system has averaged $95 (1990
dollars) per acre for 6 to 10 acre basins. Cost per acre should drop proportionately
for larger basins. Additionally, the ditch takes up about a 20-foot-wide
strip along the side of the field. There are no pumping costs as for recirculating
systems.
Table 3 presents
the advantages and disadvantages of a static irrigation system.
| Table 3. Static irrigation systems for rice
production in California |
| Advantages: |
Tailwater and pesticide residues can be contained on the field or farm
during growing season |
|
Cost of recirculating pumps is eliminated |
|
Independent control of each basin provides greater management flexibility
than flow-through system |
|
Precise water management is easier than other systems |
|
Agricultural chemicals stay where applied; improved herbicide effectiveness |
|
Well suited for Londax® application specifications |
|
Less cool water inflow reduces cold water effects on rice and the need
for a warming basin |
|
Crayfish burrowing around irrigation inflow structures is reduced |
|
| Disadvantages: |
Ditch construction, flashboard drop pipe, and inlet pipes with flaps are
costly |
|
The supply/drain ditch reduces land area available for crop production |
|
Reduced flushing |
|
Irrigation system is not suitable for many rotation crops because fields should be leveled to zero grade |
|
Weeds must be controlled in supply/drain ditch |
|
Comments to jayoung@ucdavis.edu