15 Introduction to and General Aspects of Water Management
341
15.5.3 Flood spreading and groundwater recharge
The following example illustrates the use of remote sensed imagery for locating a
flood-spreading scheme for shallow groundwater recharge, to be used for local
irrigation. Colour Plate 15.B shows a color composite image of Landsat 5 Thematic
Mapper bands 4, 7 and I of a study area east ofFasa, Shiraz, Southern Iran. Episodic
flood nmoff in this region is lost to playas or to the sea. Some of that water can be
intercepted using a floodwater spreading scheme for artificial recharge, if three
criteria are satisfied: (a) the catchment must have an adequate size to generate
sufficient runoff, but not be too large to deal with high discharges for a simple
diversion, (b) the area of infiltration should be close to the ephemeral river and be
underlain by permeable deposits, and (c) the infiltrated water should recharge a
shallow aquifer from which the water can be pumped for irrigation. As can be seen
on the image, the criteria are met in this case. Peak flows from the moderately sized
catchment (shown in part) are diverted from the river where it flows on an alluvial fan
(A), into parallel diversion channels which feed - sandy - infiltration basins (B),
described in detail by Kowsar (1989). The evidence of an aquifer can be inferred from
the presence of groundwater irrigated fields at the lower part of the alluvial fan.
Geomorphological interpretation of the image leads to a differentiation of deposits of
small local fans (D), not of interest, the upper sandy part of the main alluvial fan (A)
suitable for a recharge scheme, and the lower part (C) with heavier soil textures. The
latter part may be less suitable for artificial infiltration, but has fewer losses of
irrigation water. A groundwater model was used for the assessment of the recharge.
15.6 Irrigation water management and remote sensing
It is estimated that the world's irrigated area is at present in the order of270 million
ha. This is only 17% of the world's total cropped area but accounts for about one third
ofthe world's food harvest (Smedema, 1993). Despite this important contribution to
agriculture, the performance of the irrigated agriculture sector has, in general, been
disappointing. A basic reason is the low efficiency in the use of available water
resources. In some projects, 60% of the diverted water does not actually contribute
to crop water requirements. Technical problems arise because irrigation water
supplies have not well been distributed. At the farm level, water supply may be
unreliable, supply and demands seem rarely to coincide or farmers practice poor and
inefficient irrigation methods.
Remote sensing techniques permit a quantitative analysis of problems associated
with poor water distribution in irrigation perimeters (Menenti et ai., 1989; Bastiaanssen & Molden, 1998). Inadequate water supply is clearly reflected in differences in
cropping patterns, intensities and crop development; features which can be conveniently detected and mapped by satellite images. Feasibility studies for improving
water distribution can make excellent use of this information.
It has been estimated (Umali, 1993) that about one-third of the irrigated land in the
world is under serious salinization risk. Mapping of salt affected or water logged
areas in large irrigation schemes, making conjunctive use of remote sensing data and
341
15.5.3 Flood spreading and groundwater recharge
The following example illustrates the use of remote sensed imagery for locating a
flood-spreading scheme for shallow groundwater recharge, to be used for local
irrigation. Colour Plate 15.B shows a color composite image of Landsat 5 Thematic
Mapper bands 4, 7 and I of a study area east ofFasa, Shiraz, Southern Iran. Episodic
flood nmoff in this region is lost to playas or to the sea. Some of that water can be
intercepted using a floodwater spreading scheme for artificial recharge, if three
criteria are satisfied: (a) the catchment must have an adequate size to generate
sufficient runoff, but not be too large to deal with high discharges for a simple
diversion, (b) the area of infiltration should be close to the ephemeral river and be
underlain by permeable deposits, and (c) the infiltrated water should recharge a
shallow aquifer from which the water can be pumped for irrigation. As can be seen
on the image, the criteria are met in this case. Peak flows from the moderately sized
catchment (shown in part) are diverted from the river where it flows on an alluvial fan
(A), into parallel diversion channels which feed - sandy - infiltration basins (B),
described in detail by Kowsar (1989). The evidence of an aquifer can be inferred from
the presence of groundwater irrigated fields at the lower part of the alluvial fan.
Geomorphological interpretation of the image leads to a differentiation of deposits of
small local fans (D), not of interest, the upper sandy part of the main alluvial fan (A)
suitable for a recharge scheme, and the lower part (C) with heavier soil textures. The
latter part may be less suitable for artificial infiltration, but has fewer losses of
irrigation water. A groundwater model was used for the assessment of the recharge.
15.6 Irrigation water management and remote sensing
It is estimated that the world's irrigated area is at present in the order of270 million
ha. This is only 17% of the world's total cropped area but accounts for about one third
ofthe world's food harvest (Smedema, 1993). Despite this important contribution to
agriculture, the performance of the irrigated agriculture sector has, in general, been
disappointing. A basic reason is the low efficiency in the use of available water
resources. In some projects, 60% of the diverted water does not actually contribute
to crop water requirements. Technical problems arise because irrigation water
supplies have not well been distributed. At the farm level, water supply may be
unreliable, supply and demands seem rarely to coincide or farmers practice poor and
inefficient irrigation methods.
Remote sensing techniques permit a quantitative analysis of problems associated
with poor water distribution in irrigation perimeters (Menenti et ai., 1989; Bastiaanssen & Molden, 1998). Inadequate water supply is clearly reflected in differences in
cropping patterns, intensities and crop development; features which can be conveniently detected and mapped by satellite images. Feasibility studies for improving
water distribution can make excellent use of this information.
It has been estimated (Umali, 1993) that about one-third of the irrigated land in the
world is under serious salinization risk. Mapping of salt affected or water logged
areas in large irrigation schemes, making conjunctive use of remote sensing data and