The 6 mm day
À1 of daily evapotranspiration was converted to hourly evapotranspiration following the angle of insolation to the ground surface. The daily discharge
of 2 mm day
À1 , the bulk density of 0.17, and the field capacity of 0.7 volÁvol
À1 of
peat are used in this model. Three important hypotheses on water movement
between layers are applied in this model.
The first hypothesis is that the pattern of water use by root follows the pattern
shown in Fig. 19.11b. The evaporation and transpiration from the surface layer at UF
are set as 10%, and 90% of the water in the peat layer is used as transpiration from
the layer deeper than 10 cm in depth. Conversely, the water from the surface 10 cm
and the layer deeper than 10 cm are set to 60%, respectively, at DF. 100% of the
water in the peat layer is set to be used from the surface 10 cm at OG The second
hypothesis is the amount of water movement between two layers determined by the
difference between the water potential in both layers. Finally, the third hypothesis is
the water supply from the atmosphere just above the ground surface occurs during
nighttime.
The simulated results of the surface peat moisture at UF, DF, and OG are shown
in Fig. 19.12. The diurnal fluctuation patterns of moisture in surface peat at three
sites are very similar to the measured patterns. The decreases of peat moisture for
10 days were 0.045 volÁvol
À1 at OG and 0.03 volÁvol
À1 at DF, respectively, which
are very similar to those of the measured values. Yet, in the case of UF, the simulated
moisture reduction for 10 days was 0.025 volÁvol
À1 , which is clearly higher than that
of the measured amount. This large difference between simulated and measured
values is resolved by changing the discharge rate from 2 mmÁday
À1 to 1 mmÁday
À1 .
19.4 Hydrology in the Horizontal Geosphere
Typically, the groundwater head distributions and flux of the groundwater are
calculated by the governing flow Eq. (19.6). This equation is formulated by conservation of mass over a control volume of an aquifer situated in the flow field.
Moreover, this equation is based on Darcy’s law.
∂
∂x i
K i,j
∂h i
∂x j
¼ S s
∂h
∂t
þ q
ð19:6Þ
where i, j ¼ 1, 2, 3 (principal coordinate directions), K ¼ hydraulic conductivity in
[LT
À1 ], h ¼ head [L], Ss ¼ specific storage [L
À1 ], q ¼ local sources and sinks per
unit volume [T
À1 ], and t ¼ time in [T].
Simplification of Eq. (19.6) to horizontal two-dimensional equation, i.e. Dupuit–
Forchheimer assumption (Dupuit 1863; Forchheimer 1886) is adopted under the
assumption that the vertical flow can be negligible. The simplified Eq. (19.6) is
written below as Eq. (19.7), assuming that the vertical thickness of the aquifer is
b [L].
19 Principles of Hydrological Management of Tropical Peatland
553
À1 of daily evapotranspiration was converted to hourly evapotranspiration following the angle of insolation to the ground surface. The daily discharge
of 2 mm day
À1 , the bulk density of 0.17, and the field capacity of 0.7 volÁvol
À1 of
peat are used in this model. Three important hypotheses on water movement
between layers are applied in this model.
The first hypothesis is that the pattern of water use by root follows the pattern
shown in Fig. 19.11b. The evaporation and transpiration from the surface layer at UF
are set as 10%, and 90% of the water in the peat layer is used as transpiration from
the layer deeper than 10 cm in depth. Conversely, the water from the surface 10 cm
and the layer deeper than 10 cm are set to 60%, respectively, at DF. 100% of the
water in the peat layer is set to be used from the surface 10 cm at OG The second
hypothesis is the amount of water movement between two layers determined by the
difference between the water potential in both layers. Finally, the third hypothesis is
the water supply from the atmosphere just above the ground surface occurs during
nighttime.
The simulated results of the surface peat moisture at UF, DF, and OG are shown
in Fig. 19.12. The diurnal fluctuation patterns of moisture in surface peat at three
sites are very similar to the measured patterns. The decreases of peat moisture for
10 days were 0.045 volÁvol
À1 at OG and 0.03 volÁvol
À1 at DF, respectively, which
are very similar to those of the measured values. Yet, in the case of UF, the simulated
moisture reduction for 10 days was 0.025 volÁvol
À1 , which is clearly higher than that
of the measured amount. This large difference between simulated and measured
values is resolved by changing the discharge rate from 2 mmÁday
À1 to 1 mmÁday
À1 .
19.4 Hydrology in the Horizontal Geosphere
Typically, the groundwater head distributions and flux of the groundwater are
calculated by the governing flow Eq. (19.6). This equation is formulated by conservation of mass over a control volume of an aquifer situated in the flow field.
Moreover, this equation is based on Darcy’s law.
∂
∂x i
K i,j
∂h i
∂x j
¼ S s
∂h
∂t
þ q
ð19:6Þ
where i, j ¼ 1, 2, 3 (principal coordinate directions), K ¼ hydraulic conductivity in
[LT
À1 ], h ¼ head [L], Ss ¼ specific storage [L
À1 ], q ¼ local sources and sinks per
unit volume [T
À1 ], and t ¼ time in [T].
Simplification of Eq. (19.6) to horizontal two-dimensional equation, i.e. Dupuit–
Forchheimer assumption (Dupuit 1863; Forchheimer 1886) is adopted under the
assumption that the vertical flow can be negligible. The simplified Eq. (19.6) is
written below as Eq. (19.7), assuming that the vertical thickness of the aquifer is
b [L].
19 Principles of Hydrological Management of Tropical Peatland
553