According to Vorob’eva and Pankova (2008), ESP increased to 50% or higher
when the pH (H 2 O) value was 9.5 or higher. Similar results were obtained using
selected samples from the muddy tsunami deposit. As a large amount of Na 2 CO 3
was necessary to raise the ESP values higher than 50%, it was estimated that the ESP
values of the tsunami-affected deposit in the humid region hardly rise higher than
50%.
6.2.7 Desalinization and Restoration of the Tsunami–
Affected Farmland
The tsunami-affected area is under a humid and temperate climate. Natural rainwater
will gradually remove salts from the soil. On the other hand, lowland soils, peat soils,
and muck soils are distributed in the region (Fig. 6.5c), and the groundwater level is
mostly high. Drainage water was pumped out near the major river mouths of the
central and southern part of Miyagi Prefecture, although the pumping system was
destroyed by the tsunami. Under these conditions, Figs. 6.14 and 6.15 show an
example of the vertical distribution of salts in paddy field with the passage of time.
This study site is located 3 km inland from the shoreline. The EC(1:5) value of the
muddy tsunami deposit (4 cm thick) was 9.2 dS m
À1 on June 15, 2011 (Fig. 6.14a),
and a portion of salts reached a depth of 36 cm from the surface. This date was
3 months after the tsunami, and a total of 250 mm of rainwater had fallen. The EC
(1:5) values of the tsunami deposit and the Ap horizon soil were lowered to around
1.5–2 dS m
À1 by September 4, 2011 (Fig. 6.14b), by natural rainwater (Fig. 6.14d).
Although the tsunami deposit was removed from the paddy field after this time, the
EC(1:5) values were reduced further to values lower than 0.6 dS m
À1 , a safe level for
mesophytes, by natural rainwater to the depth of 20 cm by June 24, 2012.
After removal of the soluble salts in the liquid phase by natural rainwater, Na
+
held on the exchange sites of the soil still tended to remain (Fig. 6.15b, c) whereas
EC(1:5) values were lowered (Fig. 6.14c). The low exchangeable Na
+ values at the
depth of around 30–40 cm are due to the insertion of a sand layer (Fig. 6.16a).
To restore the farmland damaged by the tsunami, debris from damaged homes,
fallen trees, and excessive salts had to be removed. The tsunami deposits have also
been removed from the farmland in Miyagi Prefecture. A portion of the Ap horizon
may have been removed during this operation. Irrigation water was finally used to
remove salts to a safe level. Soil from nearby mountains was dressed to refill the
original farmland level. A reduction in soil fertility was improved by the application
of fertilizer.
There have been many studies pertaining to salt-affected farmlands and rehabilitation (Agus and Tinning 2008; Nakaya et al. 2010). The drainage system, including
the underground one, plays an important role in desalinization by both rainwater and
irrigation water. In addition, in this study region, the ground along the coastal areas
6.2 Effects of Tsunami on Soils
149
when the pH (H 2 O) value was 9.5 or higher. Similar results were obtained using
selected samples from the muddy tsunami deposit. As a large amount of Na 2 CO 3
was necessary to raise the ESP values higher than 50%, it was estimated that the ESP
values of the tsunami-affected deposit in the humid region hardly rise higher than
50%.
6.2.7 Desalinization and Restoration of the Tsunami–
Affected Farmland
The tsunami-affected area is under a humid and temperate climate. Natural rainwater
will gradually remove salts from the soil. On the other hand, lowland soils, peat soils,
and muck soils are distributed in the region (Fig. 6.5c), and the groundwater level is
mostly high. Drainage water was pumped out near the major river mouths of the
central and southern part of Miyagi Prefecture, although the pumping system was
destroyed by the tsunami. Under these conditions, Figs. 6.14 and 6.15 show an
example of the vertical distribution of salts in paddy field with the passage of time.
This study site is located 3 km inland from the shoreline. The EC(1:5) value of the
muddy tsunami deposit (4 cm thick) was 9.2 dS m
À1 on June 15, 2011 (Fig. 6.14a),
and a portion of salts reached a depth of 36 cm from the surface. This date was
3 months after the tsunami, and a total of 250 mm of rainwater had fallen. The EC
(1:5) values of the tsunami deposit and the Ap horizon soil were lowered to around
1.5–2 dS m
À1 by September 4, 2011 (Fig. 6.14b), by natural rainwater (Fig. 6.14d).
Although the tsunami deposit was removed from the paddy field after this time, the
EC(1:5) values were reduced further to values lower than 0.6 dS m
À1 , a safe level for
mesophytes, by natural rainwater to the depth of 20 cm by June 24, 2012.
After removal of the soluble salts in the liquid phase by natural rainwater, Na
+
held on the exchange sites of the soil still tended to remain (Fig. 6.15b, c) whereas
EC(1:5) values were lowered (Fig. 6.14c). The low exchangeable Na
+ values at the
depth of around 30–40 cm are due to the insertion of a sand layer (Fig. 6.16a).
To restore the farmland damaged by the tsunami, debris from damaged homes,
fallen trees, and excessive salts had to be removed. The tsunami deposits have also
been removed from the farmland in Miyagi Prefecture. A portion of the Ap horizon
may have been removed during this operation. Irrigation water was finally used to
remove salts to a safe level. Soil from nearby mountains was dressed to refill the
original farmland level. A reduction in soil fertility was improved by the application
of fertilizer.
There have been many studies pertaining to salt-affected farmlands and rehabilitation (Agus and Tinning 2008; Nakaya et al. 2010). The drainage system, including
the underground one, plays an important role in desalinization by both rainwater and
irrigation water. In addition, in this study region, the ground along the coastal areas
6.2 Effects of Tsunami on Soils
149