No abstract

The Song Hong (Red River) delta, northern Vietnam, is characterized by huge natural levees in an area of the delta plain known as the West Floodplain where fluvial sedimentation predominates. The natural levees along the Day River, a major distributary of the Song Hong, are comparable in size with those of the main course of the Song Hong. The Day River levees are 3–8 km wide and rise 2–5 m above the adjacent backswamps and have played an important role in human settlements since the late Metal age. We discussed the relationships among the natural levees of the Day River, delta progradation and the distribution of archaeological sites on the delta plain. During the early Holocene, the accumulation of sediment discharged by the Song Hong enhanced both aggradation of the floodplain and river mouth progradation within the drowned valley of the Song Hong. Radiocarbon dates from cores, trench exposures, and archaeological sites record a dramatic slowing of aggradation when sea level stabilized during 6–4 cal. kyr BP (the Holocene sea-level highstand). As sea level fell to the present level during 4–0 cal. kyr BP, the river mouth prograded rapidly toward the Gulf of Bac Bo (Gulf of Tonkin) and the river channels extended seaward. In the West Floodplain, lateral accretion overtook vertical accretion to generate the present longitudinal profiles of the Song Hong and Day rivers. During this period, human settlements spread across the backswamp and Holocene terrace area, lagging around 2 kyr behind the shoreline migration.

No abstract

A ground source heat pump (GSHP) system has higher cooling and heating performances than an air source heat pump system, so the GSHP system has attracted attention in the cold regions. Particularly after the 2011 earthquake off the Pacific coast of Tohoku, which damaged nuclear power plants, the GSHP utilizing renewable energy, has become attractive in heating system in the Tohoku region. However, it is necessary to install wells to collect ground source heat, and so, together with the cost of the heat pump itself, the installation cost is a barrier to widespread adoption of this technology in Japan. On the other hand, due to poor subsoil, foundation piles are often required in the construction of buildings in Japan. By using foundation piles as heat exchangers, which are commonly used in residential construction, the cost of using GSHP systems in houses may be reduced. However, since the placement of the piles depends on the floor layout of the residence, that is arbitrary sequence. Moreover, an arbitrary floor layout requires a complicated multi-dimensional numerical analysis to design the GSHP, and the analysis is burdensome for general designers. Therefore, the use of the model unit of the two-dimensional cylindrical heat exchange well is proposed. The use of this model, which includes an unused volume of soil, reduces the analysis burden for general design tools. On experience, the arrangement rate is 4 m2 per pile, and the well separation is narrow. And the foundation piles will form a group. So thermal interference between heat exchanger wells might be working hard. In addition, the foundation piles are very short, compared to the traditional borehole depth of 50 to 100 m. Therefore, the thermal performance of the well may degrade compared to that of the traditional GSHP system, although the initial costs are less. Therefore, we examined a GSHP system with heat exchanger piles by using the heat exchange well unit model for residences in the Tohoku region. As a result, the two-dimensional analysis and more is needed to predict the thermal performances of the heat exchanger piles so that the effect of the pitch of the heat exchange wells on the heat transfer in the axial direction will be large. In cold climates, the heating demand is large and, in the summer, the amount of waste heat to the ground is small, so a large amount of heat penetration into the ground from the atmospheric air is important for continuous GSHP operation in the Tohoku region, and in Fukushima Prefecture in particular.

The Kumozu River delta, in central Japan, is a fluvial-wave dominated delta facing Ise Bay in the Pacific Ocean. We reconstructed the Holocene evolution of the Kumozu River delta area in response to sea-level changes using sedimentary facies analyses, grain-size analyses, and radiocarbon dating of two new cores, KM and KM , obtained from the delta plain as well as previously published data. The core sediments, in ascending order, consisted of fluvial gravelly sand, tidemud and upward-coarsening delta-front muddy sand, and modern fluvial sand and mud. The maximum flooding surface (MxFS) was identified between the estuarine and deltaic sediments, and was dated at about calibrated radiocarbon years ago (cal kyr BP). At that time the shoreline was located near the site of core KM , about km inland from the present shoreline. Before the MxFS, the present delta area was a fluvial environment until cal kyr BP, and then changed to an estuarine environment during cal kyr BP. After the MxFS, the Kumozu River delta formed and prograded eastward in the incised valley between Pleistocene terraces during cal kyr BP. After deltaic sediments filled the incised valley, the delta advanced into Ise Bay and became lobate. Delta-front migration shows that the delta prograded northeastward, mainly during and cal kyr BP, and southeastward during cal kyr BP.