Terraces along the Asahi and Waga Rivers, Northeastern Honshu, Japan

The drainage areas of the Asahi and Waga Rivers compose a zone crossing the Backbone Ranges of Northeastern Honshu, Japan. In this area, the Backbone Ranges consist of two ranges, the eastern and western, with a lowland between them. From the central lowland, the Asahi River flows westwards through the western range to the Yokote Basin, and the Waga River flows eastwards across the eastern range to the Kitakami River Valley. Fluvial terraces are well developed along these two rivers and their tributaries. The borders of the drainage areas of the Asahi and Waga Rivers are situated on the gentle hills in the central lowland. The terraces are hardly traced beyond the divide. A gorge between the middle and lower courses of the Waga River prevents direct tracing of the terraces. The terrace sequences in three areas along the Asahi and its tributary, the Kurosawa River, along the upper and middle courses of the Waga River, and along the lower course of the Waga River are shown in Tables 1, 2, and 3, separately. The correlation of them (Table 4) was based on the altitude, geomorphology, and deposits of the terraces, especially on the characteristic features built by the minor tributaries and gullies which are thought to have climatic implication during their development. Further discussion concerning the Quaternary crustal movement in the present area will be given at another opportunity

Regional flood dynamics in a bifurcating mega delta simulated in a global river model

In this paper we show the importance of bifurcation channels for flow in river mega deltas through the use of a new computational scheme implemented in the CaMa-Flood global hydrodynamic model. First, we developed a new river network map based on SRTM3 and HydroSHEDS which includes bifurcation channels. Next we implemented a new bifurcation scheme in CaMa-Flood capable of routing flow along this network and used the model to simulate the Mekong River. We show that in the Mekong delta such channels route about 50% of total flow, and that their representation is essential for realistic hydrodynamic simulations. A simulation without bifurcation channels was obviously unrealistic because no flow occurred between the mainstem and adjacent channels even when their water level difference was >6 m. The bifurcation channels are extracted from globally-available datasets, thus it is straightforward to expand the proposed scheme to global-scale studies