Abstract
Land use shows the interaction between human and nature, and its impacts especially on runoff have received global attention and required more research studies. However, watershed database is generally available only for very large scales and not yet adapted to small scales. This paper presents a methodology for watershed delineation and potential influence assessment of runoff on the small watersheds in Japan based on the locations of the official observatory point data. Flow direction, flow accumulation, snap pour point and watershed recognition were analyzed by using the D8 algorithm and 10 m × 10 m DEM data of Japan. Totally 3831 watersheds were delineated by defining snapping pour point distance of 50 m as the input value, and the nation-wide watershed database was established. According to the suggestion of Notification No. 521 from the Ministry of Land, Infrastructure and Transport of Japan and land use/land cover data from JAXA satellite Alos-2, comprehensive runoff coefficient (CRC) was calculated by the weighted average method and divided into 10 levels by the equal interval method using ArcGIS. The obtained watershed boundary lines were almost identical to the ridge lines in the mountain area which accounts for more than half of Japan. The CRC values in the biggest cities such as Tokyo and Osaka were the highest, indicating these cities would receive the highest impacts of runoff. These results can provide the technical support for the decision-making on watershed management. The creation of small-scale watershed database would provide basic materials for the subsequent research such as flood prevention, water shortage and biogeochemical cycle of the sustainable regional development.
Highlights
Water is regarded as the most important environmental resource for human survival and development (Khagram Clark, & Raad, 2003)
The objective of this study was to establish a watershed database in Japan, in association with the river water observation point based on its location
The observatory point data; which were plotted by the National Institute for Environmental Studies (NIES) of Japan based on the data of National Institute for Environmental Studies (2019) were used to get location information and find the contributing area watershed upstream
Summary
Water is regarded as the most important environmental resource for human survival and development (Khagram Clark, & Raad, 2003). Water-related measuring stations (including rivers, lakes and reservoirs) are usually set by the river (Pentland, Bathurst, & Sydor, 1980) which is constantly affected by potential hydrodynamic force. A large number of flooding occurred that are involved about structural engineering of flood infrastructure or meteorological change (Aktan et al, 1996) and related to many factors like long term runoff management in upstream area (Kean et al 2013). Water-related observatory is not set up on the outlet of the entire basin but somewhere near to the river to observe water quality, water level and flow rate, sometimes this is difficult for those concerned personnel to find the upstream contributing area to study the geographical element relationship across the watershed. Watershed delineation is a science (Jensen & Domingue, 1988; O’callaghan & Mark 1984; Verdina & Verdin, 1999) which can reveal all the geographical elements of their relationship inside watershed
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