抄録
As a continuation of the authors' previous report, this paper reports how the gronndwater level around the district concerned changes in accompany with the construction of Kashim a Port.
Having an area of about 70 km2, the district where the dug port will be constructed in a sandy seaside plain with a small part of sand dune. The thickness of aquifer is estimated at about 30m below the sea surface by boring. The port is provided with the main-route, the north-route and the south-route (Fig. 1).
The change of groundwater level after construction of the dng port can be estimated by the hydraulic method. However, the special feature of this report consists in obtaining the basic data by the hydrological method. The permeability coefficient in the large area can be directly obtained by the pumping test. Also it can be calculated from the groundwater flow (which is balanced with the groundwater supplied) and the groundwater table. Such groundwater flow is determined by the water balance method and is checked by the measured values of the groundwater seepage to the drainage canal.
Considering the shape of the port and the topography of the district, the change of groundwater level after the construction of the dug port is given by formula (1) available for a district surrounded by port, sea or river in a U-shaped form, by formula (2) for a district surrounded in a fanshaped form, and by formula (3) and (4) for a district surrounded in a semi-elliptical form. Formulas (1)-(4) are listed below:
_??_(1)
_??_(2)
_??_(3)
_??_(4)
The watershed is obtained if the formula (3) and (4) are equivalent and r= r1. The symbols used in these formulas are designated in Fig.6.
The values of groundwater flow G adopted in fomulas (1)-(4) are based on those obtained by the water balance of the southern part of Kashima (of the previous paper). Fig.7 was obtained by correcting the results estimated by formula (1)-(4) inaccordance with the practical conditions. The lowering of groundwater is shown in Fig. 8.The authers believe that it is very useful to apply the water balance and hydranlic methods together for the estimation of groundwater table after changes of general conditions have occurred.
