山地小流域内の地温年変化について

Abstract

渓流水温の形成を考えるには流域内の地中の熱交換過程を明かにする必要がある。そこで, 流域内の地温を桐生試験地内の7個所で測定した。全国各地の5個所の森林測候所での測定値と合わせて検討した結果は次のとおりである。1. 水移動の影響を無視し得る1次元均質な半無限固体における熱伝導理論の地温伝播に対する適合性を検討した。森林測候所の中には適合性の良くないところもあったが, 桐生等では適合性は良好で, 桐生の温度伝導率は6×10_-3cm_2sec_-1の値が得られた。2. 林外及び林内別に, 地表面地温の年変化特性を下層の地温より推定し, それぞれの地点の気温と比較した。地表面地温と気温の関係は林外と林内では異るものであった。3. 林外気温と林内気温の年変化を比較したところ, 平均値, 振幅, 位相はほぼ一致した。4. 桐生のデータにより, 水移動の地温年変化に与える影響を検討した。水温の年変化において, 振幅と位相の関係は, 水移動を無視し得る1次元均質な半無限固体における熱伝導理論より導びかれる両者の関係と異るものであった。桐生の一部の地温にもそのような傾向がみとめられた。これらの結果は水温形成の研究にひとつの重要な情報を与えるものである。

To consider the formation of stream temperature, it is necessary to make clear the process of the heat exchange under the ground in the watershed. For that purpose, we observed soil temperatures in a watershed, Kiryu in a weathered granite mountain, and examined both these data and those observed at the 5 meteorological observatories in the mountain districts of Japan. The outline of the investigation is discribed below. 1) We examined the applicability of the theory of conduction of heat in a homogeneous semiinfinitive one-dmiensional solid, where effects of water movement are neglected, for the soil temperatures. Although the condition of thermal diffusion was not satisfactory at some observatories, the theory of conduction was applied at the others and Kiryu. The value of thermal diffusivity was 6×10-3 cm2 sec-1 in Kiryu. 2) We estimated annual variations of the soil surface temperatures, and compared them with those of the air temperatures. The relation between them outside of the forest was different from those in the forest. 3) We compared annual variations of the air temperatures outside of the forest with those in the forest. Each of the annual mean value, amplitude and phase outside of the forest was nearly equal to that in the forest. 4) We investigated effects of water movement on annual variations of the soil temperatures in Kiryu. The relation between amplitude of the water temperature and its phase was different from the relation induced from the theory of conduction of heat in a homogeneous semiinfinitive one-dimensional solid where effects of water movement are neglected. Such a tendency was recognized in the soil temperatures at some points. These results give one of the important informations to the study on the formation of water temperature in a watershed.