Norio Hayakawa

Hydrological and geocryological response of winter streamflow to climate warming in Northeast China

Abstract An abrupt warming of regional climate with a 1.3 °C rise in annual air temperature, coupled with an increase of 20–40% in precipitation, has occurred in the 1990s in the permafrost region of Northeast China. The geocryological and hydrological responses of a river basin at high latitude and at altitude with some permafrost are detected based on monthly climatological and streamflow data for 40 years (1958–1998). The variation in depth of the active layer is estimated by an empirical model using annual air temperature, its annual amplitude and the maximum thickness of snow cover. Significant responses of winter streamflows to a 2.4 °C of air temperature warming during December to February were observed. This was especially true for the greatest warming (4.4 °C in February during the 1990s) when runoff increased by 80% in February and by 100% in March from the prior. These responses are caused by a change in depth and temperature of the active layer ranging from 1.5 to 3.0 m in areas where the drainage of the unfrozen water can occur when the ground temperature rises above 0 °C from −0.8 °C in February and March. The depth of the seasonal frost has shrunk by about 30 cm and the active layer thickness increased by about 40 cm in permafrost in the 1990s because of the warmer climate. The hydrological response from winter streamflows in permafrost areas is more significant and quicker than that from the seasonal frost areas. The freezing and drainage of ground water at 2.0–3.0 m deep in March is very sensitive to the climatic warming.

Analysis of Inclined Wall Plume by the k-ε Turbulence Model

The similarity solution of inclined wall plume is obtained analytically. The mathematical model used herein consists of the continuity equation of flow, the momentum balance equation in the flow direction, the diffusion equation of concentration, the equation of kinetic energy of turbulence and the equation of viscous dissipation rate of turbulence. It is shown that this set of equations has the similarity solution which can be solved numerically for each angle of the inclined wall. This numerical model is applied to the wide range of the slope angle, which includes the vertical wall plume as the special case and the nearly horizontal wall plume. The velocity and concentration profiles of the inclined wall plume are explained well by the similarity solutions.

NUMERICAL SIMULATION OF WAVE FIELDS AROUND THE SUBMERGED BREAKWATER WITH SOLA-SURF METHOD

Detailed studies have been undertaken to assist in the design of major extensions to the port of Haifa. Both numerical and physical model studies were done to optimise the mooring conditions vis a vis the harbour approach and entrance layout. The adopted layout deviates from the normal straight approach to the harbour entrance. This layout, together with suitable aids to navigation, was found to be nautically acceptable, and generally better with regard to mooring conditions, on the basis of extensive nautical design studies.Hwa-Lian Harbour is located at the north-eastern coast of Taiwan, where is relatively exposed to the threat of typhoon waves from the Pacific Ocean. In the summer season, harbour resonance caused by typhoon waves which generated at the eastern ocean of the Philippine. In order to obtain a better understanding of the existing problem and find out a feasible solution to improve harbour instability. Typhoon waves measurement, wave characteristics analysis, down-time evaluation for harbour operation, hydraulic model tests are carried out in this program. Under the action of typhoon waves, the wave spectra show that inside the harbors short period energy component has been damped by breakwater, but the long period energy increased by resonance hundred times. The hydraulic model test can reproduce the prototype phenomena successfully. The result of model tests indicate that by constructing a jetty at the harbour entrance or building a short groin at the corner of terminal #25, the long period wave height amplification agitated by typhoon waves can be eliminated about 50%. The width of harbour basin 800m is about one half of wave length in the basin for period 140sec which occurs the maximum wave amplification.Two-stage methodology of shoreline prediction for long coastal segments is presented in the study. About 30-km stretch of seaward coast of the Hel Peninsula was selected for the analysis. In 1st stage the shoreline evolution was assessed ignoring local effects of man-made structures. Those calculations allowed the identification of potentially eroding spots and the explanation of causes of erosion. In 2nd stage a 2-km eroding sub-segment of the Peninsula in the vicinity of existing harbour was thoroughly examined including local man-induced effects. The computations properly reproduced the shoreline evolution along this sub-segment over a long period between 1934 and 1997.In connection with the dredging and reclamation works at the Oresund Link Project between Denmark and Sweden carried out by the Contractor, Oresund Marine Joint Venture (OMJV), an intensive spill monitoring campaign has been performed in order to fulfil the environmental requirements set by the Danish and Swedish Authorities. Spill in this context is defined as the overall amount of suspended sediment originating from dredging and reclamation activities leaving the working zone. The maximum spill limit is set to 5% of the dredged material, which has to be monitored, analysed and calculated within 25% accuracy. Velocity data are measured by means of a broad band ADCP and turbidity data by four OBS probes (output in FTU). The FTUs are converted into sediment content in mg/1 by water samples. The analyses carried out, results in high acceptance levels for the conversion to be implemented as a linear relation which can be forced through the origin. Furthermore analyses verifies that the applied setup with a 4-point turbidity profile is a reasonable approximation to the true turbidity profile. Finally the maximum turbidity is on average located at a distance 30-40% from the seabed.

Analysis of powder-snow avalanches using three-dimensional topographic data

A fluid-dynamical model of powder-snow avalanches is developed which takes into account three-dimensional topography and can compute an avalanches running course. The model also predicts the variations of height, speed and concentration of snow particles in the avalanche, as well as the level of turbulence. Application of the model to the Maseguchi avalanche, which occurred in 1986 at Niigata, Japan, shows it can provide reasonable prediction of the running course, height and speed of an avalanche.

UPSTREAM AND DOWNSTREAM CONSISTENT DISTRIBUTED SNOWMELT RUNOFF MODEL INCLUDING RESERVOIR REGULATION

The purpose of this study is to develop a upstream and downstream consistent distributed snowmelt runoff model including reservoir regulation, and carry out runoff analysis in the Sagurikawa River basin, which includes a reservoir. It aims at realizing reservoir operation in consideration of the action of the water in a basin, and grasping the amount of water resources of study basin by using the upstream and downstream consistent distributed snowmelt runoff model including reservoir regulation. The delineation of channel network used by the distributed hydrological model was created, and the upstream and downstream consistent distributed snowmelt runoff model includes reservoir regulation was developed. In this model, since the whole basin can be taken into account, it is possible to take various dam managements into consideration.

VERIFICATION OF THE SCALE OF “THE YOKOTA-GIRE FLOOD” FROM THE VIEWPOINT OF CHARACTERISTICS OF RAINFALL OF HISTORICAL FLOODS IN THE SHINANO RIVER BASIN

This study is conducted as part of the study on estimation of the peak discharge of “the Yokota-Gire Flood” in July 1896, one of the historical floods in the Shinano River Basin. This study analyses relationship between rainfalls and discharges of relatively large floods since 1956 with well recorded rainfalls and flood discharges, and particularly compares the Yokota-Gire Flood with the flood in September 1982, in which the similar amount of rainfall was recorded despite the difference of the number of precipitation stations exists. Making clear the characteristics of hourly and spatial distribution of the rainfalls which caused large floods in the Shinano River Basin, not only helped to improve the accuracy of the peak discharge estimation of the Yokota-Gire Flood and to verify its validity, but also clarified the statistical positioning of the Yokota-Gire Flood through rainfall characteristics.

Measurement and Calculation of Flow Velocity under the Wave Motion around a Submerged Breakwater

Two methods to calculate the wave deformation around a breakwater, the boundary element method and mild-slope equation method, are currently available. Their abilityto predict the flow velocity field in the field, however, is not known. In this paper, a detailed measurement of flow velocity both around and inside a porous submerged breakwater is carried out in the laboratory wave flume and the result is compared with the analytical calculation.Experimental result shows amplification of flow velocity over the submerged breakwater and existence of complicated, though small, flow velocity inside the breakwater. For this flow structure, an unsteady mild- slope equation is formulated and the calculated flow velocity is shown to agree with the experimental data.

CRITICAL CONDITION FOR MOVEMENT OF SNOW CHUNKS IN AN OPEN CHANNEL

流雪溝における単一の雪塊の移動限界について理論的・実験的検討を行った. 理論では, 大きな雪塊に作用する流下方向の力の釣合から雪の移動限界を求めた. また, 理論との比較のため3種類の水路を用いて雪塊及び模擬雪塊を用いた実験を行った. この実験結果を理論値と比較したところ, 様々な雪質, 水路床勾配, 水路底面条件に対する実験結果が理論で説明できる事を示した.

A feasibility study of a system of urban snow removal and storage, integrated with air conditioning: Part II: Snow conveying and storage facilities and economy of the system.

集雪冷房システムの可能性を知るため, 第1報に引き続いて, 長岡市内の16km2の市街地を対象に, 集めた雪を送る雪水輸送システムと, 保存する貯雪施設の設計をした.また, 設計したシステムの能力と経済性の評価をした.結果を要約するとほ) このシステムは技術的に実現可能である.2) このシステムの排雪能力で対象地域の10~36%の面積が無雪化される.3) このシステムの冷房能力は, 地域内の住宅冷房を賄うことができて, 年間の電気エネルギーが40%削減できる.4) 建設費は1217億円と積算され, あらゆる意味で高価過ぎる。5) コストの大幅な低減をもたらす新技術の開発が, 今後の要点である.

A feasibility study of a system of urban snow removal and storage, integrated with air conditioning

集雪冷房システム (豪雪都市で冬に市街の雪を集め, 郊外の貯雪池に保存し, 夏に冷水を供給して建物を冷房するシステム) の可能性を知るため, 長岡市を対象として, システムの設計とその性能および経済性の評価を試みた.まず, このシステムの立地条件を調べ, 気象と地形などの都市の条件から, 長岡市が本システムに適した都市であることが分った.そこで長岡市の信濃川東岸の16km2の市街地を対象に, 5000t/hの能力を有する集雪システムを設計した.また, そこに5500台設置される大小の雪押込機を設計した.なお, ここで集められた雪の輸送システムと貯蔵施設の設計, さらに, 設計したシステムの性能と経済性の評価は第2報で述べた.