Topographic effects on the thermal structure of Himalayan glacial lakes : Observations and numerical simulation of wind

The thermal structure of two Himalayan glacial lakes, Tsho Rolpa and Imja in the eastern Nepal, was examined by observations in the pre-monsoon seasons of 1996 and 1997. Tsho Rolpa had an isothermal mixed layer at water depths of 0–20 m, whereas Imja did not possess such an isothermal layer. This difference in the thermal structure is explained by the condition that diurnal valley winds, producing wind-driven currents, blow strongly near the water surface of Tsho Rolpa, but very weakly near that of Imja. The wind observations above or near the end moraine indicated that a daily wind system of strong, diurnal valley winds and weak, nocturnal mountain winds is common to the lakes. It was suggested that with respect to the valley winds, the weak winds near the surface of Imja result from topographic screening effects of the upwind dead-ice zone and end moraine 20–25 m higher than the water surface. In order to ascertain the topographic effects, three-dimensional numerical simulation of airflow was carried out by making topographic models of actual size in the calculation domain, corresponding to Tsho Rolpa and Imja and their surrounding topography. The simulation revealed that, when winds blow at constant velocities of 1–5 m s−1 at 2 m above the points corresponding to the weather stations, the wind velocity at 2 m above the water surface for Imja is 33–42% smaller than for Tsho Rolpa. With increasing heights of the end moraine and dead-ice zone, the wind velocity near the lake surface efficiently decreased by decreasing the lake length from 3.1 or 2.2 km to 1.2 km

Water and Sediment Discharges from a Glacier-covered Basin under Maritime Climate in Kamchatka Peninsula, Russia

In order to clarify the characteristics of water and sediment discharges from glacier-covered basins under maritime climate, hydrological observations were carried out within a drainage basin which contains Koryto Glacier in Kamchatka Peninsula, Russia. Water discharge of a proglacial stream near the glacier terminus varied between 3 and 12 m^3 s^[-1] during the summer of 2000. Variation in suspended sediment concentration was positively correlated with water discharge, and values of sediment concentration ranged from 1.0 to 0.1 g1^[-1]. A runoff model which consists of two linear reservoirs in series was applied to the basin for simulating discharge variation. Considering a seasonal change in glacier drainage systems, this model can simulate stream discharge well. Three different models based on rating curve, multiple regression and sediment storage for suspended sediment transport estimation yield the total suspended sediment load during the observation period to be 10 × 10^6 kg. The sediment storage model assuming a reservoir beneath the glacier could bring the best estimate of variation in suspended sediment load. However, the multiple regression model gives a reasonable result and is also applicable for prediction.International Symposium on "Dawn of a New Natural History - Integration of Geoscience and Biodiversity Studies". 5-6 March 2004. Sapporo, Japan

Impact of Groundwater Level Decrease and Sea Level Fluctuations on Potential Saltwater Intrusion in the Subsurface Coastal Area of West Hokkaido, Japan

In order to limit possible inland seawater intrusion, important freshwater resources contained in coastal aquifers should be exploited carefully. Salinization of coastal waters is often due to inflow of dense saline water from the sea or deep inland geological layers, during heavy groundwater withdrawals, drought or long-term sea level rise. A continuous trend in the decrease of groundwater level and land subsidence, resulting from freshwater over-pumping, has been noticed in the subsurface of Hokkaido's coastal area facing the Sea of Japan, since the 1960's. This could lead to the decline of groundwater quality. This decline may be further amplified by seawater level increase. Past sea level records along this coast have shown continuous oscillations over various timescales of years and decades. A particularly high rate of sea level increase (3.2 mm/year) compared to the rise of the world ocean level, has been observed towards the northern edge of this coast. To avoid inland saltwater encroachment causing salt contamination of coastal aquifers, it's vital to determine the position of the seawater-freshwater interface and control its movement. For this purpose, water chemical analyses from drilled wells as well as analytical and numerical simulations are often employed to approximate the location of this boundary and understand the relevant processes that cause saltwater intrusion in coastal aquifers. For the present study, two modeling solutions are used to determine the shape and position of the interface between the landward potential seawater intrusion and subsurface freshwater outflow to the coast. Then, investigations are conducted to examine the impact of groundwater level decrease and sea level fluctuations, on the extent of this saltwater interference in the dynamics of the coastal flow system of the area.International Symposium on "Dawn of a New Natural History - Integration of Geoscience and Biodiversity Studies". 5-6 March 2004. Sapporo, Japan

Environmental factors controlling stream water temperature in a forest catchment

Heat budget of a stream, the Putoisaroma Stream, Hokkaido, Japan, in a forest catchment was estimated in order to investigate environmental factors controlling stream water temperature. In August 2008–October 2009, water temperature was measured at six sites along the stream channels, and the streambed temperature was measured at depths of 5 cm and 30 cm at one of the sites. In order to quantify incoming and outgoing radiations at the stream surface, hemispherical photographs were taken and the shading factors (ratio of the shade to the whole sky) were calculated at the observation sites over the summer. The shading factors, exhibiting seasonal and spatial variations, produced seasonal and spatial changes of shortwave and longwave radiations. The wind speed above stream surface was much smaller than in an open field, which produced turbulent heat fluxes one third as large as that in the open field. The shortwave and longwave radiations and the advective heat flux from upstream showed the major contribution to the stream heat budget, while the streambed heat conduction was secondary. The time series of stream water temperature were simulated well (RMSE = 0.771 ℃, NASH = 0.888) by applying the estimated heat budget. This evidences that the quantification of the shade above stream surface and the calculation of the heat budget are both reasonable. The sensitivity analysis for the simulation indicates that the shading factors along the stream channels control the stream water temperature

Geothermal heat flux into deep caldera lakes Shikotsu, Kuttara, Tazawa and Towada

Geothermal heat fluxes into the deepest waters of four caldera lakes were measured. Temperature profiles within the stratification period between July and November 2007 allowed a quantification of the acquired heat. Due to their enormous depth, heat input from the lake bed was locally separated from heat fluxes at the surface. In conclusion, a direct measurement of geothermal heat input could be accomplished. Although enhanced geothermal activity could be suspected in all cases, two lakes showed a geothermal heat flux of 0.29 or 0.27 W/m(2) (Lake Shikotsu and Lake Tazawa), as found in other regions not affected by volcanism, while both other lakes (Lake Kuttara and Lake Towada) showed a greatly enhanced heat input of 1 or 18.6 W/m(2), respectively. In conclusion, within our investigated set, all lakes acquired more heat from the underground than the continental heat flux average. Hence, the heat flux into the lakes from the ground was not dominated by the temperature gradient implied by the inner heat of the earth. Other effects like the general temperature difference of deep lake water and the groundwater or local sources of heat in the underground deliver more important contributions. Obviously the flow of water in the underground can play a decisive role in the heat transport into the deep waters of lakes

Subglacial drainage system changes of the Gulkana Glacier, Alaska: discharge and sediment load observations and modelling

Hydrological characteristics of englacial and subglacial drainage systems in Gulkana Glacier, Alaska, were examined by analysing temporal variations of discharge and sediment load in the proglacial Phelan Creek in 2001. From data plots on semi-log paper, it appeared appropriate to separate both discharge and sediment load into fast and slow components. The two components were possibly produced by two different drainage systems: an englacial and subglacial, “channellized” system in the ablation zone, and a subglacial, “distributed” system in the accumulation zone. The data indicate the occurrence of an event during which part of the “distributed” drainage system changed into the “channellized” drainage system. The daily time-series of discharge and sediment load were represented using a tank model. In the model, the drainage from an additional tank was added, supposing that a subglacial reservoir full of water and sediment collapsed slowly when the subglacial drainage system changed from distributed to channellized. The simulation with the collapsed tank gave much more reasonable results than those with no collapsed tank. The contribution of the collapsed tank to total sediment load is 24%, which is much larger than 9% to total discharge. Copyright © 2006 John Wiley & Sons, Ltd

A Study on the Blue Coloration of Ao-ike Pond, Aomori Prefecture, Japan: Formulation of a Physical Model in Terms of Radiance and Image Analyses

The blue coloration model of a closed pond, Ao-ike Pond, Aomori Prefecture, Japan, was formulated in terms of radiance by applying a theory of observation devices proposed by Szirmay-Kalos (2008) and Hanaishi’s reverse ray tracing method. In this model, three potential contributions to the coloration were considered; irregular reflection at the Lambertian pond bottom, density fluctuation scattering by water, and Mie scattering by suspended solids. By utilizing model formulas for these mechanisms, some parameters were determined in order to duplicate the images of the pond surface without solar shading by tree leaves above the pond surface, in addition to the images with sunbeam trajectories by solar radiations passing through tree leaves, which are emitted from the water and visible on the surface. Simulating the pictures of the pond surface and the sun-beam-image analyses revealed that the blue colorations of Ao-ike Pond are mainly produced (1) by the density fluctuation scattering of water itself and the white Mie scattering by suspended solids and (2) by the red-light absorption by water in the optical paths before and after the two scatterings. Then, the density fluctuation scattering of water and the Mie scattering by suspended solids exhibited contributions of almost equal magnitude. The contribution of irregular reflections at the pond bottom was judged to be relatively small