Now showing items 1-10 of 10

• #### A nested watershed study in the Kuparuk River basin, arctic Alaska: Streamflow, scaling, and drainage basin structure

The central hypothesis of this dissertation is that permafrost influences the form, function, and scaling of hydrologic and geomorphologic characteristics in the Kuparuk River basin in Northern Alaska. This problem was addressed using three approaches: field hydrologic studies, statistical scaling studies, and geomorphology studies using digital elevation models. Permafrost and snow exert significant controls on hydrologic processes in the Kuparuk River basin. Storm hydrographs show fast responses, long time lags, extended recessions, and high runoff/precipitation ratios. These features arise from the diminished storage capacity caused by permafrost. Summer storm flow compositions in the are dominated by old water, as is commonly observed in basins without permafrost. However, the thawing active layer imposes seasonal trends on storm flow composition and other streamflow characteristics. These seasonal trends are often masked by precipitation patterns. Significant differences exist in the spatial variability and scaling of streamflow between arctic and temperate basins. Streamflow in arctic basins is subject to simple scaling, whereas streamflow in temperate regions is subject to multiscaling. Since the variability of streamflow downstream results from the timing of storm hydrographs upstream, regional scaling differences may result from the differences in runoff generation mechanisms in basins with and without permafrost. Fractal analysis of channel networks, and the scaling of mass distribution suggest that channel networks in the Kuparuk River basin are underdeveloped. Hillslope water tracks convey water off slopes, but the organization of water tracks lacks universal characteristics of mass and energy distribution common to other rivers, and hence cannot be considered fluvial channels. However, the heads of water tracks are located where some theoretical models of channel initiation predict that channels should occur. A likely scenario is that a rudimentary channel network was formed soon after deglaciation, but was never allowed to develop into a mature network due to the limits that permafrost imposes on erosion. An encompassing conclusion is that the Kuparuk River basin is adjusted to arctic conditions in both form and function. Consequently, thermal changes to the existing permafrost condition may impose significant changes in the erosional development of channel networks and in the subsequent hydrologic response.
• #### An Elaboration Of Two Methods To Investigate Unfrozen Water Movement In A Snow-Soil Environment (Tdr, Instrumentation, Heat)

Hydrologic research of processes related to snow and to frozen soil have generally been regarded as separate entities. The unknowns involved in these fields were so numerous, that few attempted to examine snow-soil interactions. Better tools (mathematical models and field equipment) are needed to study unfrozen-water movement in snow-soil systems and to understand and test theories of water movement in frozen media. The overall thesis objective is to see if Anderson's snow model can be modified to include soil heat and mass transfer to provide good simulations of these processes in a snow-soil environment. The first part of this thesis deals with the elaboration of the time domain reflectometry method to continuously measure the unfrozen water content of soil and snow in the field. The continuous monitoring, over a one-year period, of unfrozen water content at different soil depths was successful. The application of the same method to snow, was quite promising, but requires the addition of snow density. The second part of the thesis deals with the application of an energy and mass balance model to a snow cover and soil. The snow model satisfactorily simulated snow cover density, snow water equivalent, snow depth, time of disappearance, snow temperature and snowmelt runoff for the one accumulation and two snowmelt periods. The boundary from the soil surface was lowered to a certain soil depth to include detailed processes of heat and mass transfer occurring in the soil. The output values of the new model were compared with the data of one snowmelt period. It was found that instead of modifying Anderson's snowmelt model, it would be better to develop an entirely new model that would have two unknowns in the soil and the snow and only two boundaries: the snow-air interface and the soil at a certain depth in the ground.
• #### Application Of Natural Channel Design Principles In Conversion Of A Multiple-Thread To Single-Thread Channel On An Alluvial Fan: Mccallum Creek, Alaska

McCallum Creek crosses the Trans Alaska Pipeline in the Central Alaska Range near Paxson, Alaska. It was converted from a braided channel on an alluvial fan to a stable single thread channel at the pipeline crossing. Objectives included controlling the position of the channel at the pipeline and minimizing aufeis accumulations through the converted reach. A natural channel design methodology was used, which involves determining the dimension, pattern, and profile of a stable reference reach for the associated valley type and stream type and emulating those characteristics in the design reach. A failure mode analysis was conducted. Mitigative measures were identified for each potential failure mode. The channel was lowered to reduce surface energy loss and associated aufeis accumulations. Performance was good during the 2000 and 2001 seasons. Aufeis accumulations have not recurred. Lessons learned are presented from this and several similar projects constructed along TAPS in 2000 and 2001. <p>
• #### Development of a spatially distributed model of Arctic thermal and hydrologic processes (MATH)

A process based, spatially distributed hydrologic model with the acronym MATH (Model of Arctic Thermal and Hydrologic Processes) is constructed to quantitatively simulate the energy and mass transfer processes and their interactions within arctic regions. The impetus for development of this model was the need to have spatially distributed soil moisture data for use in models of trace gas fluxes (carbon dioxide and methane) generated from the carbon-rich soils of this region. The model is applied against the data from the Imnavait watershed (2.2 $\rm km\sp2)$ and the Upper Kuparuk River basin (146 $\rm km\sp2)$ located on the North Slope of Alaska. Both point and spatially distributed data such as precipitation, radiation, air temperature, and other meteorological data have been used as model inputs. Based on the digital elevation data, one component of the model determines drainage area, channel networks, and the flow directions in a watershed that is divided into many triangular elements. Simulated physical processes include hydraulic routing of subsurface flow, overland flow and channel flow, evapotranspiration (ET), snow ablation, and active layer thawing and freezing. This hydrologic model simulates the dynamic interactions of each of these processes and can predict spatially distributed snowmelt, soil moisture, and ET over a watershed at each time step as well as discharge at any point(s) of interest along a channel. Modeled results of spatially distributed soil moisture content, discharge at gauging stations and other results yield very good agreement, both spatially and temporally, with independently derived data sets, such as Synthetic Aperture Radar (SAR) generated soil moisture data, field measurements of snow ablation, measured discharge data and water balance computations. The timing of simulated discharge results do not compare well to the measured data during snowmelt periods because the effect of snow damming on runoff generation is not considered in the model. It is concluded that this model can be used to simulate spatially distributed hydrologic processes within the arctic regions provided that suitable data sets for input are available. This physically based model also has the potential to be coupled with atmospheric and biochemical models.
• #### Fluvial and hillslope geomorphology of Hoseanna Creek Watershed, central Alaska

Hoseanna Creek Watershed is rapidly eroding and provides excellent opportunities to describe and quantify hillslope and fluvial processes in the subarctic and in discontinuous permafrost terrain. High landslide and badland densities occur due to asymmetric geologic structure and weakly consolidated lithologies. Late Quaternary regional glaciofluvial processes and tectonism have changed local base level at least 100 m, inducing headward incision through weak lithologies and yielding high rates of sediment production. Earthflows, translational blocks, rotational blocks, lateral spreads or complex landslide types form in coal-bearing formations in response to lateral corrasion of toes by avulsing streams or to undermining of foot areas by headward incising streams. Slides undergo episodic resurgent activity when new lithostatic or hydrostatic thresholds are reached. Average horizontal displacement rates of seven slides monitored between 8/85 and 9/88 ranged from 0.2 m/yr in rotational blocks to 48 m/yr in the earthflows. Although unique sliding mechanisms are not apparent, permafrost and subarctic climate generate delays or catalysts for failure atypical of warmer climates. Freezing/thawing fronts affect soil strength and permeability; break-up/freeze-up processes affect the timing of water supply to the slide mass and affect development of aufeis-related ground-water pore pressures. Aspectual and lithologic variations combine to yield three geohydrologic subbasin types which govern discharge ranges. Regressions were performed on multiple sets of sediment-discharge (Ts-Q) data. Regression variance (r$\sp2$) was found to have a maximum natural threshold indicative of intrinsic variability. Wide ranges in Q (0.001 to 2350 cfs) and Ts (0.005 to 1600 g/l) necessitated log-log scales and power functions. Each geohydrologic subbasin has a unique Ts-Q relationship termed here the mean sediment concentration potential Cp. Systematic differences in regression parameters indicate that variations in spatial conditions define Cp, while systematic changes in Ts-Q regression residuals R (termed here the maintenance rate R$\sp*$) describe the temporal variability of Ts through time with respect to Cp. 50-95% of the annual sediment load is transferred during less than 3% of the year. Erosion rate indexes were established from peak load estimates; Nenana Gravel basins are eroding 260 times faster than schistose basins and ten times coal-bearing basins.
• #### Solute redistribution during freezing of sands saturated with saline solution

Columns of saturated saline sands were frozen under hydrostatic conditions with constant surface and base temperatures. Nine freezing tests were conducted using a silica sand with a permeability of about 10$\sp{-11}$ m$\sp2$ and salinities that ranged from 1 to 100 ppt but were generally near 35 ppt. Surface temperatures were generally 3 to 5 $\sp\circ$C colder than the freezing temperature of the solution and base temperatures were generally 0.5$\sp\circ$C warmer. A 4 to 10 day long period preceded the onset of convection and redistribution of the solute. The increased freezing rate due to the solute, the effects of brine expulsion and a small amount of water movement independent of the salt were measured during this period. Movement of water to the column surface was not associated with either vapor transport or salt sieving. The interface between the solid and liquid was a vertically diffuse interface rather than a sharp ice-bonded interface. Convection of the pore fluid occurred throughout the entire column. Pore fluid velocities were estimated to be on the order of 0.1 to 03 $\rm{m\over day}$ and do not exceed 1.4 $\rm{m\over day}$. Convection consisted of pore fluid in one half of the column moving down and pore fluid in the other half moving up and was associated with radial asymmetries in salinity, water content and ice-bonding. The effects of convection could be measured in the salinity profiles, but not in profiles of water content or temperature. A stability analysis showed the unstable density gradient in the partially frozen region was not sufficient to lead to convection. It was tentatively concluded that convection resulted from dense brine in the partially frozen region overlying less dense brine in the thawed region. Methods for estimating the final salinity profiles were not satisfactory since the BPS theory could not be applied to the experimental results and a stability theory for the pore fluid could not be developed which matched the experimental results. Application of these results to field situations is limited because of the restricted horizontal and vertical length scales. However, solute redistribution by convection is probably limited to freezing soils with large solute concentrations and large permeabilities.
• #### Studies of Bagley Icefield during surge and Black Rapids Glacier, Alaska, using spaceborne SAR interferometry

This thesis presents studies of two temperate valley glaciers---Bering Glacier in the Chugach-St.Elias Mountains, South Central Alaska, and Black Rapids Glacier in the Alaska Range, Interior Alaska---using differential spaceborne radar interferometry. The first study was centered on the 1993--95 surge of Bering Glacier and the resultant ice dynamics on its accumulation area, the Bagley Icefield. The second study site was chosen for purposes of comparison of the interferometry results with conventional field measurements, particularly camera survey data and airborne laser altimetry. A comprehensive suite of software was written to interferometrically process synthetic aperture radar (SAR) data in order to derive estimates of surface elevation and surface velocity on these subject glaciers. In addition to these results, the data revealed unexpected but fairly common concentric rings called 'phase bull's-eyes', image features typically 0.5 to 4 km in diameter located over the central part of various glaciers. These bull's-eyes led to a hypothetical model in which they were interpreted to indicate transitory instances of high subglacial water pressure that locally lift the glacier from its bed by several centimeters. This model is associated with previous findings about the nature of glacier bed hydrology and glacier surging. In addition to the dynamical analysis presented herein, this work is submitted as a contribution to the ongoing development of spaceborne radar interferometry as a glaciological tool.
• #### The interdependence of the thermal and hydrologic processes of an Arctic watershed and their response to climatic change

The heat and mass transfer processes which comprise the thermal and hydrologic regimes were monitored continuously from March 1985 until September 1989 in a small watershed on the North Slope of Alaska. Through these intense measurements, a better understanding of the physical processes which determine the character of an arctic watershed have been developed. The state of the hydrologic regime is a product of the thermal regime. The hydrologic and thermal regimes interact to such an extent that neither can be fully understood without considering the other. The consequences of a manmade or environmentally induced alteration in the thermal regime can have dramatic and perhaps dire effects on the hydrologic regime and vice versa. The implications of global warming reach beyond warmer air temperatures, milder winters and longer summers. The potential effects of climatic warming on the hydrologic regime of an arctic watershed were explored with respect to physical changes in the active layer and the resultant changes in the components of the annual water balance and the nature of the hydrologic cycle. With the advent of climatic warming, the annual depth of thaw in the permafrost will increase, affecting the amount of soil moisture storage, the depth to the water table, even the shape of the runoff hydrograph. The gradual thawing of the active layer was simulated using TDHC, a finite element heat conduction model which incorporated phase change. The results of four possible scenarios of climatic warming were input into HBV, a hydrologic model to elucidate the effects on the hydrologic regime. The results indicate an earlier, but less intense spring melt event, greater evaporation, greater soil moisture storage, and a potential for severe moisture stress on current vegetation types in early summer unless the precipitation pattern changes.