Browsing by Author "Stefan, Heinz G."

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All-Weather Ground Surface Temperature Simulation
(St. Anthony Falls Laboratory, 2006-09) Herb, William R.; Janke, Ben; Mohseni, Omid; Stefan, Heinz G.
Thermal pollution from urban runoff is considered to be a significant contributor to the degradation of coldwater ecosystems. Impervious surfaces (streets, parking lots and buildings) are characteristic of urban watersheds. A model for predicting temperature time series for dry and wet ground surfaces is described in this report. The model has been developed from basic principles. It is a portion of a larger project to develop a modeling tool to assess the impact of urban development on the temperature of coldwater streams. Heat transfer processes on impervious and pervious ground surfaces were investigated for both dry and wet weather periods. The principal goal of the effort was to formulate and test equations that quantify the heat fluxes across a ground surface before, during and after a rainfall event. These equations were combined with a numerical approximation of the 1-D unsteady heat diffusion equation to calculate temperature distributions in the ground beginning at the ground surface. Equations to predict the magnitude of the radiative, convective, conductive and evaporative heat fluxes at a dry or wet surface, using standard climate data as input, were developed. Plant canopies were included for surfaces covered by vegetation. The model can simulate the ground surface and subsurface temperatures continuously throughout a specified time period (e.g. a summer season) or for a single rainfall event. Ground temperatures have been successfully simulated for pavements, bare soil, short and tall grass, trees and two agricultural crops (corn and soybeans). The simulations were first run for different locations and different years as imposed by the availability of measured soil temperature and climate data. Data came from sites in Minnesota, Illinois and Vermont. To clarify the effect of different land uses on ground temperatures, the calibrated coefficients for each land use and the same soil coefficients were used to simulate surface temperatures for a single climate data set from St. Paul, MN (2004). Asphalt and concrete give the highest surface temperatures, as expected, while vegetated surfaces gave the lowest. Bare soil gives surface temperatures that lie between those for pavements and plant-covered surfaces. The soil temperature and moisture model appears to model surface temperatures of bare soil and pavement with RMSEs of 1 to 2°C, and surface temperatures of vegetation-covered surfaces with RMSEs of 1 to 3oC. The plant canopy model used in this study, based on the work of Best and Deardorff, provides an adequate approximation for the effect of vegetation on surface heat transfer, using only a few additional parameters compared to bare surfaces. While further simplifications of the model are possible, such simplifications do not reduce the number of required input parameters, and do not eliminate the need for estimating the seasonal variation of the vegetation density. A model for roof temperatures was also developed, based on the surface heat transfer formulations used for pavement. The model has been calibrated for both a commercial tar/gravel roof and a residential roof. Compared to pavement, the roof surface reach similarly high maximum temperatures, but reach lower minimum temperature at night cool due to their lower thermal mass.
Analysis and Simulation of Mixing of Stratified Layers or Reservoirs by Air Bubble Plumes
(St. Anthony Falls Hydraulic Laboratory, 1990-12) Zic, Kresimir; Stefan, Heinz G.
The goal of the research presented in this report is to analyze, understand, and simulate the flow field induced by a bubble plume in a lake or reservoir. This is useful and necessary for the design of lake or reservoir aeration and destratification projects. Three mathematical models were developed and laboratory experiments were performed. Experiments similar to the ones presented here are not available in the literature but were necessary to understand the governing physical processes and to verify the mathematical models. What makes these experiments unique, in comparison with other bubble plume measurements is the description of the entire flow field (not just the flow in vicinity of the bubble plume), the inclusion of stratified ambient water, and the evaluation of destrati:fication over time. The first. model developed is a modified version of a dynamic 1-D mathematical model originally formulated by Goossens[1979]. The improved model is based on the research described here and is linked to a general dynamic lake model MINLAKE. It is a tool useful for lake restoration projects, particularly for evaluation of different restoration techniques. The second model is also an integral model of a bubble plume. The flow field induced by an air bubble plume in stratified ambient water is presented in the general context of mixing mechanics of water jets and plumes. The third model is a 2-D numerical model that gives insight into the subregions of the flow field. The 2-D model solves the Reynolds' equations by using the buoyancy-extended version of the k-e model as a closure of the turbulent quantities. The effect of the bubbles in the fluid flow is modeled by imposing internal forces in the region where the air bubbles are present. A discussion of lake aeration as an oxygen transfer technique is beyond the scope of the research described herein.
Analysis of Flow Data from Miller Creek, Duluth, MN
(St. Anthony Falls Hydraulic Laboratory, 2008-11) Herb, William R.; Stefan, Heinz G.
This report summarizes an analysis of flow and precipitation data for Miller Creek, a trout stream in Duluth, MN, which was undertaken in support of the MPCA-mandated temperature TMDL. The main goals of this analysis were to determine the availability and quality of Miller Creek flow data and to characterize typical summer low flow conditions to be used in subsequent stream temperature analysis. Flow data from the three existing flow aging sites (lower, middle, upper) on Miller Creek were analyzed, along with precipitation data from the Duluth International Airport. The analyses of flow and precipitation data suggest that the flow data at the lower site are relatively consistent for all years, except 2007. Flow data from the middle site for the periods 1997-2003 and 2004-2007 have different character, with the 2004-2007 data from the middle site considered suspect. Flow data from the upper site (Kohl’s) in 1997 and 1998 appear reasonable, but a rating curve does not exist to translate stage data to flow for 2003 – 2007. Relationships between stream flows and precipitation have been established at weekly timescales and are reasonable (r2 = 0.70), but with RMSEs similar in magnitude to the mean flows. Based on 1997 and 1998 data, weekly-averaged flows at the middle and upper gaging sites are, on average, 92% and 77% of the lower site, respectively. This suggests that a large fraction of the flow in Miller Creek originates from the upper portion of the watershed, upstream of the Kohl’s site. A statistical analysis of five years of flow data from the Miller Creek lower site indicates that low flows in the range of 1 to 2 cfs are quite common at weekly time scales. Therefore a rainfall event of moderate magnitude may be expected to have a significant impact on stream flow and temperature at the lower site. Although the flow record is relatively short (5 years), the results of a frequency analysis suggest that weekly mean flows near zero are possible with a 10 year return period.
Analysis of Stream Temperature Data from Miller Creek, Duluth, MN
(St. Anthony Falls Laboratory, 2009-10) Herb, William R.; Stefan, Heinz G.
This report summarizes an analysis of stream temperature and associated climate data for Miller Creek, a trout stream in Duluth, MN. The study was undertaken in support of an MPCAmandated temperature TMDL. The main goals of the analysis were 1) to characterize the spatial and temporal variations of stream temperature and 2) to determine the main drivers of stream temperature exceedances in Miller Creek. Stream temperature and flow data from 1997-98, 2003-05, and 2007-08 were analyzed at hourly to annual time scales. Included were water temperature data from the main stem of Miller Creek, its tributaries, and from storm sewer outlets to Miller Creek. Stream temperature in Miller Creek was found to be highly correlated to air temperature from the Duluth Airport at daily to annual time scales. Temperature exceedances (T > 20 ºC) were found to be caused mainly by strong atmospheric heat transfer to the stream due to low channel shading in the middle reaches of Miller Creek. Only 5 to 10% of all temperature exceedances appear to be associated with surface runoff from rainfall events, and even fewer are associated solely with surface runoff. Little evidence was found that lower stream flow leads to increased stream temperature and more frequent temperature exceedances. In mid summer tributaries of Miller Creek are typically at a lower temperature than the main stem of Miller Creek. The tributary at Chambersburg Ave. appears to measurably lower the temperature of the main stem, up to several degrees Celsius. The roles of groundwater and wetlands in the water (flow) and heat budgets of Miller Creek can not be quantified based on the available stream temperature records.
An Analytic Model for Runoff and Runoff Temperature from a Paved Surface
(St. Anthony Falls Laboratory, 2006-10) Herb, William R.; Janke, Ben; Mohseni, Omid; Stefan, Heinz G.
Existing simplified runoff models such as SCS synthetic hydrographs give some ability to predict surface runoff, but are generally developed for larger watersheds, and do not necessarily represent the actual variation in flow rate with varying precipitation rate. For the purposes of simulating runoff rate and runoff temperature from small parcels of land, a new runoff model was developed based on Manning’s equation. The runoff model is analytical and spatially integrated (zero-dimensional), in that flow depth, flow rate and runoff temperature are computed at one point, the outlet. By taking into account expected variations in the upstream flow depth, the model closely matches the simulations results of a 1D kinematic wave model. The analytic runoff model was coupled to a 1D soil temperature and moisture model, to enable simulation of infiltration, runoff rate and runoff temperature.
Annual Stream Runoff and Climate in Minnesota’s River Basins
(St. Anthony Falls Laboratory, 2010-09) Vandegrift, Todd R.; Stefan, Heinz G.
Stream flows recorded by the USGS from 1946 to 2005 at 42 gauging stations in the five major river basins of Minnesota and tributaries from neighboring states were analyzed and related to associated climate data. Goals of the study were (1) to determine the strength of the relationships between annual and seasonal runoff and climatic variables in these river basins, (2) to make comparisons between the river basins of Minnesota, and (3) to determine trends in stream flows over time. Climatic variables were air temperature, precipitation, the Palmer Drought Severity Index (PDSI), and the Palmer Hydrological Drought Index (PHDI); the latter are common indices of soil moisture. Water year averages showed stronger correlations than calendar year averages. Precipitation was a good predictor of stream flow, but the PDSI was the best predictor and slightly better than PHDI when linear regressions at the annual timescale were used. With an exponential regression PDSI gave a significantly better fit to runoff data than PHDI. Five-year running averages made precipitation almost as good a predictor of stream flow (runoff) as PDSI. A seasonal time scale analysis revealed a logical stronger dependence of stream flow on precipitation during summer and fall than during the winter and spring, but all relationships for seasonal averages were weaker than for annual (water year) averages. Dependence of stream runoff on PDSI did not vary significantly by season. On a monthly timescale the strength of correlation between precipitation and runoff dropped off significantly, while PDSI was still a decent predictor in all months but the spring. Annual stream flow in the Upper Mississippi River Basin, including the Minnesota River Basin, had the strongest dependence on precipitation and PDSI. The Red River of the North Basin showed lower than average dependence on precipitation and average dependence on PDSI. The Rainy River Basin and the Lake Superior Basin showed the weakest dependence of annual stream flow on precipitation and PDSI. The relationship between stream flow and precipitation can be expressed most easily by an annual average runoff coefficient, i.e. the ratio of runoff to precipitation in a year. Runoff coefficients vary significantly across the state of Minnesota, from more than 0.4 in the northeast to less than 0.1 in the northwest. Trends in runoff coefficients were estimated from averages for 20-year periods from 1926-1945 to 1986-2005, although data for 1926-1945 were sparse. According to our analysis, runoff coefficients in some of the major river basins of Minnesota have increased significantly during the last 40 years. The Lake Superior and Rainy River Basins have high and invariant characteristic runoff coefficients around 0.35. The Red River Basin has the lowest characteristic runoff coefficient at ~0.14 but its value has consistently increased from the beginning of the record. The Mississippi Headwaters Basin characteristic runoff coefficient has increased to ~0.24. The Minnesota River Basin runoff coefficient (from the Minnesota River at Jordan, MN station) has also increased significantly and consistently to 0.19. The largest increases in runoff coefficients were found in the Red River and the Minnesota River Basins, the two basins with the lowest runoff coefficients; runoff coefficients in some tributary or sub-watersheds have doubled. In the Lake Superior and Rainy River Basins, and in the St. Croix River watershed, little change in runoff coefficients was found. Overall runoff coefficients drop significantly from east to west in Minnesota. This distribution does not seem to have changed over time. Increases in runoff coefficients over time have been highest in the west, and lowest in the east of Minnesota. One can hypothesize that changes in stream flow in Minnesota’s west are mainly due to land use changes that have lead to faster and easier surface runoff from the land since the beginning of European settlement. An explanation based on climatological factors can, however, also be offered. Precipitation has increased in all of the river basins of Minnesota over the time period of 1926 to 2005, but the largest changes have occurred in the south and west and little change in the northeast of Minnesota. Changes in total annual runoff (in/yr) between 1946 - 1965 and 1986 – 2005 increased at 38 of 42 stream gaging stations analyzed. Only 4 gaging stations, 3 in the Lake Superior and Rainy River Basins showed decreases, with all being less than 3%. The largest increases in average annual runoff were at 19 gaging stations in the Red River and Minnesota River Basins; at 17 of these, increases were from 60% to 132%, and at the remaining two stations the increases were 19% and 20%. The southern Minnesota watersheds with the largest increases in runoff also had the largest increases in precipitation. Overall, stream flow, expresses as annual runoff (in/yr), has increased since the beginning of stream gaging in Minnesota and the Upper Midwest, although periods of substantially lowered stream flows have occurred, e.g. in the drought period of the 1930s. Not only has the runoff (cm/yr) increased, but runoff coefficients, i.e. the ratio of runoff to precipitation, have also increased. When viewed as a percent change of annual runoff, the largest stream flow changes have occurred in the western part and the lowest in the eastern part of Minnesota. Increases in absolute values of annual runoff, percent of runoff, and runoff coefficients have been quantified in this study.
Baseflow Analysis of the Upper Vermillion River, Dakota County, Minnesota
(St. Anthony Falls Laboratory, 2008-06) Erickson, Timothy O.; Stefan, Heinz G.
Estimates of groundwater recharge are important for water resources planning and management, e.g. to determine the sustainability of groundwater resources. Estimates of groundwater recharge can be obtained by streamflow, especially baseflow, analysis. The Vermillion River, located at the southern fringe of the Minneapolis-St. Paul Metropolitan Area, is a DNR-designated groundwater-fed trout stream. How the stream flow in the Vermillion River and its tributaries is affected by urban development encroaching into the watershed is a pressing question. The baseflow in the Upper Vermillion River was therefore analyzed to determine the river’s groundwater recharge and minimum flow potential. The study site watershed includes approximately 129 square miles of the 338 square miles of drainage area within Dakota and Scott Counties. Two methods, the baseflow-separation method and the recession-curve-displacement method, were applied to the streamflow data from the USGS stream gauging site #05435000 near Empire, MN, to estimate baseflow and groundwater recharge in the Upper Vermillion River. The USGS computer programs PART and RORA were used to perform the baseflow analysis. The results of the analysis were used in conjunction with a water budget to estimate other hydrologic variables in the Upper Vermillion River basin at the annual timescale. It was determined that about 24% of the average annual precipitation reaches the stream as either baseflow or direct runoff. About 20% of the annual precipitation or approximately 80% of the annual streamflow in the Upper Vermillion River is baseflow from cold groundwater sources. The average annual estimates were found to compare well with results of previous studies (Baker et al. 1979, Ruhl et al. 2002, Lorenz and Delin 2007).
Buoyancy Induced Plunging Flow Into Reservoirs and Costal Regions
(1986-07) Farrell, Gerard J.; Stefan, Heinz G.
The water in a river flowing into a reservoir, lake or coastal region is rarely of exactly the same density as the ambient water in the waterbody. The density difference may be due to a difference in temperature or in concentration of dissolved or suspended substances. Small density differences can have dramatic effects on the flow patterns that develop in the waterbody. In particular, when the river water is denser than the ambient, I the incoming flow dips beneath the ambient water and flows along the reservoir bottom or beach as a density current. Such flows are termed plunging flows. Figure 1-1 shows a plunging flow situation over a sloping bottom with various aspects of the flow illustrated. The position on the water surface where the flow actually plunges is known as the plunge point or plunge line. It will frequently be delineated by a collection of floating debris held by the reverse current generated in the ambient water by the plunged flow. After plunging, the flow becomes a density current underflow. The dynamics of such currents are reasonably well understood [Ellison and Turner, 1959]. The region surrounding the plunge point and encompassing the transition region between the river inflow and the density current is termed the plunge region. This region can be characterized by its location in the reservoir, as expressed in the case illustrated by the depth at the plunge line H ,and by the amount of mixing that occurs in the region between the inflow and ambient waters. A study of flow in the plunge region with particular reference to these two characteristics forms the subject matter of this report. An understanding of the plunging phenomenon is important from the point of view of water quality modelling, reservoir sedimentation studies, and effluent mixing analyses. Ford and Johnson [1983] review a number of cases in which plunging flow had large water quality implications. The hydraulics of reservoir sedimentation are reviewed by Graf [1983a, b]. Stefan et a1. [1984] describe some effects of plunging on effluent mixing characteristics.
Calibration of the Monthly Time Scale Runoff Model
(St. Anthony Falls Laboratory, 1996-11) Mohseni, Omid; Stefan, Heinz G.
The stream runoff model developed by Mohseni and Stefan (1996) has a monthly time scale and is based on the water budget theory. Its function is to make mean monthly runoff projections under different climate scenarios. The model uses 6 climate variables, 11 watershed and soil parameters, and 3 parameters related to both climate and runoff. Some of the parameters are measurable and, therefore, obtainable as model input. The model lumps all watershed and soil parameters both vertically and horizontally. A nonsystematic calibration procedure gives different results, depending on the initial values chosen for some of the calibration parameters. The calibration parameters of the model are related to the two processes which are the most difficult to quantity and where the most information is required: direct runoff and snowmelt runoff. A systematic calibration procedure has been added to the original model to avoid inconsistencies in the results. The systematic calibration procedure is selected for the direct runoff parameters. For the snowmelt runoff, only some modifications in input are implemented. Base flow algorithm also required some changes in estimating the hydraulic conductivity of the storage below the root zone in order to better fit the water budget theory and Darcy's Law. For testing, the modified model is applied to two watersheds in two different climate regions, one in northern Minnesota and one in southwestern Oklahoma.
Cavity Formation and Associated Drag in a Supercavitating Flow Over Wedges in a Boundary Layer
(St. Anthony Falls Hydraulic Laboratory, 1964-04) Stefan, Heinz G.; Anderson, Alvin G.
Supercavitating flow over wedges (half-wedges) attached to a solid boundary can be simulated by air injection in the wake of the wedges. Information on cavity formation behind single wedges in a boundary layer, specifically, cavity length, air demand, and pressure distribution inside and outside the cavity as a function of wedge characteristics (height and angle), stream velocity, and blockage effect was obtained by experiment. Drag on such single artificially supercavitating wedges was measured. Experiments were carried out in a conduit of rectangular cross section with the wedges attached to the bottom. The ultimate purpose of the investigation was to examine whether a cavity generated on a flat plate has a skin friction reducing effect and how such a cavity can be generated most efficiently by a wedge without introducing important supplementary drag.
Certain Computational Aspects of Modeling Stratified Environmental/Geophysical Flows Pertaining to Lakes
(St. Anthony Falls Laboratory, 2000-03) Stefanovic, Dragoslav L.; Stefan, Heinz G.
Two intricate issues reiated to environmental hydrodynamics and water quality numerical modeling, with specific application to lakes, are addressed in this report: turbulent closure for stratified flows and transformation of the physical domain into a computational domain. Both problems are very important for the development of an accurate and efficient numerical algorithm intended to simulate thermo-hydrodynamics and transport processes in a lake (pond) cross section. The first section of the report considers the state-of-the art in turbulence modeling of environmental/geophysical flows (e.g. lakes, oceans, atmosphere) particularly in stratified ambiences, where the vertical turbulent transport is significantly hIndered by density stratification. The findings and recommendations stemming from this investigation are reported herein. In the second section of the report, the numerical treatment of irregular lake geometry is described in detail and a simple, efficient mapping transformation is proposed to facilitate the computation in a lake cross section of an arbitrary form.
Characteristics of Minnesota's Cisco Lakes
(St. Anthony Falls Laboratory, 2009-04) Fang, Xing; Alam, Shoeb R.; Jacobson, Peter; Pereira, Don; Stefan, Heinz G.
Bathymetric and other limnological characteristics of 620 Minnesota cisco lakes have been analyzed and compared with the same characteristics in another Minnesota lakes database consisting of 3002 lakes. It has been found that, on average, Minnesota cisco lakes are deeper, more transparent and less trophic than other lakes. They are preferentially located in north central and northeastern Minnesota.
Climate Change Effects on Water Temperature and Dissolved Oxygen in Five North Carolina Lakes
(St. Anthony Falls Laboratory, 1996-07) Rasmussen, Anders H.; Stefan, Heinz G.
A deterministic, year-round, one-dimensional water quality model, MINLAKE95, was used to investigate climate change effects on water temperatures and dissolved oxygen (DO) in five North Carolina lakes. The model was applied in daily timesteps over periods of several years. Past (recorded) weather conditions and a projected climate scenario under a doubling of atmospheric carhon dioxide were used as model inputs. Many of the lakes in the southeastern United States are matl~made reservoirs. Three such reservoirs atld two shallow natural lakes were modeled. The reservoirs are in the Piedmont and Mountain regions of North Carolina and are from 20 m to 65 m deep. The natural lakes are in the Coastal Plain and less than 4 m deep. All five lakes are major water bodies with long hydraulic residence times and surface areas ranging from 11 to 58 km2• Standard errors of simulation relative to point measurements were 2.0DC for water temperature and 1.4 mg L-J for dissolved oxygen. Measurements were available as profiles against depth at a single station in each lake. Each lake was modeled under past lxC02 climate conditions (1961- 79) and under a projected 2xC02 climate scenario. To illustrate the climate change effect, plots of isotherms and DO-isopleths in a depth versus time coordinate system were prepared. Mean annual and extreme year values were - plotted. To quantify the climate change effect further, extreme values of temperature and DO values in the surface layer and the bottom layer of each lake were tabulated, as well as periods of anoxia, lake volumes affected by anoxia, and periods and lake volumes with DO < 2' mg/l or DO < 3 mg/I. The .climate change effects were most apparent in maximum surface temperature increases of 2.8 to 3 DC, maximum bottom temperature increases of 1.6 to 2.9DC, and a 20% increase in evaporation in all five lakes. Low DO levels in the three reservoir hypolimnia were projected to be extended by up to 48 days in the 2xC02 climate scenario. Implications for fish habitat are that only the most temperature tolerant of the warm~water fishes would find suitable habitat in the natural 'lakes under the 2xC02 climate scenario. Cool~water fishes might survive at the intermediate (thermocline) depths of reservoirs where DO levels are sufficient and maximunl temperatures tolerable. Cold-water fishes would not find suitable habitat, except in refugia, e.g. due to groundwater inflows.
Continental-Scale Projections of Potential Climate Cbange Effects on Small Lakes in the Contiguous U .8. Vol. 2 Effects of Projected Future Climate Conditions on Lake Water Temperatures and Dissolved Oxygen
(St. Anthony Falls Laboratory, 1997-07) Fang, Xing; Ravindranath, Pasapula; Stefan, Heinz G.
This study is concerned with projections of climate change effects on lakes, especially small lakes with surface areas up to 10 km2 and depths up to '24m in the cold regions of the contiguous U.S. For this study, we have chosen lake parameters which are most directly influenced by climate and which in tum have much influence on aquatic lifeforms, water quality and water uses. The two main parameters studied herein are lake water temperature (T) and dissolved oxygen (DO) concentration. In the process, we have also obtained projections on evaporative water losses from lakes, ice covers on lakes and sediment temperatures below lakes. Potential changes of fish habitat (as constrained by T and DO) in lakes have also been estimated. To make such a broad study, we had to develop and apply process-oriented, simulation models which link atmospheric conditions to lake water conditions. Before the models were applied at the continental-scale in this report, the model formulations and assumptions were reviewed to examine what geographically variable parameters had to be introduced. The models were used on 27 different types of lakes. The lakes' chosen differed by surface area, maximum depth and transparency as measured by Secchi depth. These three parameters are known to have a crucial influence on lake water temperatures and DO concentrations. The Secchi depth was related to transparency as well as trophic state of a lake. This is a major assumption which will not hold true in lakes which show turbidity from inorganic suspended sediments. Secchi depth was related to mean annual phytoplankton chlorophyll-a concentration in a lake. This made it possible to estimate photosynthetic oxygen production without specification of nutrient inputs from the watershed. Lakes were also treated as having constant volume and long hydraulic residence times.
Continental-Scale Projections of Potential Climate Change Effects on Small Lakes in the Contiguous U.S. Vol. 3 Effects of Climate Conditions on Fish Habitat
(St. Anthony Falls Laboratory, 1998-12) Fang, Xing; Alam, Shoeb R.; Stefan, Heinz G.
This study is concerned with the projection of climate change effects on lakes, especially small lakes with surface areas up to 10 kttr and depths up to 24 m in the cold regions of the contiguous U.s. In this study, we have chosen lake parameters which are most directly influenced by climate and which in turn have much influence on aquatic lifeforms, water quality and water uses. The first two parameters studied were lake water temperature (T) and dissolved oxygen (DO) concentration. They have been estimated for past (1961-1979) climate conditions (Vol. 1 of this report) and a projected 2xC02 climate scenario (Vol. 2). Subsequently fish habitat in lakes, as constrained by T and DO, has been studied herein. In this Volume 3 of the report, water temperature and DO criteria (limits) of survival and good-growth of three fish assemblages (cold-water, cool-water, and warmwater), and parameters that quantify fish habitat in lakes in response to T and DO limits are given. Fish habitat was simulated in 27 types of lakes at 209 geographic locations over the contiguous U.S. under different climate scenarios. It includes a. validation of fish habitat simulations against fish observations and a sensitivity analysisof simulated winter fish habitat to three DO survival limits.
Cooling Water Intake Model Study For Nsp's Sherco Unit 3 Electric Power Generating Plant
(St. Anthony Falls Hydraulic Laboratory, 1985-12) Stefan, Heinz G.; Voigt, Richard L.; Lennington, James C.; Wetzel, Joseph M.; Bintz, David W.
Sherco Unit 3 is a coal-fired electric power generation facility under construction for Northern States Power Company (NSP), Minneapolis, Minnesota. It is located near the town of Becker, Minnesota, on the Mississippi River approximately 40 miles northwest of Minneapolis. Upon completion, it will join Sherco Units 1 & 2, which have been on-line since the mid 1970's (Fig. l-l). For condenser cooling, the plant uses a closed cycle cooling water system with forced draft wet cooling towers. To compensate for water losses from evaporation and releases' to the Mississippi River, an intake structure with two pumps of 15,000 gpm capacity each is located on the Mississippi River. With the addition of Unit 3, it became necessary to increase the water withdrawal capacity of the system. All three units will share the existing river intake facility.
Cooling-induced Convective Littoral Currents in Lakes: Simulation and Analysis
(St. Anthony Falls Hydraulic Laboratory, 1988-11) Horsch, Georgios M.; Stefan, Heinz G.
Cooling of lakes through the water surface at a constant per unit area rate causes, under calm conditions, the development of a horizontal temperature gradient along the littoral slope, since water columns of different depths have different rates of temperature change. The temperature gradient gives rise to a convective circulation that consists of a cool undercurrent and an unstable surface return flow. This thermally induced circulation initiates water exchange between the littoral and pelagic regions with potential for transport of dissolved constituents, thereby affecting the water quality of the lake.
Correlations Between Climate and Streamflow in the Little Washita River Watershed, OK
(St. Anthony Falls Laboratory, 1996-04) Kletti, Laura L.; Stefan, Heinz G.
Three substantially different methods have been used to relate the runoff in the Little Washita River, OK, to climate parameters. One method uses a detailed watershed runoff model SWAT, which integrates several well established hydrologic runoff model components. The second approach is based on a mean monthly water budget and calculates runoff as one of its components. The third approach simply correlates measured runoff with measured weather parameters. The timescales of these tlrree methods are substantially different: daily, monthly, and seasonal (3-months) for the three methods, respectively. The timescale is the shortest for the most process oriented model and the longest for the purely statistical method. The simplest of these three methods in terms of data requirement and computational effort is described herein and applied to the Little Washita Watershed. The other two are explained in reports by Mohseni and Stefan (1996) and Hanratty (1996).
Correlations of Minnesota Stream Water Temperatures with Air Temperatures
(St. Anthony Falls Laboratory, 1995-12) Pilgrim, John M.; Fang, Xing; Stefan, Heinz G.
Air temperatures are sometimes used as substitutes for stream temperatures. To examine the errors associated with this substitution, linear relationships between 43 Minnesota stream water temperature records and associated air temperature records were analyzed. Weather monitoring stations were, on average, 23.3 miles from the stream stations. From the lumped data set (38,082 data pairs), the general equations, Tw=4.4+0.81Ta, Tw= 1. 9+0. 97 Ta., Tw=0.7+1.04Ta, and Tw=3.3+0.89Ta ,with temperatures in °e, were derived for daily, weekly, monthly, and yearly mean temperatures, respectively. Standard deviations between all measured and predicted water temperatures were 3.soe (daily), 2.6°e (weekly), 1.9°e (monthly), and 1.3°e (yearly). Separate analyses for each specific stream gave lower standard deviations. The measured water temperatures follow the annual air temperature cycle closely. No time lags were taken into account, and periods of ice cover were excluded from the analysis.
Correlations of Oklahoma Stream Temperatures with Air Temperatures
(St. Anthony Falls Laboratory, 1996-10) Erickson, Troy R.; Stefan, Heinz G.
Air temperatures are sometimes used as substitutes for stream temperatures. To examine the errors associated with this substitution, linear relationships between 38 Oklahoma stream water temperature records and associated air temperature records were analyzed. Weather monitoring stations were, on average, 53.5 miles from the stream stations. From the lumped data set (38,859 data pairs), the general equations, Tw=O.787Ta+5.49, Tw=O.829Ta+4.67, and Tw=O.898Ta+3.47, with temperatures in degrees Celsius, were derived for daily, weekly, and monthly mean stream temperatures Tw, respectively. Mean yearly stream temperatures were also used, but the results proved to be inconclusive. Standard errors of prediction between all measured and predicted stream water temperatures in Oklahoma were 3.22DC (daily), 2.66DC (weekly), and 2.06DC (monthly). Separate analyses for individual stream gaging stations gave lower standard errors of prediction. The measured water temperatures follow the annual air temperature cycle closely. No time lags were taken into account, and periods of air temperatures below ODC were excluded from the analysis. The model is used to project water temperature increases in response to air temperature increases which may occur if climate changes due to a doubling of atmospheric carbon dioxide.

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