Browsing by Author "Mohseni, Omid"

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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.
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
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.
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.
Application of a Runoff Temperature Model (MINUHET) to a Residential Development in Plymouth, MN
(St. Anthony Falls Laboratory, 2007-06) Janke, Ben; Herb, William; Mohseni, Omid; Stefan, Heinz
The MINUHET (MINnesota Urban Heat Export Tool) model is a simulation tool used to route heat and storm water through a sub-watershed for a rainfall event or events of interest. The model includes components for developed land uses, undeveloped or vegetated land uses, pervious and impervious open channels, storm sewer systems, and storm water ponds. As a case study, the model has been applied to a 12.5 acre housing development in Plymouth, MN. The process of identifying necessary data is outlined, as well as a general strategy for organizing the input data and setting up the model for this particular watershed. A catch basin at the outlet of the development was instrumented for flow and temperature, and data were collected at the site from August 25, 2005 to October 1, 2005. The model was run for three rainfall events, and a comparison was made between observed and simulated flow rate and flow temperature at the development outlet. Overall, the model performed well. The RMSE for flow was 42.0 L/s, 10.4 L/s, and 14.3 L/s for the three events respectively, and the corresponding RMSE in storm water runoff temperature was 1.6 °C, 1.2 °C, and 1.9 °C. Observed and simulated volumeaveraged mean runoff temperature differed by less than 1.5 ºC for all three events. Total volume of runoff was predicted with reasonable accuracy by the model, especially for the first two events. Heat export, which is a measure of the heat content of the runoff above a certain reference temperature (in this case 16.0 °C), was accurately predicted for the second and third events. The model was found to be highly sensitive to saturated hydraulic conductivity and rainfall temperature (dew point temperature): volume of runoff from the pervious areas varied considerably with changes in hydraulic conductivity, and runoff temperature often tended toward dew point temperature, especially in the absence of large atmospheric or ground heat fluxes (e.g., late at night or early in the morning). This suggests that special care should be taken in selection of soil properties, and that all climate data should be collected as near to the study site as possible to improve the accuracy of runoff temperature estimation.
Assessment and Recommendations for Operation of Standard Sumps as Best Management Practices for Stormwater Treatment (Volume 2)
(Minnesota Department of Transportation, 2012-05) McIntire, Kurtis D.; Howard, Adam; Mohseni, Omid; Gulliver, John S.
In order to improve the performance of standard sumps as a best management practice (BMP) in treating stormwater runoff, a baffle was designed to be installed as a retrofit in standard sumps. The retrofit is a porous baffle called "SAFL Baffle". The effect of the SAFL Baffle on the performance of the standard sumps was assessed by conducting laboratory tests on small scale as well as full scale straight flow-through standard sumps equipped with the baffle. In addition, a number of tests were conducted to determine the performance of standard sumps with the SAFL Baffle when the baffle is clogged with debris like trash and vegetation. Furthermore, the performance of two other configurations of the baffle was studied: (1) the SAFL Baffle in a sump with an outlet pipe 90 degrees to the inlet pipe, and (2) the SAFL Baffle in a sump with some water entering the sump through an overhead inlet grate. Standard sumps equipped with the SAFL Baffle were evaluated using two metrics: (1) How well the system captures sediment during low flow conditions (Removal Efficiency Testing), and (2) how well the system retains the previously captured sediment during high flow conditions (Washout Testing). The results of the tests showed that the SAFL Baffle dissipates the energy of water entering the sump and as a result, at low flow rates, it captures sediment better than a standard sump with no baffle. More importantly, at high flow rates, the washout of the previously captured sediment reduces to near zero.
Assessment and Recommendations for the Operation of Standard Sumps as Best Management Practice for Stormwater Treatment (Volume 1)
(Minnesota Department of Transportation, 2011-08) Mohseni, Omid
Standard sumps are installed in many urban and suburban storm sewer systems. They may qualify as a best management practice (BMP) to pre-treat stormwater runoff by removing suspended sediment from the water. However, no data exist on the effectiveness of sediment removal and maintenance requirements of the sumps. Such data could justify giving pollution prevention credits to transportation departments, municipalities, counties and other local governments for the use of standard sumps. The goals of this study were to (1) evaluate four configurations of a flow-though standard sump for sediment capture and washout; (2) design a simple retrofit for standard sumps to improve sediment capture and decrease washout; (3) develop a performance function estimating the efficiency of standard sumps in removing suspended sediments; (4) develop another function estimating the sediment washout in standard sumps. This volume of the final report (Volume 1) only focuses on the performance of standard sumps. The second volume of the final report will be on the design and performance of the retrofit for improving the sediment capture and lowering the washout rate.
Assessment and Recommendations for the Operation of Standard Sumps as Best Management Practices for Stormwater Treatment (Volume 2)
(Minnesota Department of Transportation, 2012-05) McIntire, Kurtis D.; Howard, Adam; Mohseni, Omid; Gulliver, John S.
In order to improve the performance of standard sumps as a best management practice (BMP) in treating stormwater runoff, a baffle was designed to be installed as a retrofit in standard sumps. The retrofit is a porous baffle called “SAFL Baffle”. The effect of the SAFL Baffle on the performance of standard sumps was assessed by conducting laboratory tests on small scale as well as full scale straight flow-through standard sumps equipped with the baffle. In addition, a number of tests were conducted to determine the performance of standard sumps with the SAFL Baffle when the baffle is clogged with debris like trash and vegetation. Furthermore, the performance of two other configurations of the baffle was studied: (1) the SAFL Baffle in a sump with an outlet pipe 90 degrees to the inlet pipe, and (2) the SAFL Baffle in a sump with some water entering the sump through an overhead inlet grate. Standard sumps equipped with the SAFL Baffle were evaluated using two metrics: (1) How well the system captures sediment during low flow conditions (Removal Efficiency Testing), and (2) how well the system retains the previously captured sediment during high flow conditions (Washout Testing). The results of the tests showed that the SAFL Baffle dissipates the energy of water entering the sump and as a result, at low flow rates, it captures sediment better than a standard sump with no baffle. More importantly, at high flow rates, the washout of the previously captured sediment reduces to near zero.
Assessment of Stormwater Best Management Practices
(University of Minnesota, 2008-04) Anderson, James L.; Asleson, Brooke C.; Baker, Lawrence A.; Erickson, Andrew J.; Gulliver, John S.; Hozalski, Raymond M.; Mohseni, Omid; Nieber, John L.; Riter, Trent; Weiss, Peter; Wilson, Bruce N.; Wilson, Matt A.; Gulliver, John S.; Anderson, James L.
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.
Design of an Aeration System to Enhance Trout Habitat in Holland Lake, MN
(St. Anthony Falls Laboratory, 2001-07) Mohseni, Omid; Graske, Greg; Donovan, Richard; Stone, Mark; Fleming, Ryan; Stefan, Heinz G.
Holland Lake, a small but deep mesotrophic lake in the Twin Cities Metropolitan Area, has been considered by the Minnesota Department of Natural Resources, Division of Fisheries, for stocking with brown trout. Holland Lake, with a surface area of 0.14 km2 (35 acres) and a maximum depth of about 18.8 m (61 ft) consists of two shallow bays covered with rooted macrophytes and a deep main basin. The deep basin is thennally suitable for brown trout. However, due to a high oxygen depletion rate in summer, the lake becomes anoxic below the surface mixed layer from late June to early July. The rate of oxygen depletion below the surface mixed layer, based on field measurements, was estimated to be about 0.47 mg/day·l. Field studies conducted in the summers of 1999 and 2000 indicated that only horizontal advection processes could explain the observed high dissolved oxygen (DO) depletion rates. Density currents transport low DO water with high BOD into the deep basin metalimnion. These currents from the shallow bays were attributed to the temperature regimes of the shallow bays and groundwater flow through the lake. To improve brown trout habitat in Holland Lake, an aeration system has been designed based on the observed sumnler conditions. The aeration system comprises two bubble curtains along the border of the shallow bays to enhance mixing in the shallow bays and one metalimnetic aerator in the deep basin. The bubble curtains deepen the surface mixed layer down to 4 m, and prevent the fomlation of density currents from the shallow bays into the deep basin.
The Effect of Record L.ength on a Nonlinear Regression Model for Weekly Stream Temperatures
(St. Anthony Falls Laboratory, 1998-07) Erickson, Troy R.; Mohseni, Omid; Stefan, Heinz G.
A four parameter, logistic stream temperature model using weekly air temperature as the predictor of weekly stream temperature was fitted by least squares regression to records varying in length from 12 to 32 years. The records were from four streams in Minnesota and three streams in Oklahoma. The purpose of the study was to test if stream temperature models formulated from 3-year samples were representative of stream temperature models developed from the seven, full-length records. This test was done because the model had previously been applied to 3-year records from 585 streams and associated weather stations in the US (Mohseni et aI., 1997). Each full-length record was divided into 3-year samples containing up to 156 weekly air temperature and stream temperature data. The logistic stream temperature model was then fitted to the 3~year samples, as well as the full~length records. The models formulated from the full~length records were assumed to represent the "true" weekly air temperature/stream temperature relationships or "population" relationships. F-tests were used to determine whether statistical similarity between the 3~year sample and the full~length models existed. The results showed that approximately 33% of the 3-year sample relationships were not statistically similar to their respective population models. Further analysis of the 3-year sample and population regression parameters revealed notable discrepancies, especially for the parameter representing upper bound stream temperature. Twenty-six of thirty-one 3-year samples produced estimates of this parameter less than their respective popUlation model. In addition, the 3-year sample estimates of upper bound stream temperature demonstrated a large variance. Nonlinear, least squares parameter estimates were found to be inherently biased. The bias of nonlinear regression parameters is reduced with increasing sample length. Three-year weekly air temperature and stream temperature records can not exhibit the natural variance found in longer records. Records of more than 3-year duration are therefore necessary for the consistent representation of long-term weekly air temperature/stream temperature relationships.
Estimates of Climate Change Effects on Monthly Stream Runoff Applications to Streams in Minnesota and Oklahoma
(St. Anthony Falls Laboratory, 1996-09) Mohseni, Omid; Stefan, Heinz G.
This study examines the relationship between runoff and climate in two small watersheds in the mid~continental U.S. A parametric runoff model is applied to two watersheds with substantially different climates. One watershed is in the north~central U.S. with cold climate, heavily timbered, with an annual precipitation of 768 nun, an annual runoff of 448 mm and mean annual temperature of 3.5 DC. The other is in the south-central U.S. with warm climate, mainly covered with pasture and agricultural crops, with ,an annual precipitation of 746 nun, an annual runoff of 49 mm and mean annual temperature of 15°C. The parametric runoff model has a monthly time scale and simulates the historical monthly runoff of these watersheds with an R2 of 0.95 (Mohseni and Stefan, 1996). In order to investigate the effects of potential climate change on runoff from the two watersheds the parametric runoff model was applied with past and projected 2xCO2 climate scenarios as input. The output of two General Circulation Models (GCMs) was used to specify the 2xC02 climate scenarios. One GCM comes from the Goddard Institute of Space Studies (GISS) and the other from the Canadian Climate Center (CCC). Unfortunately the two GCMs project different precipitation under the 2xC02 scenarios for the northern watershed and therefore the projected stream runoff is also not fully consistent. In the northern watershed more runoff is projected to occur in winter under a warmer climate and less runoff in spring. A 24% increase in annual precipitation, mainly occurring in fall, causes about 12% increase in annual runoff under the GISS 2xC02 climate scenario. Under the CCC 2xC02 climate scenario, virtually no increase in annual precipitation is predicted, and hence a 5% decrease in annual runoff is projected; also, the runoff distribution throughout the year is projected to change. For the southern watershed, the GISS and CCC 2xC02 climate scenarios are in agreement. A 6% increase in annual precipitation, mainly projected to occur in fall, results in a 6% increase in annual runoff according to the parametric runoff model. Runoff in the southern watershed is currently only a small fraction of precipitation (less than 7%), Depending on the season in which precipitation or surface air temperature increases, the change in runoff differs. An increase in spring precipitation can cause a significant increase in the direct runoff, whereas an increase in fall precipitation causes an increase in the base flow later in fall and winter. This study has shown that the runoff-precipitation relationship in warm and seasonally dry regions is very different from that in temperate to humid climate regions. Therefore, runoff responses to climate changes are also substantially different.
Estimation of an Upper Bound for Weekly Stream Temperatures
(St. Anthony Falls Laboratory, 1998-08) Erickson, Troy R.; Mohseni, Omid; Stefan, Heinz G.
A four parameter, logistic stream temperature model has been previously developed to describe the S-shaped, weekly stream temperature/air temperature relationship (Mohseni et al., 1998). The four model parameters, evaluated by nonlinear, least squares regression, have specific physical interpretations. However, the least squares estimate of the model parameter representing upper bound stream temperature has been found to have several deficiencies. The deficiencies associated with the nonlinear, least squares fitting method with respect to the estimate of upper bound stream temperature are frequent underestimation, highly variable estimation with respect to record length and an insensitivity to the actual trends occurring at the extreme upper end of the stream temperature/air tern perature relationship. Two alternate statistical methods were therefore considered for the estimation of upper bound stream temperature that focused exclusively on the uppennost stTeam temperatures: the standard deviate method and the frequency distribution method.
Estimation of Groundwater Inflow to the Vermillion River from Observations of Stream Flow and Stream Temperature
(St. Anthony Falls Laboratory, 2009-11) Janke, Ben; Herb, William R.; Mohseni, Omid; Stefan, Heinz G.
A model has been developed for estimation of groundwater inflow to a stream reach from observations of stream temperature, groundwater temperature, stream flow rate, and standard weather parameters. The purpose of this model is to provide an estimate of groundwater inflow rate for stream reaches where groundwater inflow is significant. This information is useful for management of fisheries and urban development in watersheds where stream temperature is a concern. In particular, the model was developed for use in the Vermillion River, which has designated trout stream reaches that may be impacted by development in the watershed. The model estimates groundwater inflow rate from a stream reach heat budget, which takes into account atmospheric heat flux, sediment-water heat exchange, and groundwater inflow. The model requires the following data as input: stream temperature at the upstream and downstream ends of the stream reach, stream flow at either end of the reach, standard weather data, and no significant tributaries or inflows between the ends of the reach. The model was applied to six reaches in the Vermillion River watershed. Estimated groundwater inflow rates showed considerable spatial and temporal variability, both seasonally and between the two years simulated (2006 and 2007). In North Creek, groundwater inflow rate was 0.45 to 1.30 cfs/mile in 2007; in the upper Vermillion River main stem for the same period estimated inflow rates ranged from 0.15 to 3.87 cfs/mile. In the middle Vermillion River main stem, estimated inflow rates were unnaturally large and more variable (0.39 to 11.1 cfs/mile); these estimates include significant tributary inflow, which is lumped with groundwater inflow in the model. This, along with the failure of the model for reaches or periods involving high stream flows, is the likely source of the over-predicted groundwater inflow values. Simulations for lower South Creek showed negligible groundwater inflow for 2006; results for lower South Branch were very typical of a groundwater-fed stream, with relatively constant groundwater inflow (around 1.0 cfs/mile) that fluctuated only slightly during periods of heavy rainfall. A comparison of predicted groundwater inflow rates throughout the watershed for both dry (baseflow) and high-flow conditions suggest the presence of shallow groundwater, particularly in the lower reaches of the watershed. The significant variability in groundwater inflow rate predicted by the model can be traced to a number of factors, including data quality and sensitivity of the model to groundwater temperatures, stream shading/sheltering, and especially to stream flow. An extensive sensitivity analysis of the model is presented in this report, as well as an analysis of available data, in particular, groundwater temperature. Limitations of the heat budget approach to modeling groundwater inflow rate are also discussed and criteria for application of the model are developed from the results of sensitivity analysis.
Estimation of Runoff Temperatures and Heat Export from Different Land and Water Surfaces
(St. Anthony Falls Laboratory, 2007-02) Herb, William R.; Janke, Ben; Mohseni, Omid; Stefan, Heinz G.
This report describes work to analyze runoff temperatures and runoff heat export rates for a variety of terrestrial land covers and aquatic surfaces. Surface runoff temperatures and heat export have been simulated for ten terrestrial covers, an unshaded wet detention pond, a lake/reservoir, and a vegetated pond. A continuous simulation was run from April 1 to October 31, yielding a total of about 280 precipitation events for six years (1998-2000, 2003-2005). Six years of 15-minute climate data from the weather station at the MnROAD facility in Albertville, MN, were used as model input. In general, the variation in average runoff temperatures from terrestrial land covers and open water surfaces was moderate, from 24.9 °C for concrete to 21.5 °C for a forest. Pavements, commercial rooftops, bare soil, wet detention ponds, and lakes/reservoirs were all found to give runoff temperatures high enough to significantly impact stream temperature. Vegetated surfaces gave substantially lower runoff temperature and heat export than paved surfaces. Runoff temperatures from bare soils were consistently higher than from vegetated surfaces, but lower than from pavements. Residential roofs gave, on average, low runoff temperatures, due to very low thermal mass, while commercial roofs gave high runoff temperatures in some cases. Large water bodies (lakes and reservoirs) generally give very high runoff temperatures, but the quantity of runoff is highly dependent on the water level prior to the storm event. Analysis of a vegetated pond indicates that shading from emergent vegetation can reduce runoff temperature up to 6°C compared to an unshaded pond.
Heat Export and Runoff Temperature Analysis for Rainfall Event Selection
(St. Anthony Falls Laboratory, 2007-04) Herb, William; Mohseni, Omid; Stefan, Heinz
Thermal pollution by surface runoff from urban areas can contribute to the degradation of coldwater ecosystems. The hydrothermal characteristics of surface runoff from rainfall are therefore of interest. Three hydrothermal parameters of surface runoff have been studied: runoff temperature (oC), heat flux (W/m2) and total heat export (J/m2). Heat fluxes were defined above a reference temperature of 20oC. The results can be used to identify storm events that have the potential for the largest heat export from a watershed and consequently the strongest thermal pollution of a receiving coldwater stream. In this study, records of rainfall events and weather data are used to estimate the three hydrothermal parameters by model simulation. The model for predicting rainfall runoff temperatures and rates from an impervious surface (parking lot) has been described in Project Report No. 484 from the St. Anthony Falls Laboratory, University of Minnesota (Herb et al 2006). The weather data came from the MnROAD test site in Albertville, MN, and from the SAMSON data set. Runoff temperatures and heat export were calculated for a 100x100m paved surface using 6 years of 15 minute weather data or 30 years of 1-hour weather data. The 6-year data set contained 280 rainfall events from April through October. The 280 values of the three hydrothermal parameters were related to basic rainfall event parameters such as total rainfall, duration, and rainfall temperature (dew point). Average runoff temperature was found to be well correlated to dew point temperature during the storm, and air temperature and solar radiation prior to the storm. 20 extreme values of the hydrothermal parameters were ranked and also related to basic rainfall parameters. Partial duration series of hydrothermal parameters were analyzed separately for frequency of occurrence (return periods).
Heating of Rainfall Runoff on Residential and Commercial Roofs
(St. Anthony Falls Laboratory, 2010-01) Janke, Ben; Mohseni, Omid; Herb, William R.; Stefan, Heinz G.
A common assumption in stream water temperature modeling is that rooftops of all types contribute very little heat to runoff from rainfall. In this report we examine the accuracy of this assumption (a) by analyzing temperature data which we recorded on a residential rooftop, a commercial rooftop, and a concrete driveway, and (b) by simulating temperature profiles within rooftops and pavements, and estimating heat transfer from these surfaces to rainfall runoff. Analysis of both wet‐ and dry‐weather temperature data which we recorded over periods of several months allowed us to conclude that a driveway has a far greater capacity for heat storage and release than a rooftop, although the commercial rooftop was able to store and release more heat than the residential rooftop. On sunny days and prior to rainfall, rooftops can reach higher temperatures than paved surfaces, but not much heat is stored, and roof temperatures drop rapidly as cloud cover increases with an approaching storm. Interestingly, weather events leading to the highest dew point (rainfall) and surface temperatures often occurred during late night or early morning hours, contrary to the expectation that the worst‐case runoff heating events would occur during daylight hours. The analysis conducted for three rainfall events showed that the heat export from the commercial rooftop was roughly three times that of the residential rooftop, but only 30%‐90% of the heat export from the concrete driveway. Potential heat export was significantly higher for the driveway than for either rooftop.
Heating of Rainfall Runoff on Residential and Commercial Roofs
(St. Anthony Falls Laboratory, 2010-01) Janke, Ben; Mohseni, Omid; Herb, William R.; Stefan, Heinz G.
A common assumption in stream water temperature modeling is that rooftops of all types contribute very little heat to runoff from rainfall. In this report we examine the accuracy of this assumption (a) by analyzing temperature data which we recorded on a residential rooftop, a commercial rooftop, and a concrete driveway, and (b) by simulating temperature profiles within rooftops and pavements, and estimating heat transfer from these surfaces to rainfall runoff. Analysis of both wet- and dry-weather temperature data which we recorded over periods of several months allowed us to conclude that a driveway has a far greater capacity for heat storage and release than a rooftop, although the commercial rooftop was able to store and release more heat than the residential rooftop. On sunny days and prior to rainfall, rooftops can reach higher temperatures than paved surfaces, but not much heat is stored, and roof temperatures drop rapidly as cloud cover increases with an approaching storm. Interestingly, weather events leading to the highest dew point (rainfall) and surface temperatures often occurred during late night or early morning hours, contrary to the expectation that the worst-case runoff heating events would occur during daylight hours. The analysis conducted for three rainfall events showed that the heat export from the commercial rooftop was roughly three times that of the residential rooftop, but only 30%-90% of the heat export from the concrete driveway. Potential heat export was significantly higher for the driveway than for either rooftop. In conclusion, the results of the data analysis and heat export simulations support the assumption that residential rooftops contribute very little heating to runoff from rainfall. Commercial rooftops may have a thermal impact on rainfall runoff because of their greater thermal storage capacity. An asphalt pavement, (road or driveway) is expected to have a greater thermal impact than a concrete pavement. Commercial rooftops in addition to asphalt and concrete pavements should be considered when the water temperatures of rainfall runoff from highly urbanized areas are estimated.
Hydraulic Model Study of the Stilling Basin with a Baffled Chute
(2006-08) Mohseni, Omid; Lueker, Matthew; Carlson, Luke
Hydrodynamic Separator Sediment Retention Testing
(St. Anthony Falls Laboratory, 2010-03) Saddoris, David A.; McIntire, Kurtis D.; Mohseni, Omid; Gulliver, John S.
Hydrodynamic separators are widely used in urban areas for removal of suspended sediments and floatables from stormwater due to limited land availability for the installation of above ground stormwater best management practices (BMPs). Hydrodynamic separators are often sized based on some relatively frequent storm events. However, during less frequent storm events, device design treatment rates are exceeded and previously captured sediments can be washed out of the device.

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