Tirupati Bolisetti

Performance and implementation of low impact development – A review

Climate change, urbanization, and ecological concerns are all driving the need for new stormwater management strategies. The effects of urbanization are exaggerated by climate change and thus the development of innovative stormwater management techniques are necessary to mitigate these impacts. One emerging stormwater management philosophy is low impact development (LID). LID utilizes distributed stormwater controls (often green infrastructure) as well as green spaces and natural hydrologic features in order to bring the hydrology of urban catchments closer to pre-development conditions. The review provides a summary of the knowledge of LID as a stormwater management technique and climate change mitigation measure as well as the current state of research and implementation of this topic. In order to provide a better understanding of the extensive scope that should be considered for design of low impact developments, methods of optimization, modelling, monitoring and the performance of LID alternatives is covered. LID has been widely adopted and proven successful in many cases; however, there remains uncertainty of its benefits. This review brings together knowledge from many sources in order to provide an overview of LID and examine its performance and implementation.

Ground source heat pump systems: current status

Geothermal energy is critical to achieving more sustainable and environmentally friendly energy usage. Geothermal energy and the availability of the technology, Ground Source Heat Pump (GSHP) systems are becoming increasingly popular for heating and cooling of buildings. GSHP installations in different countries are increasing at a rate greater than 25–60%. The GSHPs produce near zero emissions rates of greenhouse gases (GHGs).

Experimental investigations of colloidal silica grouting in porous media.

This paper presents the results of an experimental investigation performed to understand the processes influencing the injection of colloidal silica grout into porous media. Based on the combined analysis of grout injection pressures and the visually observed grout distribution patterns, three major processes, gelation, shear, and viscous fingering, have been identified to occur during grout injection. The results demonstrate the dynamic interplay between grout viscosity variations and the resulting flow instabilities.

Automated Linear and Nonlinear Reservoir Approaches for Estimating Annual Base Flow

AbstractThree automated base flow separation techniques based on linear and nonlinear reservoir approaches are used to identify the seasonal variation of base flow and to quantify the annual base flow for three subwatersheds of the Essex region in Southwestern Ontario, Canada. Significant differences in annual base flow estimated by linear and nonlinear reservoir algorithms are observed. In the nonlinear reservoir approach, the recession parameter is considered to be a seasonally variable parameter. The nonlinear reservoir approach fits streamflow recession better than the linear reservoir approach. The steeper slopes of seasonal flow duration curves in the 90% to 100% flow exceedance range show that the groundwater contribution to streamflow is relatively small in the study area. The precipitation-streamflow relationships show faster response of base flow during the period of high recharge. All of the methods show similar base flow estimation during the period of high evapotranspiration losses. The nonli...

Second-Order Autoregressive Model-Based Likelihood Function for Calibration and Uncertainty Analysis of SWAT Model

AbstractSecond order autoregressive [AR(2)] model has been adopted in the likelihood function to calibrate the soil and water assessment tool (SWAT) model for the Canard River watershed, southwestern Ontario, Canada. The Bayesian approach is used for uncertainty analysis of SWAT modeling. The performance of AR(2) model for uncertainty estimation is evaluated by the index called Percentage of observations bracketed by the unit confidence interval (PUCI) for 95% confidence limits. The results are compared with the simple least square (SLS) method of calibration. In the SLS method, the modeling errors are assumed to be uncorrelated. The study reveals that the model parameter uncertainty is high and there exists local optimum values in the parameter space. The reliability of streamflow simulation uncertainty due to parameter uncertainty is increased when AR(2) model is implemented in the calibration process. The comparison of PUCI values between AR(2) method and SLS method shows that the estimation of streamf...

On Fluid Flow and Heat Transfer in a Pipe With a U-Bend

Vertical ground source heat pumps operate by pumping a heat transfer fluid through a pipe buried in the ground. There is a U-Bend at its deepest point to return the fluid to the surface. Incidentally, the U-Bend does more than packing the extensive length of the heat transferring conduit within a single compact borehole. Large flow structures called Dean’s vortices are generated in the bend and these, along with the resulting turbulence produced, are known to significantly enhance the heat transfer processes, and hence, shorten the required length. This study examines the specific roles of Reynolds and Dean numbers on the flow structure and the resulting heat transfer in a pipe with a U-Bend. Water flowing in a pipe without and with heated wall was simulated using FLUENT. The model was verified based on available data in the literature. The efficacy of the local heat transfer rate along the pipe was cast with respect to the subtle changes in the flow characteristics under varying Reynolds number and Dean number.Copyright

Simulation of Colloidal Silica Grout Injection Using Shear Effects

The colloidal silica grout systems are being investigated for environmental containment barriers and ground improvement. Colloidal silica (CS) grout system behaves as a fluid but reacts after a predetermined time to form a solid, semi-solid or gel. These solid or semi-solid gels offer several orders of magnitude reduction in hydraulic conductivity in the porous media. A numerical model is developed to simulate chemical grouting into porous media by combining a groundwater flow simulation model (MODFLOW) and a 3D multi-species reactive transport model (RT3D). The methods to estimate the grout gel viscosity as a function of gel cure time (gel age), shear rate, and grout concentration are incorporated. The non-uniform gel viscosity is indirectly incorporated into MODFLOW by changing the effective hydraulic conductivity in each cell. The present model is used to analyse the experimental observations on colloidal silica grout injection into a sand column. The model was able to reproduce the observed injection pressures to a large extent. It has been shown that the shear effect needs to be incorporated in the grout gelation model. The model will help in better understanding the physics of grouting, the processes taking place and identifying the parameters.

Multi-objective autocalibration of SWAT model for improved low flow performance for a small snowfed catchment

ABSTRACT A reliable modelling framework needs to ensure that the model is simulating reality with limited uncertainty, thus enhancing its predictive ability. In the literature, hydrological model assessment using one or more metrics is reported to be inadequate when the river flow regime is required to be reproduced comprehensively. This research is aimed to: (a) calibrate the Soil and Water Assessment Tool (SWAT) based on the concept of multi-objective optimization by applying the Borg multi-objective evolutionary algorithm (MOEA); (b) apply hydrological signatures as objective functions; and (c) adopt a multi-metric approach for model evaluation. The SWAT model was coupled with a relatively newer and powerful Borg MOEA. The inclusion of hydrological signatures as objective functions along with the conventional statistical functions assisted in improving the performance for low flows by 135% in terms of volume efficiency and 65% for flow time series simulation.

Ground source heat pumps: should we use single U-bend or coaxial ground exchanger loops?

Ground source heat pumps are becoming more common as traditional energy costs rise. Innovative pipe loop configurations promise increased performance and efficiency. The coaxial ground loop is among these new systems. The working fluid flows through a pipe to the depth of the system and returns to the surface through a larger annulus surrounding the delivery pipe. This study compares the coaxial and the single U-bend. By use of numerical CFD modelling, it was found that the coaxial performs both better than the U-bend but also exhibits a smaller pressure loss over equal lengths. It was found that the residence time of the fluid in the loop affects the heat transfer greatly, but the U-bend was affected more than the coaxial. Thus, coaxial ground loops are essential for efficient design and performance.

Effect of heterogeneity scale on chemical grouting in porous media

Performance of chemical grouting as a containment technology is investigated through a numerical modeling study. A new grouting model that couples MODFLOW [1] and RT3D [2] combined new modules for the gelling process is presented. The present study is aimed at understanding the role of heterogeneity on grout curtain performance. The paper addresses two important issues related to heterogeneity and grid resolution: (1) relative influence of small-scale heterogeneity and large-scale heterogeneity, and (2) effect of numerical grid resolution on predicted curtain performance. Monte-Carlo simulations with statistically equivalent heterogeneous hydraulic conductivity ( K ) fields are conducted to assess the uncertainty of the grout performance. Grid resolution adequacy is determined by generation of heterogeneous K -fields at a coarse resolution and completing simulations using grid resolution equal to the K -field resolution and then refining that grid up to five times. Comparison of results at different grid resolution provides estimates of increased error associated with grid coarsening. Using the optimal grid resolution, effect of large-scale and small-scale heterogeneity is explored using simulations that incorporate primary and secondary heterogeneity each with different correlation lengths and variability and comparing to simulations having only large-scale heterogeneity. Grout curtain performance is assessed by simulation of grout injection, determinatin of post-grouted conductivity field, and assessment of overall grout curtain hydraulic conductivity using a flow model.