Dr. Vince Neary
Department of Civil and
Environmental Engineering
Tennessee Technological University
Prescott Hall 339
1020 Stadium Road, Box 5015
Cookeville, TN 38505-0001

Tel: (931) 372 3604
Fax: (931) 372 6239

Our Research

Urban Watersheds Research

Collaborators:
Dr. V.S. Neary (TTU, Civil Engineering), Dr. Jie Cui (TTU, Mechanical Engineering), Dr. G. Kim Stearman (TTU, Agriculture), Andrew Christensen (TTU Civil Engineering)

Urbanization significantly alters watershed hydrology and degrades water quality. The water resources group at TTU is working to develop and evaluate stormwater best management practices (BMP) to offset its impacts. Current thematic areas include: (1) Developing and improving modeling techniques to evaluate hydrologic processes and the benefits of stormwater BMP strategies in an urbanized watershed; (2) Laboratory and field evaluation of hydraulic and treatment performance of commercially available stormwater BMP technologies and extended detention basins.

Evaluating Methods and Source Data for Improved Hydrologic Prediction
The development of model parameterization methodologies using geographic information systems is becoming increasingly important in hydrologic modeling applications, especially given the continued trend of comprehensive and readily available geospatial databases. We have developed parameterization and calibration methodologies for the twelve-parameter soil moisture accounting (SMA) algorithm recently added to the Hydrologic Modeling System (HMS) program by the Hydrologic Engineering Center (HEC). Our work demonstrates that parameters for a complex soil moisture accounting model can be derived from publicly available geographic information system (GIS) databases. The accuracy of continuous hydrologic modeling can be improved using seasonal or multi-parameter sets. Parameter values after model calibration, including four parameters estimated using historic stream flow records, deviated from estimated values by an average of 37 percent. The use of radar-based precipitation was also investigated for possible improvement of spatially lumped continuous hydrologic modeling in two sub-basins of the Cumberland River basin in Middle Tennessee. Hydrologic predictions of streamflow at the outlets of the sub-basins were obtained using HEC-HMS and two precipitation inputs, Stage III radar-derived and gauge-only data. Model performance with each precipitation input was assessed by comparing predicted and measured streamflow at each sub-basin outlet and calculating streamflow volume bias, root mean square difference, mean normalized peak error, mean peak timing error. The results indicated that the Stage III precipitation suffers from systematic underestimation at both point and sub-basin scales, and cannot be completely offset by model recalibration. Simulations driven by both the Stage III and gauge-only data periodically failed to reproduce observed flood peaks in both sub-basins. But, Stage III simulations are generally less accurate in prediction of streamflow volume compared to gauge-only simulations and, although comparable to the gauge-only simulations in predicting the magnitude and time to peak, offer no apparent improvement predicting these quantities either.

Accumulation of radar images (1500 March 02 to 0800 March 03, 1997)
Note: Contours are increments of 0.10 inches of rainfall

References
Neary, V.S., E. Habib, M. Fleming (2004) "Hydrologic modeling with NEXRAD precipitation in Middle Tennessee." Journal of Hydrologic Engineering. 9(5), 339-349.

Fleming, M., and V.S. Neary (2004) "Continuous hydrologic modeling study with HEC-HMS." Journal of Hydrologic Engineering. 9(3), 175-183.

Factors Affecting Assessment of Average Watershed Slope
The sensitivity of average watershed slope, or Y-slope, in the NRCS lag time equation to digital elevation model (DEM) grid size and source were examined by using high resolution LiDAR data. The results confirm previous findings that Y-slope is inversely proportional to DEM grid size. The sensitivity of Y-slope estimates to grid resolution makes it less desirable as a slope metric compared to main channel slope, which has been shown to remain constant up to 90-m resolutions. A comparison of Y-slope estimates from LiDAR DEMs and USGS DEMs shows that those based on the USGS DEMs are systematically under biased. Differences between slope metrics and estimation methods can be significant. Y-slope estimates based on an alternative contour-based method are comparable to the DEM-based estimates. However, both estimates of Y-slope differ considerably from the main channel slope. Developers of hydrologic response time formulae should adopt standard protocols for estimating slope metrics, which consider DEM grid size and quality of source data, and dissuade users from interchanging slope metrics.

Location of USGS quadrangles used in this
study for (a) Washington and (b) Louisiana

Comparison of shaded relief maps of the Hatchersville, LA
quadrangle for 30-m LiDAR DEM (left) and 30-m USGS DEM (right).

Comparison of Y1 estimates from 30-m LiDAR DEM and 30-m USGS DEM

References
Hill, A.J. and V.S. Neary "Factors affecting assessment of average watershed slope." Journal of Hydrologic Engineering. (In Press for March 2005).

Stormwater BMP Evaluation Studies
Aqua-Swirl™ Concentrator. Swirl concentrators, or hydrocyclones, are innovative storm water best management (BMP) technologies for storm water treatment. These devices induce a vortex, which rapidly separates solids from storm water runoff. The resultant flow field is complex, highly three-dimensional and not well understood. Laboratory experiments and computational fluid dynamics (CFD) modeling were employed to resolve the 3D flow field and to evaluate the hydraulic losses and removal efficiency of one such device, the Removal efficiencies were determined for the full range of operating conditions, directly by mass balance, and indirectly by sampling influent and effluent concentrations. These studies provide information that will improve design methodologies and optimize performance through design modifications.

Schematic of Aqua-Swirl™ Concentrator

Experimental Setup, Hydraulics Lab.

3D flow simulations of swirl concentrator.

References
Neary, V.S. (2003)"Hydraulic Performance and Trap Efficiency for the Aqualswirl™ Concentrator." Final Report.

Neary, V.S., Cui, J. and P.N.V.D. Alapati (2005). "CFD Modeling Study of Hydrocyclone Separator," (In Preparation)

Stormtech® Isolator™ Row. StormTech® subsurface chambers are designed to provide underground stormwater detention storage, eliminating the need for surface detention ponds and thereby saving space. The "Isolator™" Row, a series of chambers encased in geotextile fabric, traps sediment and prevents it from moving downstream into the subsurface chambers. Laboratory experiments and testing protocols were designed to determine: (1) The hydraulic performance, i.e., the relationship between stage, storage, discharge, and detention time; (2) The percentage of injected sediment that is trapped within the system (i.e., trap efficiency) as a function of the hydraulic loading rate in gpm/ft2. This curve can be used, given a site's estimated annual sediment load, to determine the sedimentation rate in the Isolator Row, and the schedule for sediment removal; and (3) The percentage of retrievable sediment in the Isolator Row (i.e., the sediment that is not occluded in the filter fabric or washed into the gravel substrate foundation). The calculated trap efficiencies for the Isolator™ Row were found to be greater than 94% at all hydraulic loading rates. At the manufacturer's suggested nominal maximum design hydraulic loading rate (0.5 cfs per chamber), the trap efficiency remained greater than 95%. Approximately 20% of the sediment was irretrievable.

StormTech® Isolator™ Row Laboratory Experiment.

References
Christensen, A.C. and Neary, V.S. (2005)"Hydraulic Performance and Trap Efficiency for the Stormtech SC-740 Isolator Row." Final Report.

Neary, V.S., Neel, T.C., G.K. Stearman, and D.B. George (2004) "Detention basin retrofit for stormwater treatment." Novatech' 2004, 5th Intnl. Conf. on Sustainable Techniques and Strategies in Urban Water Management. Lyon, France, June 6-10, 2004.

Neary, V.S., Neel, T.C., J.B. Dewey, G.K. Stearman, and D.B. George (2002) "Pollutant Washoff and Loading from Parking Lots in Cookeville, Tennessee." 9th Intnl. Conf. on Urban Drainage. Portland, Oregon, September 8-13, 2002.

Extended Detention Basins. How can existing detention basins, which were originally designed for flood peak reduction, be retrofitted to provide some water quality benefits? This question was investigated for an actual detention basin in Cookeville, Tennessee. The performance of a detention basin was determined after redesigning the outlet structure to increase detention time and provide preferential withdrawal (skimming) near the free water surface. Specific modifications included: (1) The replacement of the low-stage orifice with a floating riser for skimming relatively clean water near the free surface; (2) The addition of a mid-stage rectangular orifice 1.1 m above the pond bottom; (3) A drop inlet raised to a height 2.6 m above the pond bottom to maintain the flood storage volume. Constraints did not allow an increase in the maximum storage volume of the detention basin. The TSS removal efficiencies for both pre- and post-retrofit basins exhibit great variability due to the wide range of hydrologic conditions observed. The average TSS removal efficiencies (38 51 % for the post-retrofit basin compared to -14 45 % for the pre-retrofit condition), while not reflecting average annual conditions due to the limited number of storms monitored, indicated improvement; as does comparison of similar events.

References
Neary, V.S., Neel, T.C., G.K. Stearman, and D.B. George (2004) "Detention basin retrofit for stormwater treatment." Novatech' 2004, 5th Intnl. Conf. on Sustainable Techniques and Strategies in Urban Water Management. Lyon, France, June 6-10, 2004.

Neary, V.S., Neel, T.C., J.B. Dewey, G.K. Stearman, and D.B. George (2002) "Pollutant Washoff and Loading from Parking Lots in Cookeville, Tennessee." 9th Intnl. Conf. on Urban Drainage. Portland, Oregon, September 8-13, 2002.