ATTN OFFICIAL JUDGES FOR THE STUDENT PRESENTATION COMPETITION: If you were contacted by the Conference Planning Committee Student Activities Chair, Allison Lewis, remember to use the appropriate evaluation form when scoring student participants. The link and QR code to this form was emailed to you along with your student assignments. To make identifying student participants easier, the green graduation cap
next to a session title includes a student who is participating in the
PRESENTATION Competition.
Supply Source and Natural System Sustainability Assessment and Climate Change Adaptation for Water Supply Utilities
Moderator:
Jeffrey Geurink
Presenters:
- Jeff Geurink, Tampa Bay Water, "Examining the Impact of Land Use Change on Water Resources Using the Integrated Hydrologic Model"
Land use transitions from grass, forest, and irrigated agriculture to urban have occurred for several decades and are projected to continue in the Tampa Bay, Florida area. One study indicated impervious area within the Tampa Bay watershed increased from 9% to 27% from 1991 to 2002 and was projected to increase to 38% by 2025. Besides land use transitions, many other stresses influence streamflow, springflow, and levels in lakes, wetlands, and the aquifers. Historical variability in rainfall and potential evapotranspiration (ET) and changes in well pumping, land use, and climate contribute to total changes observed and projected for flows and levels. Over the past several decades, sustainability concerns for natural systems in the Tampa Bay area have prompted regulators to impose minimum flows and levels for water bodies. To evaluate sustainability, a major water utility in the region, Tampa Bay Water, had previously investigated the impact of rainfall variability, well pumping, and projected climate change on water resources and was motivated to also examine the impact of land use change on water resources. The Integrated Hydrologic Model (IHM) is a fully-integrated hydrologic model that simulates all surface-water and groundwater processes and their dynamic interactions. It has been demonstrated that a calibrated IHM application for the Tampa Bay region can quantitively partition total change in flows and levels into separate climatic and anthropogenic stresses in a region covered by 25% water and wetlands with more than 50% of the area having near-surface water table. For two river watersheds within the Tampa Bay watershed (study region), landuse change from 1995 to 2010 was dominated by transitions from grass and forested land to the urban sector, which includes transitions to pervious and impervious surface and to water bodies for stormwater management. With respect to the two watershed areas of the study region, grass and forested lands decreased by 25% and 10%, having transitioned to the urban sector with about half of the transitioned area being impervious. Simulated long-term average responses include increased streamflow (12% and 3%) and decreased total ET, groundwater ET, recharge (20% and 8%), and groundwater level.
- Chin Man Mok, GSI Environmental Inc., "Improving Simulated Hydrologic Responses by Bayesian Integration of Radar and Gauged Rainfall Datal"
To support water management decision making, a calibrated application of the Integrated Hydrologic Model (IHM) was developed to simulate the hydrologic responses to rainfall and water supply operations in the Integrated Northern Tampa Bay (INTB) region. Spatial and temporal distributions of rainfall significantly impact surface water processes and the dynamic exchange between groundwater and surface water. More than 10 years ago, the model was initially calibrated using rainfall input derived from historical rain gauge data with Thiessen polygon spatial distribution method. Since rainfall is highly dynamic and spatially varied, rain gauges in some areas are spaced too far apart and do not adequately capture the spatial and temporal distribution of rainfall. They sometimes miss small-scale rainstorms entirely or over-estimate the spatial extent of the measured rainfall event, resulting in apparent “phantom storms” for some streamflow hydrographs simulated by the model. Since 1995, rainfall estimated from Next Generation Radar (NEXRAD) reflectivity data has been available in 15-minute, 2x2-kilometer resolutions. It was found that the estimation of rainfall from radar data is inherently uncertain and biased, tending to be over-estimated at lower rainfall level and under-estimated at higher rainfall level. This paper describes a Bayesian statistical approach to integrate rain gauge and NEXRAD rainfall data to produce a high-resolution representation of rainfall in the INTB region. In this Bayesian framework, the gauged data was used to develop the prior distribution and the radar rainfall uncertainty was used to derive the likelihood function. The resulting Bayesian rainfall accentuates the strengths of rain gauge and radar rainfall data while de-emphasizing their weaknesses. It agrees with the gauged data and is corrected for the radar rainfall biases. The uncertainty associated with the Bayesian rainfall is smaller than the uncertainty associated with gauged data interpolation and the inherent radar rainfall uncertainty. The Bayesian rainfall estimation has generally improved the INTB simulation accuracy. Monte Carlo realizations of future rainfall were also derived using the Bayesian rainfall. These realizations are expected to produce more reliable estimations of future surface water availability and hydrologic responses which can improve future water resources management.
- Warren Hogg, Tampa Bay Water, "Environmental Recovery in the Northern Tampa Bay Areal"
Palustrine wetlands currently make up over 25 percent of the land surface in the Northern Tampa Bay area. Ground water extraction from public supply wellfields began in this area in 1930 and increased as the local population grew. The rate of ground water extraction from 11 wellfields reached 167 million gallons per day on an annual average basis in early 2001. This high rate of sustained extraction was a contributing factor to low or absent water levels in area wetlands and the transition from wetland toward upland plant species. Elected and regulatory officials in the Tampa Bay area made historic decisions in 1998, recognizing the importance of wetlands and reducing the extraction of ground water from these 11 wellfields to no more than 90 million gallons per day. The agreements allowed us to develop alternative water supply sources, reduce ground water extraction, and meet the growing demand for water in our area. Ground water extraction from these wellfields has been reduced by half, averaging approximately 80 million gallons per day for the past 10 years. Tampa Bay Water recently completed an assessment of environmental recovery at 1,360 wetlands and lakes in this area. A comprehensive assessment of environmental recovery due to the reduced rate of ground water extraction was necessary to renew the operating permit for these wellfields. Numeric metrics of environmental health or recovery were established for wetland types covered by this study and multiple weight-of-evidence analyses were developed. A quantitative assessment of recovery was completed for all sites with long-term water level data and 85% of the lakes and wetlands fully meet their numeric metric of recovery. The remaining sites show substantial water level improvement and most of these sites missed being classified as recovered by less than one foot on a long-term basis. Full hydrologic recovery at many of these remaining wetlands is precluded by new residential development adjacent to the wellfields. Tampa Bay Water has applied to renew the operating permit for these 10 wellfields at the same extraction rate and this assessment of environmental recovery is a critical component of this permit renewal.
- Wendy Graham, Seungwoo Chang, University of Florida; Jeffrey Geurink and Nisai Wanakule, Tampa Bay Water, "Evaluation of impacts of climate change and water use scenarios on hydrology in the Tampa Bay Region"
General circulation models (GCMs) have been widely used to simulate current and future climate at the global scale. However, the development of frameworks to apply GCMs to assess potential climate change impacts on regional hydrologic systems, ability to meet future water demand, and compliance with water resource regulations is more recent. In this study eight GCMs were bias-corrected and downscaled using the bias correction and stochastic analog (BCSA) downscaling method and then used with eight water use scenarios to drive Tampa Bay Water’s Integrated Northern Tampa Bay Model (INTB). Five of eight GCMs projected a decrease in streamflow and groundwater availability in the future regardless of water use scenario. For the business as usual water use scenario all eight GCMs indicated that, even with active water conservation programs, increases in public water demand projected for 2045 could not be met from ground and surface water supplies while achieving current groundwater level and surface water flow regulations. With adoption of 40% wastewater reuse for public supply and active conservation four of the eight GCMs indicate that 2045 public water demand could be met while achieving current environmental regulations; however, drier climates would require a switch from groundwater to surface water use. These results indicate there may be a reduction in future freshwater supply in the Tampa Bay region if environmental regulations intended to protect current aquatic ecosystems do not adapt to the changing climate.