Hydrology

Coastal development shifts natural hydrology through water redirection, increased impervious surfaces, and increased connectivity to the coastal ocean through inlets. In Southeast Florida, watershed alterations can cause flash-freshening in nearshore coastal habitats, threatening coral reef ecosystems. This study assessed the hyposalinity tolerance threshold of two prominent scleractinian corals in Southeast Florida. In a series of experiments, we determined that Montastraea cavernosa corals have an LC50 of 19 PSU but can survive for at least 21 days at an intermediately stressful salinity of 25 PSU. Porites astreoides corals demonstrated an LC50 of 19 PSU, but experienced mortality when exposed to 25 PSU for 17–18 days. Prior to mortality, corals displayed decreased polyp activity, altered coloration, and decreased tissue integrity. These data suggest that lower-volume, longer-duration releases of freshwater from reservoirs may preserve coral health in Southeast Florida.

Trends in streamflow extremes at a regional scale linked to the possible influences of four major oceanic-atmospheric oscillations are analyzed in this study. Oscillations considered include: El Niño Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), Atlantic Multidecadal Oscillation (AMO), and North Atlantic Oscillation (NAO). The main emphasis is low flows in the South-Atlantic Gulf region of the United States. Several standard drought indices of low flow extremes during two different phases (warm/positive and cool/negative) of these oscillations are evaluated. Long-term streamflow data at 43 USGS sites in the region from the Hydro-Climatic Data Network that are least affected by anthropogenic influences are used for analysis. Results show that for ENSO, low flow indices were more likely to occur during La Niña phase; however, longer deficits were more likely during El Niño phase. Results also show that for PDO (AMO), all (most) low flow indices occur during the cool (warm) phase.

Water gain/loss through seepage in the Everglades Nutrient Removal (ENR) project is a major component of the water budget. Seepage is the most difficult component to evaluate because most of its constituents cannot be directly measured. For this reason simulations from models or equations are the common procedure to estimate seepage. These procedures involve a series of assumptions and simplifications (i.e., geometry, soil parameters), which can be validated with a calibration-verification process. The accuracy of the water budget for this wetland treatment is very important because it will help to clarify and quantify, together with the nutrient mass budgets, the system efficiency in removing nutrients. Two seepage components into the project site from WCA1 are pertinent to this study: levee seepage, and subsurface seepage. This thesis addresses the quantification of the subsurface seepage by finding a set of parameters (hydraulic conductivities), which minimizes the deviations between observed and calculated values of levee seepage. Thus, the subsurface seepage is estimated with the use of a finite element, steady state seepage model. Levee and subsurface seepage account for 16 percent of the inflow pump for the two year period from August 19, 1994 through August 19, 1996.

Methodologies in GIS are used to compute stream flows for a watershed in Northern California by implementing the Clark Hydrograph Method. GIS algorithms are used to produce time area diagrams with time of concentration formula. These methods are compared to a simulation in HEC-HMS with the dimensionless TAD equation and the ModClark Method. Each GIS method is used to estimate the hydrograph for a measured rainfall event. The accuracy of each of the methods is explored using the HEC objective function, mean squared error, and other statistical measures of correlation. Advantages and limitations of the GIS methodologies are examined and topics of further study are suggested.

Significant changes in climate and their impacts are now visible in various places around the globe and are expected to become more evident in the coming decades. For each increase in temperature, there are environmental and societal consequences. It has important implications for existing water resources systems as well as for future water resources planning and management. Water accounting (identifying, quantifying and reporting information of water flow in a system) is the first step towards formulating productive and sustainable water management strategies in a region. Thus, water balance models could be an empowering tool for water resource managers to prepare for and mitigate the effects of climate change on their local hydrologic resources. This thesis offers an insight into how such a tool can be used to assess and predict future stream flow trends in an effort to mitigate or manage any potential effects.