Effects of reducing river flow on pulse residence time in Little Manatee River, USA

Abstract

Abstract：Residence time is an important indicator for river environmental management. In this paper, a 3D hydrodynamic model has been successfully applied to Little Manatee River to characterize the mixing and transport process and residence time. The model employs horizontal curvilinear orthogonal grids to represent the complex river system that consists of branches and bayous. The model has been satisfactorily calibrated and verified by using two continuous data sets. The data sets consist of hourly observations of all forcing boundaries, including freshwater inputs, tides, winds, salinity and temperatures at bay boundary, and air temperatures for model simulations. The data sets also consist of hourly observations of water levels, salinity, and temperature at several river stations. The calibrated and verified hydrodynamic model was used to predict residence time in the Little Manatee River. Under the minimum flow of 0.312 m 3 /s, the pulse residence time (PRT) is 108 days. Model simulations were also conducted for 17 flow scenarios. Empirical regression equations have been satisfactorily derived to correlate PRT to freshwater inflow. Correlation coefficient R 2 is 0.982 for PRT.Keywords：hydrodynamic modeling；estuary；residence time；tidal river Little Manatee River (LMR) is a tidal estuary located in the southwest of Tampa Bay. The LMR originates in a swampy area in the east of Fort Lonesome in southeastern Hillsborough County and flows generally westward for about 40 miles toward its discharge point into Tampa Bay near Ruskin. Florida statutes require Southwest Florida Water Management District to establish and implement Minimum Flows and Levels (MFLs) for certain priority water bodies within their respective jurisdictional boundaries. The Florida statutes defines the minimum flow for a given watercourse as "the limit at which further withdrawals would be significantly harmful to the water resources or ecology of the area " . When a river or stream drops below its minimum flow, the aquatic life of that ecosystem can be harmed. The flow of rivers and streams also impacts fresh water and salt water mixing in estuaries. Many fish species in coastal Florida are estuarine dependent, meaning they spend part of their development in an estuary environment. Without enough fresh water flowing in from rivers and streams, an estuary becomes saltier, disrupting the delicate balance of life. In coastal areas, when water levels in the aquifer drop too low, salt water from the Gulf of Mexico can creep, or intrude, further into the freshwater aquifer, the source of 80% of the District′s drinking water. Once this happens, that part of the aquifer becomes mineralized and requires a special treatment process to purify it to drinking water or irrigation standards.This paper presents the application of a 3D hydrodynamic model to support the water resource management for minimum flows and levels for the tidal reach of the LMR. A key element for adopting minimum flows for the LMR is a sound understanding of salinity transport process...

Field and modelling investigations of fresh-water plume behaviour in response to infrequent high-precipitation events, Sydney Estuary, Australia

“…Additionally EFDC has been utilised for hydrodynamic and water quality studies in the Asia Pacific, including the Yellow Sea between mainland China and the Korean Penisula (Luo & Li, 2009), Kwang-Yang Bay, Korea (Park et al, 2005) and the Tasman/Golden Bay system in New Zealand (Tuckey, et, al., 2006). The modelling package is capable of simulating one or multidimensional flow, transport and bio-geochemical processes in a variety of aquatic systems and has been successfully applied to lakes, rivers, reservoirs, estuaries, coastal lagoons, bays and wetlands (Hamrick, 1992b;Zarillo and Surak, 1995;Yang, 1996;Kuo et al, 1996;Zarillo, 1998;Shen et al, 1999;Ji et al, 2000;Lin and Kuo, 2003;Shen and Haas, 2004;Park et al, 2005;Shen and Lin, 2006;Lin et al, 2007Lin et al, , 2008aXu et al, 2008;Liu et al, 2009;Huang et al, 2009). EFDC has the capacity to model eutrophication processes, sediment transport and fate of dissolved and particulate phases of contaminants.…”

Response Characteristics of the Perdido and Wolf Bay System to Inflows and Sea Level Rise

“…The age determined in this study is the time elapsed since a dissolved substance was discharged into the upstream rivers of an estuary. Several studies related to the age of water, flushing time, and residence time have been conducted to understand mixing and transport processes [9,12,13]. Flushing time, residence time, and age of water are three common transport timescales used to measure retention of water or scalar quantities.…”

Investigation of hydraulics transport time scales within the Arvand River estuary, Iran

“…The time that a mass of tracer will remain within the system is called residence time (Zimmerman, ). Residence time also has different forms of calculation, such as pulse residence time (PRT) (Miller and McPherson, ; Sheldon and Alber, ; Abdelrhman, ; Huang and Liu, ), estuarine residence time (ERT) (Miller and McPherson, ; Chen, ) and using remnant function integration (Takeoka, ; Huang and Liu, ).…”