Characterization of residence time variability in a managed monomictic reservoir

Abstract

[1] The average length of time land-borne compounds remain within an aquatic system is one of the key parameters controlling its biochemical processes. This study explores the magnitude and sources of daily, seasonal, and interannual variability of river water residence time in the Sau Reservoir, a prototypical example of a Mediterranean water supply. Daily estimates of residence time from 1998 to 2005 were obtained from a series of tracer experiments simulated with a one-dimensional physical model, based on actual observations and synthetic scenarios. Results highlight that multiple in situ factors, both natural and managed by humans, affect the residence time in reservoirs. Simulated residence times varied on average $30% on a daily basis, as a result of natural meteorological (17%) and river inflow temperature (11%) variability. The management of withdrawal depths largely controlled the seasonal variations: The practice of withdrawing water from the shallowest outlet, which was close to the intrusion level of summer inflows, promoted shorter residence times in summers than winters. Interannual variability was primarily associated with the natural variability of inflow volume (25%), and secondarily with surface meteorology (8%). Excessive withdrawals prior to and during long dry periods, however, drastically reduced the reservoir storage capacity and withdrawal options, leading to shorter residence times in dry years. The flushing time, calculated as the ratio of storage volume and flow rates, captured the trends in annual mean residence times reasonably well but not daily and seasonal residence times.

Summer circulation and exchange in the Saginaw Bay-Lake Huron system

“…First‐order transport timescales such as residence times and flushing times within the bay are useful for understanding and interpreting the fate and transport of contaminants, nutrient budgets, and the occurrence of harmful algal blooms, and for comparing processes and rates across different ecosystems [ Monsen et al ., ]. Significant progress has been made in recent years in characterizing the transport timescales for surface water bodies using hydrodynamic and transport models [ Andutta et al ., ; Camacho and Martin , ; Phelps et al ., ; Hsu et al ., ; Wan et al ., ; Liu et al ., ; Andradóttir et al ., ; Jouon et al ., ]. Although some estimates of residence times are available for the Saginaw Bay [ Dolan , ; Saylor and Danek , ], they are nearly 40 years old and much has changed in terms of our ability to observe and model natural systems since then.…”

A simple approach to the evaluation of the actual water renewal time of natural stratified lakes

“…All these time scales are important because they provide comparison terms for other time scales related either to inputs or to biogeochemical processes within a lake. It is customary to introduce this synthesis of the complexity of the original system in many fields of science in addition to limnology and oceanography of coastal environments [e.g., Dronkers and Zimmerman, 1982;Sanford et al, 1992;Hocking and Patterson, 1994;Oliveira and Baptista, 1997;Hilton et al, 1998;Hagy et al, 2000;Monsen et al, 2002;Ambrosetti et al, 2003], where a process can be conceptualized as a reservoir with transfer of matter [e.g., meteorology, Bolin and Rodhe, 1973; sanitary engineering and waste water treatment, Tzatchkov et al, 2009; the built environment, Sandberg and Sj€ oberg, 1983].…”

“…Taking advantage of the horizontal homogenization that characterizes most stratified lakes and reservoirs, a more practical approach that has been proposed is that of reverting to 1‐D hydrodynamic models [e.g., Rueda et al ., ; Andradóttir et al ., ] to quantify the lake time scales by computing the time variation of a tracer. This approach is a compromise between physics and simplicity.…”

Do human activities affect phytoplankton biomass and composition in embayments on Lake Diefenbaker?

“…Furthermore, during the high flows events, it was evident that water was moving through Lake Diefenbaker, suggestive of rapid flushing of the reservoir at full supply level as observed in other studies (Bukaveckas et al 2002;Andrad ottir et al 2012). Because cyanobacteria require calm and low flushing rates in addition to high nutrient concentrations for their growth, they are less likely to be abundant under such condition (Huszar & Reynolds 1997;Godlewska et al 2003).…”