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The agriculturally productive San Joaquin Valley faces two severe hydrologic issues: persistent groundwater overdraft and flooding risks. Capturing flood flows for groundwater recharge could help address both of these issues, yet flood flow frequency, duration, and magnitude vary greatly as upstream reservoir releases are affected by snowpack, precipitation type, reservoir volume, and flood risks. This variability makes dedicated, engineered recharge approaches expensive. Our work evaluates leveraging private farmlands in the Kings River Basin to capture flood flows for direct and in lieu recharge, calculates on-farm infiltration rates, assesses logistics, and considers potential water quality issues. The Natural Resources Conservation Service (NRCS) soil series suggested that a cementing layer would hinder recharge. The standard practice of deep ripping fractured the layer, resulting in infiltration rates averaging 2.5 in d(-1) (6 cm d(-1)) throughout the farm. Based on these rates 10 acres are needed to infiltrate 1 cfs (100 m(3) h(-1)) of flood flows. Our conceptual model predicts that salinity and nitrate pulses flush initially to the groundwater but that groundwater quality improves in the long term due to pristine flood flows low in salts or nitrate. Flood flow capture, when integrated with irrigation, is more cost-effective than groundwater pumping.

This work surveys the performance of several empirical models, all recalibrated to a common data set, that were developed over the past 25 years to relate freshwater flow and salinity in the San Francisco Estuary (estuary). The estuary's salinity regime--broadly regulated to meet urban, agricultural, and ecosystem beneficial uses--is managed in spring and certain fall months to meet ecosystem objectives by controlling the 2 parts per thousand bottom salinity isohaline position (referred to as X2). We tested five empirical models for accuracy, mean, and transient behavior. We included a sixth model, employing a machine learning framework and variables other than outflow, in this survey to compare fitting skill, but did not subject it to the full suite of tests applied to the other five empirical models. Model performance was observed to vary with hydrology, year, and season, and in some cases exhibited unique limitations as a result of mathematical formulation. However, no single model formulation was found to be consistently superior across a wide range of tests and applications. One test revealed that the models performed equally well when recalibrated to a uniformly perturbed input time-series. Thus, while the models may be used to identify anomalies or seasonal biases (the latter being the subject of a companion paper), their use as inverse models to infer freshwater outflow to the estuary from salinity observations is not expected to improve upon the absolute accuracy of existing outflow estimates. This survey suggests that, for analyses that span a long hydrologic record, an ensemble approach--rather than the use of any individual model on its own--may be preferable to exploit the strengths of individual models. [ABSTRACT FROM AUTHOR]

The hydrology of the San Francisco Bay‐Delta estuary (the Delta) has been significantly modified over the past 150 years to serve a variety of human needs for water supply and food production, albeit with adverse ecological impacts. These adverse impacts, in concert with evolving societal values, have motivated change in the estuary's water management to promote ecosystem restoration goals while continuing to support human uses. Understanding historical flow patterns, as well as the environmental functions provided by these flow patterns, is critical to restoration planning. Building upon previous work on outflow trends from the Delta to San Francisco Bay, this paper evaluates historical trends in key interior Delta flows spanning nine decades (1922–2016) and presents an attribution of these trends to various anthropogenic drivers. We reconstructed historical time series records at four key locations in the interior of the Delta; these time series represent tidally‐averaged flows that are intensively managed and are of great importance to the beneficial uses of water in the region. We derived several scenario‐based flow time series at these same four locations to assist in attributing change to a variety of drivers, including reservoir and export pumping operations, in‐Delta barrier and gate operations, and upstream water diversions. Flow changes were measured relative to 1920‐level land use and water management conditions. We find the four interior Delta locations to have distinct seasonal flow trends and, in general, unique responses to various drivers of change. Our work highlights the complex nature of historical flow changes in a highly‐managed estuarine ecosystem, and the types of modifications that would be necessary to reverse these changes. [ABSTRACT FROM AUTHOR]

Abstract: Two demonstration treatment wetland systems were studied for over four years. Both consisted of sedimentation basins, followed by wetland cells. The Imperial, CA system had four wetland cells totaling 4.7ha, 25% vegetated with bulrushes (Schoenoplectus californicus), and the Brawley, CA system had two wetland cells totaling 1.8ha, also 25% vegetated with bulrushes. Imperial received irrigation runoff water at 30cm/day, and Brawley received New River water at 11cm/day, both with moderately high levels of nutrients, sediments and pathogens. The systems seeped 40–60% of the incoming water. The hydraulic efficiencies of the systems were high because of compartmentalization and high aspect ratios. Concentration reductions of TN, TP and TSS were 50%, 39%, and 97% at Imperial, and 73%, 50% and 96% at Brawley. Imperial achieved about 1.5log10 reductions in total coliforms, fecal coliforms and Escherichia coli, while Brawley achieved about 2.7log10 reductions. The sedimentation basins settled most of the incoming TSS, as well as the algal solids that were generated in the basins. Algal uptake removed nutrients in the basins, which were supersaturated with oxygen. The wetlands were effective in denitrification, and trapped the remaining and generated TSS. Removal rate constants, corrected for infiltration, were at the high end of those reported for other wetlands. [Copyright &y& Elsevier]

The Everglades Phosphorus and Hydrology (EPH) model was developed to simulate water movement and phosphorus transport in the Everglades Protection Area which is comprised of the Everglades National Park (ENP) and surrounding wetlands known as the Water Conservation Areas (WCAs). Water flows from the Everglades Agricultural Area (EAA) through the WCAs into Everglades National Park (ENP). The model is designed to represent the system as a series of cells in which water flows from one cell to the next. The code allows for pumped inputs and pumped outputs of water as well as sorption and removal of phosphorus through peat accretion. Model application involved dividing the system into twenty cells representing different segments of the WCAs. Inputs to each cell consisted of water pumped from the EAA (where appropriate), flow from upgradient cells, and precipitation. Outputs included pumped outputs and flow out of each cell. Using data collected by the South Florida Water Management District, the model was calibrated by matching simulated and observed flows, water elevations, and phosphorus (P) concentrations for the period 1980–1988. The model was then validated for the 1988–1992 period using the same model parameters derived from the calibration process and comparing simulated and observed values. Reasonable agreement between simulated and observed values was attained for both the calibration and validation periods. The calibrated and validated model was used to simulate the impacts on annual average total P concentrations in each cell resulting from the implementation of the management plan mandated by the Everglades Forever Act. This plan calls for the construction of six Stormwater Treatment Areas (STAs) to treat discharges from the EAA, hydrologic modifications of the system to promote sheet flow, and the implementation of Best Management Practices to reduce P runoff from individual farms. In addition, the model was used to evaluate the impact of not building one of the STAs (STA 3/4), and sensitivity analyses were conducted to determine the effects of changing STA outlet P concentrations throughout the system. Model results indicate that phosphorus concentration reductions will occur in areas near EAA discharges in response to reductions in input P concentrations. However these measures will have little impact on phosphorus concentrations for 85% of the area of the WCAs and on the water entering Everglades National Park. The scenario analyses also indicate that phosphorus concentrations throughout most of the WCAs are similar with or without the construction of STA-3/4. [ABSTRACT FROM AUTHOR]