Construction of two dams on the Nueces River reduced environmental flow to the Nueces Marsh causing ecosystem degradation. A pipeline was built to enhance flows and restore hydrological connections between the river and marsh. Sediment and water quality has been monitored in Rincon Bayou since the pipeline was operational in 2009. Hydrologically, Rincon Bayou is still a reverse estuary that occasionally exhibits hypersaline conditions. The salinity can fluctuate from fresh to hypersaline, and hypersaline to fresh in very short time periods. Pumping from the Calallen Pool into Rincon Bayou occurs only when there is also natural inflow because that is the only time when passthrough is required. Nutrients are high when salinity is low. The diversity of macroinfauna and macroepifauna is low. There are very high fluctuations of abundance and biomass related to fluctuations in inflow. The low diversity and population fluctuations indicate the ecosystem is still disturbed. To improve the marsh, salinity should be maintained between 6 and 18 psu, minimum water depth should be between 0.2 m to 0.3 m, and to improve ecological stability inflows should be a continuous trickle, not a pulsed flood. Therefore, inflows from pumping should be continuous and not haphazard, and not dependent on pass-through requirements.

To fill the observations gap on ungauged streams, crowdsourced distributed hydrologic measurements were considered as a potential supplement for observational data networks. However, citizen science data come with uncertainty as they are provided by the general public. In order to investigate this uncertainty, a decision tree methodology was applied to evaluate existing citizen science data of stream stage based on the CrowdHydrology (CH) network. Quality control (QC) flags were developed and applied to CH sites, dividing Level 1 dataset (raw dataset) into Level 2 (flagged dataset) and Level 3 (processed dataset). Error estimates were calculated to determine uncertainty in the citizen science data. The results indicate that the decision tree could provide reliable QC for citizen science data and demonstrate how uncertainty can be quantified in the QC datasets.

A pipeline to pump water from the Nueces River to the upper delta at Rincon Bayou was constructed to mitigate the reduction of inflow from impoundments. Pumping has restored ecological function to the Nueces Estuary by increasing inflow and decreasing salinity, and transitioned the marsh into a positive estuary (lower salinities upstream increasing downstream towards the bay). Pumping has decreased the occurrences of salinities greater than 35 practical salinity units during drought conditions; however the current pumping regime causes a disturbed environment by creating extreme fluctuations in salinities in a very short time period. Immediately after pumping salinity fluctuations at the pumping outfall commence from hypersaline to fresh. When pumping ceases, salinity fluctuates from fresh to hypersaline until the next pumping event. Pumping often occurs during rainfall and flooding events when reservoir levels meet certain capacities that trigger pass-through requirements. This strategy provides inflow when it is not needed, and inhibits pumping during drought conditions when inflow is needed to maintain the quality of the estuarine ecosystem. While the current pumping regime has restored estuary conditions to Rincon Bayou by increasing inflow and decreasing salinity, it also causes extreme fluctuations in salinity that act as a disturbance. A lower magnitude, longer duration pumping strategy would create a more stable environment by providing freshwater continuously and would be an improved hydrological restoration strategy. Citation: Del Rosario EA, Montagna PA. 2018. Effects of the Rincon Bayou Pipeline on salinity in the upper Nueces Delta. Texas Water Journal. 9(1):30-49. Available from: https://doi.org/10.21423/twj.v9i1.7042.

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