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Graduate Research

Hydraulic assessment of notched river training structures on a portion of the Lower Mississippi River using the Adaptive Hydraulics model.
Edmund Howe. MS Thesis Spring 2017
Advisor: Dr. John J. Ramirez-Avila

River training structures are widely used to create and maintain navigable waterways, to restore rivers and channels in a more stable condition, to promote environmental benefits, and to protect people and infrastructure from damages or floods. Few historical datasets on the changes and impacts in secondary waterbodies resulting from notched river training structures are available for the Lower Mississippi River. Access to the notched training structures on the Lower Mississippi River remains difficult and inhibits data collection for monitoring efforts. This increases the need for alternative methods such as numerical models for assessing the performance of the notched training structures. A quasi-three-dimensional Adaptive Hydraulics model was assembled and used to provide a hydraulic assessment of seven notched river training structures in the Lower Mississippi River. The hydraulic assessment of the notches included assessing the impacts to navigation, the long-term trends, and the potential for aquatic wildlife habitat diversity.

Sensitivity analysis using the Latin Hypercube-OAT Method for the Conservational Channel Evaluation and Pollutant Transport System (CONCEPTS) Model.
Kubra Celik. MS Thesis Fall 2016.
Advisor: Dr. John J. Ramirez-Avila

Streambank erosion is a major problem and a major known source of sediment in impaired streams. Stream deterioration is mainly due to the excess sediment in the United States. Many models have been developed to predict streambank erosion and sediment transport in the streams. Determining the most sensitive soil-specific parameters of the CONCEPTS Model for Goodwin Creek, MS was the focus of the study. The Latin Hypercube One-factor-At-a-Time (LH-OAT) method was used to complete the sensitivity analysis on soil-specific parameters in CONCEPTS. Overall results demonstrate that erodibility and critical shear stress parameters should be determined very carefully and realistic to determine streambank erosion and sediment transport rate more accurately. This sensitivity analysis also shows the minimum effects of suction angle and cohesion on results. In this case, making an assumption in a literal range, or safely ignoring them should not cause a big variation on CONCEPTS results.

Sensitivity analysis and parameter estimation for the APEX model on runoff, sediments and phosphorus.
Yi Jiang. PhD Dissertation Fall 2016.
Advisor: Dr. Dennis D. Truax
Co-Advisor: Dr. John J. Ramirez-Avila

Sensitivity analysis is essential for the hydrologic models to help gain insight into model’s behavior, and assess the model structure and conceptualization. Parameter estimation in the distributed hydrologic models is difficult due to the high-dimensional parameter spaces. Sensitivity analysis identified the influential and non-influential parameters in the modeling process, thus it will benefit the calibration process.

This study identified, applied and evaluated two sensitivity analysis methods for the APEX model. The screening methods, the Morris method, and LH-OAT method, were implemented in the experimental site in North Carolina for modeling runoff, sediment loss, TP and DP losses. At the beginning of the application, the run number evaluation was conducted for the Morris method. The result suggested that 2760 runs were sufficient for 45 input parameters to get reliable sensitivity result.

Sensitivity result for the five management scenarios in the study site indicated that the Morris method and LH-OAT method provided similar results on the sensitivity of the input parameters, except the difference on the importance of PARM2, PARM8, PARM12, PARM15, PARM20, PARM49, PARM76, PARM81, PARM84, and PARM85. The results for the five management scenarios indicated the very influential parameters were consistent in most cases, such as PARM23, PARM34, and PARM84. The “sensitive” parameters had good overlaps between different scenarios. In addition, little variation was observed in the importance of the sensitive parameters in the different scenarios, such as PARM26.

The optimization process with the most influential parameters from sensitivity analysis showed great improvement on the APEX modeling performance in all scenarios by the objective functions, PI1, NSE, and GLUE.

Methodology development for the measurement and analysis of sediment oxygen demands and nutrient releases.
Luis A. Laurens Vallejo. Fall 2016.
Advisor: Dr. James L. Martin

Sediment oxygen demand (SOD) and nutrients releases from the bottom sediments of a water body are important parameters to be included in studies of water quality processes. Two methods to measure SOD, in situ and at laboratory, were applied at Eckie’s Pond on late spring of 2015. Based upon preliminary results, which showed greater values for the in situ method, some modifications of procedures and equipment were made to improve the measurements. Another set of measurements were made on June of 2016, however their results were not conclusive to establish a correlation between these methodologies. As a result of this research, three standard operating procedures (SOP) have been established to measure SOD at shallow waters, first in situ, second at laboratory, and a third SOP to analyze nutrients and metals by using a spectrophotometer.