Monte-Carlo Simulation and Analysis (mcsa) For 1d Hecras Sediment Transport Modeling: A Case Study In The Navajo and Blanco Rivers of The San Juan Mountains, Co

The goal of the Monte-Carlo Simulation and Analysis (MCSA) is to help users quickly set up and implement Monte-Carlo simulations for Unsteady Flow and Sediment Transport modeling using HEC-RAS. The MCSA produces probabilistic results for various simulation outputs, so that sensitivities of model results to various parameters, boundary conditions and models can be systematically explored. Perturbations can be correlated with distinct reach characteristics. MCSA consists of 16 modules, eight modules from the Python standard library and three 3rd-party. Some of the 16 developed modules contain customized quality/validity checks to guarantee robustness of the software. The checks are constructed to print out both error and warning messages when anomalies are detected to provide users with the information for correction. The perturbations to HEC-RAS parameters and boundary conditions are classified based their unique variation characteristics for random sample generation in MCSA. At a specific location, Manning’s roughness coefficient and cross-sectional profile have a single value perturbation. Flow and sediment time series contain a series of values. Bed gradation distribution is also a series of sample grain fractions with the constraint that the sum of the fractions equals to one. Simulations begin with a well conceived, constructed, and calibrated model of the desired simulation. Perturbations of the user best estimates are defined by various distributions. Care must be demonstrated by the user to ensure statistical robustness. The Bureau of Reclamation designed, constructed, maintains, and operates the San Juan-Chama Project. The inter-basin transfer project consists of three diversion dams in the headwaters of the San Juan Mountains, a 27-mile long tunnel through the mountains, and Heron Reservoir. Sediment management at Blanco and Navajo River diversions is costly and difficult. Wildfires pose a serious risk to continued project operation. Changes to the downstream hydrologic and sediment regime have dramatic impacts to morphology and ecosystems. The absence of gravel in the stream bed reduces habitat quality for desired fish species. The desire for gravel augmentation downstream, without the fine material that will clog up habitats with mud, represents a challenge and opportunity for sediment management at the diversion dams. Sediment transport modeling is used to characterize the downstream systems and the required hydraulic conditions to transport the desired size classes. The MCSA is used to show 1) the sensitivity of model results to parameters of interest, 2) the distribution of likely outcomes at locations of interest, and 3) a representation of the uncertainty associated with various input boundary conditions and parameter sets.