Julie Coonrod

GIS techniques for creating river terrain models for hydrodynamic modeling and flood inundation mapping

Two- and three-dimensional (2D/3D) hydrodynamic models require the geometric description of river bathymetry and its surrounding area as a continuous surface. These surface representations of river systems are also required in mapping flood inundation extents. Creating surface representations of river systems is a challenging task because of issues associated with interpolating river bathymetry, and then integrating this bathymetry with surrounding topography. The objectives of this paper are to highlight key issues associated with creating an integrated river terrain, and propose GIS techniques to overcome these issues. The following techniques are presented in this paper: mapping and analyzing river channel data in a channel fitted coordinate system; interpolation of river cross-sections to create a 3D mesh for main channel; and integration of interpolated 3D mesh with surrounding topography. These techniques are applied and cross-validated by using datasets from Brazos River in Texas, Kootenai River in Montana, and Strouds Creek in North Carolina. Creation of a 3D mesh for the main channel using a channel-fitted coordinate system and subsequent integration with surrounding topography produces a coherent river terrain model, which can be used for 2D/3D hydrodynamic modeling and flood inundation mapping. Although techniques presented in this paper produce better results compared to existing GIS methods, the linear approach has some limitations which can be overcome by accounting for channel meanders, sinuosity and thalweg location.

Case Study: Movable Bed Model Scaling for Bed Load Sediment Exclusion at Intake Structure on Rio Grande

Results of a laboratory modeling study are presented for excluding bed load sediment from a diversion/intake structure on the Rio Grande in Albuquerque, New Mexico. To achieve model similitude, crushed coal was used to model the prototype sediment in a 1:24 scaled model with an exaggerated slope such that shear force is adequately modeled. The Shields parameters and critical Shields parameters were matched between the prototype and the model, resulting in similar grain Reynolds numbers. Twenty-four tests, where guiding walls, submerged vanes, and/or the angle of the intake bay were altered, were conducted for a single river and diversion flow rate to develop the best performing sediment exclusion system at the intake structure. Independent vanes with 45° rotated intake bays were recommended for the most effective sediment exclusion at the intake structure.

Numerical Modeling Study for Fish Screen at River Intake Channel

A numerical modeling study of hydraulic performances of an angled vertical fish screen at a river diversion intake channel that was developed using a porous media numerical scheme. Flow patterns in the intake channel induced by the fish screen were computed with a three-dimensional fluid dynamics computation program solving the Reynolds-averaged Navier-Stokes equations. Screen flow head loss coefficient were simulated and compared with the physical model values converted from the test measurements for the porous media numerical scheme applicability test. For validation of the numerical model, fish screen velocity ratio profiles of sweeping and approach were compared with physical model measurements. Different types of screen face material and baffle installations for uniform approach flow distributions were simulated. The numerical model shows very good agreement with the velocity ratio measurements, and modeling capability for different screen material types and baffle installations by controlling of the numerical model of the porous opening directions and adjustment of baffle porosities respectively.

USGS Streamflow Data and Modeling Sand-Bed Rivers

United States Geological Survey streamflow data are commonly used for hydraulic model calibration and boundary conditions. The transitory nature of sand-bed rivers’ bathymetry is problematic for the traditional automated stream gauging methods used by the USGS. This note seeks to assess the limitations of streamflow measurements for use in hydraulic models. An overview of USGS rating-curve development and use is presented with a focus on the specific challenges of sand-bed rivers. Measurements from three consecutive USGS gauges for a storm event on the Rio Grande in Albuquerque, New Mexico, illustrate the outlined problems with rating curves. These gauges are utilized to study the impact of uncertainty in rating-curve discharges on hydraulic model results. A one dimensional hydraulic model of the study reach indicates up to 25% reduction in the calculated flow depth if questionable rating-curve discharges are used as model input. Recommendations for using USGS streamflow data in hydraulic models are outlined.

Flood debris filtering structure for urban storm water treatment

A simple and effective debris removal structure, the Drop Flow Debris Filter, is developed for urban storm water channels as a best management practice. This structure consists of two almost horizontal, slightly sloped plates, one placed above the other to form a debris basin. This system allows storm water to exit through the bottom of the debris basin, while floating and heavy debris are retained in the basin. A 1 : 12 scale physical model in a flume and a three-dimensional computational fluid dynamics model were used to investigate the debris-filtering performance of the system. To achieve enhanced debris filtering, a horizontal ramp was added to the preliminary model and both plates were curved. The curved plates model showed the most successful debris filtering performance by providing a compact short-circulation zone of water with reduced separation length and increased energy loss.

Storm Water Best Management Practice: Development of Debris Filtering Structure for Supercritical Flow

A simple, but effective, debris removal structure was developed for supercritical flow in urban storm water channels. This structure was designed as a best management practice in response to the National Pollution Discharge Elimination System. The Drop Flow Debris Filter (DFDF) structure consists of two slightly sloped plates, one placed above the other to form a debris basin. The DFDF structure translates supercritical flow of the storm water channel into subcritical flow in the debris basin. This system creates flow paths that only allow water in the bottom of the basin to pass through while debris is retained in the upper part of the basin. To investigate the hydraulic performance of the DFDF structure, a 1:3 scale undistorted physical model was constructed in a 0.91 m wide plexiglass flume. This model was also created in a three-dimensional computational fluid dynamics program. Three different density spheres were used in this model study to reproduce different buoyant storm water debris. Six different DFDF designs were developed and tested, and the modified curved plates design was recommended for the best performing DFDF structure.

Hydraulic Modeling Study for Rio Grande Diversion Structure at Albuquerque

Hydraulic model tests of flow properties of diversion structure gates are presented for the proposed diversion structure on the Rio Grande at Albuquerque, New Mexico. The Rio Grande diversion structure is composed of independently controlled adjustable height gates across the channel, a fish passage through the diversion structure, and an intake channel for 3.7 m 3 /s of maximum river diversion. A 1:24 scale distorted movable bed hydraulic physical model was constructed at the Water Resources Research Laboratory of U.S. Bureau of Reclamation in Denver, Colorado. The hydraulic performances of the diversion structure that were tested include the gates operation over various flow rates, flow transitions and sediment exclusions at the intake channel. Two-dimensional hydrodynamic numerical model was built to simulate the flow properties around the diversion structure. Velocity vector computations around the intake structure and the diversion gate openings are compared with the physical test measurements. The numerical model shows very good agreements with the physical model measurements.