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Tag: hydrology
  • Post-wildfire Curve Number Estimates for the Southern Rocky Mountains in Colorado, USA

    Abstract: The curve number method first developed by the USDA Soil Conservation Service (now the Natural Resources Conservation Service) is often used for post-wildfire runoff assessments. These assessments are critical for land and emergency managers making decisions on life and property risks following a wildfire event. Three approaches (i.e., historical event observations, linear regression model, and regression tree model) were used to help estimate a post-wildfire curve number from watershed and wildfire parameters. For the first method, we used runoff events from 102 burned watersheds in Colorado, southern Wyoming, northern New Mexico, and eastern Utah to quantify changes in curve number values from pre- to post-wildfire conditions. The curve number changes from the measured runoff events vary substantially between positive and negative values. The measured curve number changes were then associated with watershed characteristics (e.g., slope, elevation, northness, and eastness) and land cover type to develop prediction models that provide estimates of post-wildfire curve number changes. Finally, we used a regression tree method to demonstrate that accurate predications can be developed using the measured curve number changes from our study domain. These models can be used for future post-wildfire assessments within the region.
  • User Guidelines on Catchment Hydrological Modeling with Soil Thermal Dynamics in Gridded Surface Subsurface Hydrologic Analysis (GSSHA)

    Abstract: Climate warming is expected to degrade permafrost in many regions of the world. Degradation of permafrost has the potential to affect soil thermal, hydrological, and vegetation regimes. Projections of long-term effects of climate warming on high latitude ecosystems require a coupled representation of soil thermal state and hydrological dynamics. Such a coupled framework was developed to explicitly simulate the soil moisture effects of soil thermal conductivity and heat capacity and its effects on hydrological response. In the coupled framework, the Geophysical Institute Permafrost Laboratory (GIPL) model is coupled with the Gridded Surface Subsurface Hydrologic Analysis (GSSHA) model. The new permafrost heat transfer in GSSHA is computed with the GIPL scheme that simulates soil temperature dynamics and the depth of seasonal freezing and thawing by numerically solving a one-dimensional quasilinear heat equation with phase change. All the GIPL input and output parameters and the state variables are set up to be consistent with the GSSHA input-output format and grid distribution data input requirements. Test-case simulated results showed that freezing temperatures reduced soil storage capacity, thereby producing higher peak and lower base flow. The report details the functions and format of required input variables and cards, as a guideline, in GSSHA hydrothermal analysis of frozen soils in permafrost active areas.
  • Assessing Differences in the Wetland Functional Capacity of Wet Pine Flatwood Compensatory Mitigation Sites Managed with Prescribed Fire and Mechanical Mowing

    Abstract: This report assesses the functional capacity of wet pine flatwood wetland habitats in the Gulf Coastal region of the United States, with a specific focus on compensatory mitigation sites maintained using mowing or prescribed fire, or both, as understory management strategies. The use of mowing in lieu of prescribed fire treatments has been proposed for a variety of reasons, including when mitigation sites are located near residential areas or where fires pose a risk to private property and public safety. This study evaluates the effects of mechanized mowing on ecosystem functions by using the hydrogeomorphic (HGM) wetland functional-assessment method to compare mitigation sites managed by mowing to sites managed by prescribed-fire regimes. Assessing mowing as a vegetation-control strategy in lieu of prescribed-fire regimes provides valuable information that can improve the design and management of wet pine flatwoods mitigation sites throughout portions of the southeastern United States, where this wetland class occurs.
  • A Regional Guidebook for Applying the Hydrogeomorphic Approach to Assessing Wetland Functions of Forested Riverine Wetlands in Alluvial Valleys of the Piedmont Region of the United States

    Abstract: The Hydrogeomorphic (HGM) approach is used for developing and applying models for the site-specific assessment of wetland functions. It was initially designed for use in the context of the Clean Water Act Section 404 Regulatory Program permit review process to analyze project alternatives, minimize impacts, assess unavoidable impacts, determine mitigation requirements, and monitor the success of compensatory mitigation. However, a variety of other potential uses have been identified, including the design of wetland restoration projects, projecting ecological outcomes, developing success criteria and performance standards, and adaptive monitoring and management of wetlands. This guidebook provides an overview of the HGM approach including classification and characterization of the principal alluvial riverine wetlands identified in the Piedmont physiography. Eight potential subclasses of Piedmont wetlands, including Headwater, Low- and Mid-gradient Riverine, Floodplain Depression, Footslope Seeps, Flats, Precipitation Depressions, and Fringe wetlands were recognized. However, the occurrence of Flats, Precipitation Depressions, and Fringe wetlands in the Piedmont, are uncommon and not generally associated with alluvial riverine systems which is the subject of this Guidebook. Detailed HGM assessment models and protocols are presented for the five most common Piedmont riverine subclasses: Headwater, Low- and Mid-gradient Riverine, Floodplain Depression, and Footslope Seep. For each wetland subclass, the guidebook presents (a) the rationale used to select the wetland functions considered in the assessment process, (b) the rationale used to select assessment models, and (c) the functional index calibration curves developed from reference wetlands used in the assessment models. The guidebook outlines an assessment protocol for using the model variables and functional indices to assess each wetland subclass. The appendices provide field data collection forms. In addition, an automated spreadsheet model is provided to make calculations.
  • Geomorphic Assessment of the St. Francis River: Between Wappapello Lake and Lake City

    Abstract: The St. Francis River is a complex system that lies in the historic floodplain of the Mississippi and Ohio Rivers. The basin has undergone extensive anthropogenic modifications, including reservoir construction, large-scale channelization, and construction of leveed floodways. Several analyses of available gage data, lidar data, and historical research have provided a picture of geomorphic trends and an overall understanding of the river’s stability. The types of analysis used to determine trends included yearly low stage plots, stage-duration curves, specific gage analysis, water surface slopes, and stream power changes. The results from these analyses were synthesized to develop an overall assessment of the reach. Channel cutoffs resulted in a significant decrease in channel length and sinuosity and triggered geomorphic change throughout the river. Immediately following channelization, dramatic decreasing trends in stage were observed for Fisk and Dekyn’s Store, while St. Francis and Holly Island began to aggrade. Slopes and stream power were significantly increased for the upper portion of the study area and showed a decreasing trend for the lower reach.
  • Mississippi River Climate Model–Based Hydrograph Projections at the Tarbert Landing Location

    Abstract: To better understand and prepare for the possible effects associated with potential climate changes on the lower Mississippi River, the State of Louisiana Coastal Protection and Restoration Authority sought information on the historical, current, and projected future hydrodynamics of the Mississippi River. To this end, flow duration curves (FDC) for the Tarbert Landing location were generated, based on climate models derived from two of the four scenarios of the Coupled Model Intercomparison Project, Phase 5 (CMIP5), multimodel ensemble representative concentration pathways (RCPs). The global CMIP5 datasets were used by the variable infiltration capacity land surface model to produce a runoff dataset, using a bias-correction spatial disaggregation approach. The runoff datasets were then applied to simulate streamflow using the Routing Application for Parallel computatIon of Discharge (RAPID) river routing model. Based on the streamflow, FDCs were calculated for 16 CMIP5 as well as observed historical data at the Tarbert Landing location. Key observations from the results are that the 90th percentile exceedance of the simulated versus the observed flows is more frequent for the RCP 8.5 scenario than for the RCP 4.5 scenario and that the maximum annual flows for the RCP 8.5 scenario are generally smaller than for the RCP 4.5 scenario.
  • Stormwater Management Practices, Monitoring, and Maintenance Plan for US Army Garrison at West Point, NY

    Abstract: Structural stormwater management practices (SMPs) are designed and installed with the goal of reducing runoff and improving water quality through a variety of built (e.g., underground chamber and filter systems), nature-based and natural features (e.g., rain gardens, swales). In compliance with Section 402 of the US Clean Water Act (CWA), US Army Garrisons at West Point MS4 operators are required to obtain a National Pollutant Discharge Elimination System permit or a New York State Pollutant Discharge Elimination System (SPDES). These permits require development of stormwater management plans to reduce pollutants to meet the appropriate water quality standards. Over 62 structural SMPs have been installed at the US Army Garrison (USAG) to meet permit requirements. Monitoring and maintenance are essential to maintain and understand the effectiveness of these structures, track their maintenance needs, and improve their function. This document provides guidance for conducting stormwater management practice, inspection, and maintenance at the United States Army Garrison at West Point. The objectives are to inform installation managers on general SMP functions and designs, highlight key maintenance triggers affecting SMP functionality, and provide guidance on when and how to conduct inspections and maintenance actions specific to USAG SMPs and in accordance to NYS DEC.
  • Numerical Modeling of Supercritical Flow in the Los Angeles River: Part I: Adaptive Hydraulics Numerical Modeling of the 1943 Physical Model

    Abstract: The Los Angeles District of the US Army Corps of Engineers is assisting the City of Los Angeles with restoration efforts on the Los Angeles River. The city wishes to restore portions of the channelized river to a more natural state with riparian/vegetative green spaces for both wildlife and public recreation usage. The Los Angeles River provides an important role for the City of Los Angeles from a flood-control perspective, and functionality needs to be preserved when contemplating system modifications. This report details the development of an Adaptive Hydraulics (AdH) numerical model capable of representing this complex system consisting of both subcritical and supercritical flow regimes. Due to limited hydraulic data in the study area, an extensive model validation to observed data was not possible. To bridge the data gap, a numerical model was developed from a previously completed physical model study with extensive quantitative measurements and qualitative reports of hydraulic conditions. This approach allowed engineers to evaluate the effectiveness of the AdH model in representing this complex hydraulic system along with determining the best methodology to accurately represent the existing conditions. This study determined appropriate model parameters that will be utilized in further numerical modeling efforts to evaluate system modifications associated with restoration efforts.
  • Remote Sensing Tools to Support Ordinary High Water Mark Delineation

    Abstract: This document is a technical note (TN) that describes existing and recently developed tools to support ordinary high water mark (OHWM) identification and delineation. It also presents a case study to demonstrate how utilizing the tools provide supporting lines of evidence in OHWM delineations.
  • National Ordinary High Water Mark Field Delineation Manual for Rivers and Streams : Interim Version

    Abstract: The ordinary high water mark (OHWM) defines the lateral extent of nontidal aquatic features in the absence of adjacent wetlands in the United States. The federal regulatory definition of the OHWM, 33 CFR 328.3(c)(7), states the OHWM is “that line on the shore established by the fluctuations of water and indicated by physical characteristics such as [a] clear, natural line impressed on the bank, shelving, changes in the character of soil, destruction of terrestrial vegetation, the presence of litter and debris, or other appropriate means that consider the characteristics of the surrounding areas.” This is the first manual to present a methodology for nationwide identification and delineation of the OHWM. A two-page data sheet and field procedure outline a weight-of-evidence (WoE) methodology to organize and evaluate observations at stream sites. This manual presents a consistent, science-based method for delineating the OHWM in streams. It also describes regional differences and challenges in identifying the OHWM at sites disturbed by human-induced or natural changes and illustrates how to use remote data to structure field inquiries and interpret field evidence using the principles of fluvial science. The manual demonstrates that, in many landscape settings, the OHWM may be located near the bankfull elevation.