In SGronsdahl/Geomorphic-Approach:

Introduction

This document provides an overview of the Geomorphic Instream Flow Tool. This tool is comprised of three components: (1) a reach averaged hydraulic simulator, (2) statistical distributions of depths and velocity, and (3) a regime model that can be used to predict how environmental change could affect model boundaries. This model is designed to be a simple and cost effective approach for conducting instream flow assessments that requires less data inputs and specialized knowledge compared to more conventional approaches.

This document is primarily focused on the implementation of the the geomorphic tool. Readers who are interested in the theoretical underpinnings of the this approach are referred to McParland et al. (2016) for information on the hydraulic simulator, Saraeva and Hardy (2009) and Schweizer et al. (2007) for information on the statistical distributions, and Eaton et al. (2004) for information on the regime model. Additionally, Gronsdahl et al. (XXXX) have conducted an evaluation of the Geomorphic Approach.

This document includes infomration relevant to data collection, data processing, and model implementation.

Model Overview

The ASHGS is a new method for evaluating the hydraulic component of instream flow assessments that is designed to be implemented using minimal data inputs, reduce fieldwork, and provide considerable cost-savings to implement when compared to conventional approaches. The data inputs that are required to execute ASHGS are relatively minimal and can be collected during one field visit that does not need to coincide with specific flow conditions. The ASHGS method is based around the prediction of reach-averaged channel hydraulics paired with statistical frequency distributions to represent the range of expected hydraulic conditions. A feature of this approach that differentiates it from conventional approaches is that it can be implemented in tandem with the University of British Columbia Regime Model (UBCRM), which is a geomorphic tool that can predict how changes in streamflow regime, land cover, or other environmental variables would impact stream morphology (Eaton et al., 2004). Pairing ASHGS and UBCRIM provides a means to assess ‘what-if’ scenarios regarding how flow diversions, land-use or climate change could affect stream morphology and fish habitat.

The hydraulic geometry input parameters are used to estimate an index of channel shape (b) that ranges from 0 (rectangular channel) to 1 (highly skewed channel) following the approach of Ferguson (2003). Then, ASHGS predicts a cumulative depth distribution, which represents an idealized reach cross-section at bankfull conditions. To simulate below bankfull conditions, the model iteratively drops the water level to evaluate how the depths change. For each water level, mean velocity is estimated using the variable power-law flow resistance equation presented by Ferguson (2007), which has been shown to more accurately represent the hydraulics of small-medium sized gravel rivers than other common flow resistance equations, including Manning’s equation. For each modelled water level, statistical frequency distributions are paired with the reach-averaged outputs to generate an estimate of the reach-averaged depth and velocity distributions. These hydraulic outputs are then coupled with a statistical frequency distribution to estimate an expected range of depths and velocities at each simulated water level. These outputs can then be paired with habitat suitability curves to generate a habitat-streamflow relationship.

Data Requirements

The input parameters for the Geomorphic Approach are as follows:

• Channel gradient, in m/m (S). This field is mandatory.
• Bankfull width, in m (Wb). This field is mandatory.
• mean bankfull depth (db). This field is mandatory.
• the maximum bankfull depth (dbmax). This field is optional. If included, it will be factored into the calculations of the b-value.
• 84th percentile of bed grain size in mm (i.e. the grain size of which 84% of the bed is finer, D84).

In addition, the R-function has also provided an ability to specify a b-value for

Install Package

The 'devtools' package is needed to install the AASHGS from Github, where it is hosted.

# install and load devtools
#install.packages(devtools)
#library(devtools)

# install and load AASHGS
#install_github("SGronsdahl/AASHGS")
#library(AASHGS)

References

This function executes a model designed and presented in the following reference:

McParland D, Eaton B, Rosenfeld J. 2016. At-a-station hydraulic geometry simulator. River Research and Applications 32 (3): 399-410

Aknowledgements

Help developing this script was provided by Jordyn Carss, Dan Moore, Brett Eaton, and Jordan Rosenfeld. Habitat suitability were developed by Ron Ptolemy.

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SGronsdahl/Geomorphic-Approach documentation built on Oct. 10, 2020, 12:41 a.m.