OTTAR 0.2.0

Ode To Transient (Ancho de los) Rivers: Transient evolution of river-channel width

OTTAR

Ode To Transient (Ancho de los) Rivers

Transiently evolving river-channel width as a function of streambank properties, sediment in transport, and the hydrograph.

Purpose

This model is designed to compute the rates of river-channel widening and narrowing based on changing hydrological regimes. It is currently designed for rivers with cohesive banks, with a critical shear stress for particle detachment and an erosion-rate coefficient.

Structure

OTTAR contains:

• The RiverWidth class, which contains methods to evolve the width of an alluvial river.
• The FlowDepthDoubleManning class, which is used to estimate flow depth from discharge, even with an evolving river-channel geometry.

Model inputs and outputs

Inputs

Key input parameters (RiverWidth)

Variable	Description	Typical value(s)
h_banks	Stream-bank height. This is the thickness of material that must be removed for the river to widen by one unit lateral distance.	1-5 m
S	Channel downstream-directed slope. This is used to compute shear stresses and (if necessary) flow depth from water discharge.	10-3
tau_crit	Critical shear stress required to start eroding muddy banks. At this stress, the flow begins to be able to detach particles. When set up to perform an inversion using data on river widening and past flows, this is one of two key parameters to be estimated for rivers with detachment-limited banks.	1–10 Pa
k_d	Erosion-rate coefficient. This determines the rate of erosion as a function of shear stress above critical. When set up to perform an inversion using data on river widening and past flows, this is the other of two key parameters to be estimated.	~10-7 m / (Pa s)
k_n	Narrowing coefficient. This modulates the efficiency of channel narrowing via lateral sediment transport and deposition. It may relate to bar/bank structure and/or to vegetation growth and its ability to trap and stabilize sediment.	~10-2
b0	Initial width. Starting width of a channel	1–1000 m

Key input data sets and parameters (FlowDepthDoubleManning)

This step is used to compute flow depths from a discharge time series, and may be skipped if you already posess a time series of flow depth

• Discharge time series
• Manning's n (channel)
• Roughness / topogrpahy coefficient (floodplains)
• Depth / topography exponent (floodplains)

Outputs

This program outputs a time series of channel width, b(t). It organizes this within a Pandas DataFrame that can also be exported using the write_csv() function within the RiverWidth class.

Plots can also be made of just river width (plotb()) or of discharge and river width (plotQb).