**Not to be merged but for sharing idea** Diffusive prototype for coastal boundary condition and streamflow DA

[kumdonoaa]

Overview

Diffusive wave routing model was tested with hypothetical coastal boundary conditions and the results are summarized here: https://docs.google.com/document/d/11si1S2MYhOq9iKrF9aTDIMOack6Lx8BlzZSE8rGA5c4/edit
Also, the diffusive model used observed stream flow data where available to see how streamflow data assimilation can be achieved in diffusive wave.
** These tests used very ad-hoc approach such as reading text input files and temporarily assigned index for stream segments for DA. Code lines below the comment of "TODO for DA" in diffusive.f90 should replace related ad-hoc code lines.

Additions

• Reading boundary data and USGS observed data was added to diffusive.f90
• Implementing given boundary data instead of normal depth assumption was added in diffusive.f90
• Replacing assumed flow value at the bottom node of each reach by USGS-observed flow was added to diffusive.f90

Removals

Changes

Testing

1. Implementing hypothetical coastal boundary condition in the Lower Colorado River, TX

The results of this test are summarized in this document: https://docs.google.com/document/d/11si1S2MYhOq9iKrF9aTDIMOack6Lx8BlzZSE8rGA5c4/edit

2. Implementing USGS observed flow data for streamflow DA for diffusive wave routing in the Lower Colorado River, TX

The head segment of the diffusive mainstem was chosen to be at the location of USGS 08159200 Colorado Rv at Bastrop, TX. And then, the observed streamflow between 6/1/2020 12:05 and 6/4/2020 12:05 replaced assumed flow values at the bottom node of the reach having the head segment. The following animation shows the propagation of the replacement along downstream. In general, river speed is 0.7 m/s in average, so the travel distance during 3 days might be about 180 km. Indeed, we can see the deviation between DA and no DA curve is beginning at around the distance in the end of the simulation.

The next graph compares the DA-modified streamflow vs. USGS-observed streamflow in the downstream of the USGS Bastrop, TX. The gaga locates at Smithville, TX. As you can see, DA curve begin to converge to observed curve toward the end of 3 days simulation time period.

Screenshots

Notes

Todos

Checklist

• PR has an informative and human-readable title
• Changes are limited to a single goal (no scope creep)
• Code can be automatically merged (no conflicts)
• Code follows project standards (link if applicable)
• Passes all existing automated tests
• Any change in functionality is tested
• New functions are documented (with a description, list of inputs, and expected output)
• Placeholder code is flagged / future todos are captured in comments
• Visually tested in supported browsers and devices (see checklist below 👇)
• Project documentation has been updated (including the "Unreleased" section of the CHANGELOG)
• Reviewers requested with the Reviewers tool ➡️

Testing checklist

Target Environment support

• Windows
• Linux
• Browser

Accessibility

• Keyboard friendly
• Screen reader friendly

Other

• Is useable without CSS
• Is useable without JS
• Flexible from small to large screens
• No linting errors or warnings
• JavaScript tests are passing