Presentation from 2018. Old logo. Same concept
1D HEC-RAS compared with 2D HEC-RAS
1 dimensional modeling for FEMA floodplains vs 2 dimensional modeling for FEMA floodplains.
My stance is until the floodplain administrators have the technical knowledge and or resources to review 2D models its not doing anyone any favors. Some agree and some do not. I have seen more and more 2D models using quais steady state modeling over large areas and in places where the model domain covers a lot of insurable structures and includes floodways. I have even seen large wood represented in RAS mapper which is interesting since wood floats and rots and moves. Are they going to tell the wood to stay put to match the model?
When I was at CDOT, we advocated for maintaining effective models in 1D and using 2D to inform the 1D models You adjust the 1D modeling based on your 2D but still have the simplicity of regulating to a 1D standard. This simplifies the job for the administrator and helps developers understand the cost and time to meet the floodplain development permit requirements.
My example work from Trinidad Colorado is here. I am not looking for technical comments on my work. This was completed a while ago and the work was done with public funds and has been shared through the local nonprofits. I am providing it as an example for comparing 1D HEC-RAS with 2D HEC-RAS. It is in an older version so the tools and components within HEC-RAS have changed a lot over the last 5 years or so.
If you have questions or want a presentation on 1D and or 2d modeling please reach out. It may help with those who are trying to learn modeling with a short course (which makes me a little nervous). There are additional results/maps in appendices comparing different flows but the file is large. I can share that as well if you are interested please email me.
Resilience planning starts before the next fire or flood
There is no such thing as channel stability except on a temporary basis.
This is Left Hand Creek diversion structure after the 2013 flood on the Colorado Front Range north of Boulder, Colorado. What we learned, and seem to have forgotten or blocked from memory, is the river finds a way. Rivers move. Mountain rivers move quickly because of high energy flow and sediment being transported. This is upstream from the mouth of the canyon where the river avulsed (escaped the banks of the normal river) on the alluvial fan.
Alluvial Fan https://en.wikipedia.org/wiki/Alluvial_fan
The solution is move the point of the diversion upstream to reduce the amount of energy, head, stored in one location. Ditches need head to keep water flowing to the reservoir. In channel concrete structures like this always fail. This structure was still in place after the project was completed. The low flow channel in the photo was replaced with a design to fail structure and culvert. The next flood will look like this again.
Or we can move diversion points when given the opportunity. Its easy to think this type of flood will not happen again. We do not know when the next fire or flood will happen. Or microburst of water focused on one watershed.
Resilience planning starts before the fire and flood.
Resilience conversations start before the fire and flood (repeated for emphasis). These are difficult conversations. We need to have them before the next fire and flood. We need to talk with our communities about the changing flood risk.
We need to have difficult conversations with people. Human to human.
Photo Credit to the Watershed Center https://watershed.center/ (formerly Lefthand Watershed Oversight Group)
Challenges using rain on grid modeling in the mountains of Colorado
Reach out if you would like to hear this presentation. We can schedule a time.
Trauma and Recovery
This is a paper I worked with a trauma therapist to create for people affected by floods and the flood recovery work. I saw many trauma reactions when working with stakeholders after the 2013 Front Range floods. There are simple treatments that a therapist with training can help with. I do not want to recommend specific treatments because I am not licensed and not up to date a specific treatments as they evolve.
Chaffe County Land Use Code Changes – Proposal for Riparian Protection
A primer on Fluvial Hazard Zone Mapping with LiDAR data
The is a very technical post. This is a primer to discuss how LiDAR data is collected, filtered and manipulated to create digital elevation models (DEM) and how those DEMs might be used to identify fluvial geomorphic signatures that indicate where a flood hazard might exist. LiDAR data is commonly used in geomorphic analysis, hydraulic analysis and floodplain mapping. In order to use the data effectively the user needs to understand the limitations of the data.
February 18, 2023 NRCS Data collection and Snow Water Equivalent
The Snow Water Equivalent (SWE) is not as optimistic as some would hope. Below is a screen shot taken from the NRCS interactive website. The color-coded points are the locations the SWE is measured. The percent value is compared with the peak based on the median peak which is calculated for the period of record.
The period of record minimum (when they started recording data) is shown below which varies from 1977 to 2005.
The period of record for the maximum is shown below. If the color of the dot changes than they are no longer collecting the peak data. It looks like a lot of sites are no longer being collected.
