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Archive for the ‘watershed analysis’ Category

Back in the 1970’s and 1980’s, the U.S. Army Corps of Engineers had the foresight to know the value inherent in floodplains. Consequently, over the course of several years, this agency went about purchasing floodplain land in the Charles River watershed. The Army Corps coined the term “Natural Valley Storage Areas” (NVSA’s) which is indeed what intact and functional floodplains do. The homepage for this project can be viewed here.

Fast forward to 2017 to when the Army Corps presented their Draft Master Plan for the project to the public. The Corps conducted an economic analysis of the benefits of these storage areas. The estimated prevented losses from flood damages was almost $12 million in unadjusted dollars. The Corps also estimated the economic benefits of visitors and recreation between $3.2 an $4.6 million.  Based on this analysis, one could say the natural capital in these areas protected areas is at least $15 million.

At the public meeting,  the Army Corps presented the hydrograph for the 2010 floods in late March and early April. As soon as I saw the data, I was reminded of the Otter Creek analysis I had written about.  My only problem with the analysis that the Army Corps presented, was that the discharge was not normalized by drainage area.  After obtaining the data from the gauges in Dover, MA and  Medway, MA, the story appeared to be pretty similar to Otter Creek’s.

The data show that for the upstream gauge in Medway, the peak unit discharge was 26.8 cubic feet per second (cfs) per square mile (csm) on March 31, 2010. Note how much more rapid the rising limb of the Medway unit hydrograph is compared to the Dover gauge.  On April 1st and 2nd the Medway runoff is receding, whereas the Dover runoff is still increasing, albeit at a slow rate.  The peak discharge in Dover occurs on April 2nd, but only at a unit runoff of only 15 csm.  Just as with the Otter Creek analysis, we can do a ‘what if’ analysis and simply assume that Dover had very similar unit runoff as Medway. Under this hypothetical scenario, Dover could have experienced a discharge of just over 4,900 cfs (26.8 csm X 183 square miles).  Fortunately, the peak mean daily discharge at the Dover gauge was 2,760 cfs, which is 56% of the theoretical peak, had the same unit runoff occurred throughout the watershed.  The two USGS gauges and the Natural Valley Storage Areas can be seen in this ArcGIS Online presentation slide.

A cursory review of the NVSA’s indicate that while floodwaters can and indeed are stored, it would be perhaps a bit too generous to attribute all of the flood attenuation between Medway and Dover to these areas. The 8,095 acres of storage area converts to 12.6 square miles, or roughly 6.9% of the Dover gauge’s watershed area.  In addition, at only 65 square miles, one would expect a certain amount of flashiness (i.e. rapidly increasing and decreasing flows) at the Medford gauge.  Nevertheless, as a thought experiment,  had the Natural Valley  Storage Areas been developed and the percent impervious area dramatically increased in these areas, one could safely assume that  the Dover gauge would very likely have seen a unit discharge higher than 15 csm.  The NVSA’s do provide important floodwater storage and the Army Corps analysis does indeed indicate a diminution in flood damages.

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ESRI has created it’s own social network for user’s of its software called GeoNet. Back in March, ESRI created a webinar titled “Community Maps for Hydrology” and can be viewed here. The entire video is 53 minutes. Viewers might want to fast forward to about the 22 minute mark where the speaker starts to talk about and demonstrate the watershed delineation and downstream trace tools.  If you have points on a stream in a watershed, it is a fairly straightforward affair to delineate a watershed in either ArcMap or ArcGIS Online.  The appeal to doing this workflow in ArcMap is that if the delineated watershed is in a geodatabase, it is easy to get an area straight from the attribute table.   The video also discusses maps that provide real-time stream gage data and how it is possible to get a hydrograph plotted just below the map.

ESRI has also updated Maps for Office to version 3.  The interface is a bit more modern. As for new functionality, I think one of the biggest additions is that users can have more than one map displayed for a given tab.  ESRI’s blog post on the update is available here.

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The USGS has reviewed several gauges throughout the state and has now developed regional bankfull geometry curves.  For those of us waiting for these data so that we can put them to use on projects, this is a great development.  The study does have a few geographic limitations, so take note of those caveats before putting the equations to use.
http://pubs.usgs.gov/sir/2013/5155/

 

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The good news is that ESRI is offering a quick and easy way for users to delineate watersheds using one of its online services in ArcGIS online. You can read about here:
http://blogs.esri.com/esri/arcgis/2013/08/13/custom-watersheds-at-the-click-of-a-button-watershed-delineation-in-arcgis-online/

The one downside is that the service is only available to users who have an ArcGIS organization account. An alternative is the functionality that is available in HydroDesktop (http://his.cuahsi.org/hydrodesktop.html). This software relies on an EPA service that for the most part works pretty well, but I’ve experienced some erroneous results from time to time when making a delineation. The upside is that the software will create a shapefile of your watershed of interest to you local disk which can be convenient.

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The Washington Department of Fish & Wildlife has just released a draft of its document titled “Stream Habitat Restoration Guidelines 2012” here.  It’s an  831 page document that I’ve only skimmed so far.  It does look rather thorough and as with many other documents covering the subject in general, it advocates for a watershed analysis and perspective on impacts throughout the landscape that can have an effect on physical channel habitat.  The document has 5 chapters covering some broad restoration themes, it then goes into 13 specific restoration techniques ranging from floodplain and channel manipulation, to large woody debris management and beaver management.  Finally, the document provides 10 appendices which appear to be introductions to academic courses such as fluvial geomorphology, sediment transport and hydrology.  Overall, it looks like an excellent reference to add to one’s  library on the topic of stream restoration.

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I just received this email and as a Utah State alum, I thought it was worth posting:

—————————————————————————————————

August 6-10, 2012
Intermountain Center for River Rehabilitation & Restoration
Utah State University
Logan, Utah

For more information and registration: http://cnr.usu.edu/icrrr/

This course is for those who wish to understand and apply the principles of sediment transport to alluvial channel assessment and design.  Principles of open channel flow and sediment transport are combined with watershed hydrologic and sediment source analysis to place channel assessment and design in the appropriate context. The course balances advance reading, lecture, field work, and hands-on exercises for estimating sediment supply, calculating sediment transport rates, forecasting channel response to water and sediment supply, and a class project incorporating gravel augmentation into channel design for dynamic fish habitat.  This course is intended for participants who are familiar with basic principles of river geomorphology.

Topics include:

  • Spatial analysis tools for estimating sediment supply at the watershed to reach level
  • Threshold and alluvial channel models, with guidelines for assessment and design incorporating uncertainty
  • Sediment transport calculations: challenges and methods, sediment rating curves, cumulative transport
  • Field measurement of sediment transport and guidance for different sampling approaches
  • 1-d flow and transport models: HEC-RAS applied to flow competence and sediment transport capacity
  • Forward and inverse application of mixed-size surface-based transport models

Principal Instructors

Peter Wilcock (course director), Professor, Geography and Environmental Engineering,
Johns Hopkins University

Tyler Allred, Principal, Allred Restoration

Patrick Belmont, Professor, Watershed Science, Utah State University

Susannah Erwin, Postdoctoral Associate, Watershed Science, Utah State University

Milada Majerova, Postdoctoral Associate, Watershed Science, Utah State University

The course is taught among the majestic peaks of the Wasatch and Bear River mountains near Logan UT. Cache Valley is a delightful place to visit in August.  Salt Lake City is easy to fly into and there are abundant opportunities for outdoor adventure before & after the course.

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Last October, the National Fisheries Service has released a report titled “Science Base and Tools for Evaluating Stream Engineering, Management, and Restoration Proposals.”

http://www.nwfsc.noaa.gov/assets/25/7946_01092012_143328_RiverRatTM112WebFinal.pdf

The tools in the report include a project screening matrix, an information checklist and information on the River Restoration Analysis Tool (RiverRAT).  The screening tool and information checklist are straightforward.  Roughly seventy pages of the report cover fluvial geomorphology (yay!) and stream habitat. The fourth section of the document covers various aspect of a project as is progresses along.

The report also has four extensive appendices:

A) Investigative Analyses
B) Design of Stream Channel and Streambanks
C) Management Alternatives
D) Bibliography

For those familiar with the literature, much of the material will be review. Nevertheless, the overall document is a well organized compilation of available tools and the steps that should be taken as part of a restoration project.

HT: Peter Skidmore’s post in the LinkedIn group River Restoration Northwest

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