On October 23, 2018, the President signed Senate Bill No. 3021, America’s Water Infrastructure Act of 2018, into law (Public Law 115-270).  The law, also known as the Water Resources Development Act (WRDA) of 2018, includes some interesting provisions that I will highlight in this post.

The Sense of Congress

The first provision reaffirms that Congress would like to pass a water resources development bill each time they meet. The first WRDA was passed in 1974 and in the 1980’s and 1990’s new legislation was passed almost every two years.  Between 2000 and 2014 the pace of reauthorizations slowed. The passage of the 2018 reauthorization sets Congress back on the every-two-years pace, with bills passed in 2014, 2016, and 2018.

Move Civil Works to Another Agency?

The law requires the U.S. Army Corps of Engineers (USACE) to hire the National Academy of Sciences to conduct a two-year study on:

The ability of the Corps of Engineers to carry out its statutory missions and responsibilities, and the potential effects of transferring the functions (including regulatory obligations), personnel, assets, and civilian staff responsibilities of the Secretary relating to civil works from the Department of Defense to a new or existing agency or subagency of the Federal Government, including how such a transfer might affect the Federal Government’s ability to meet the current statutory missions and responsibilities of the Corps of Engineers; and,

Improving the Corps of Engineers’ project delivery processes, including recommendations for such improvements, taking into account factors including: the effect of the annual appropriations process on the ability of the Corps of Engineers to efficiently secure and carry out contracts for water resources development projects and perform regulatory obligations; the effect that the current Corps of Engineers leadership and geographic structure at the division and district levels has on its ability to carry out its missions in a cost-effective manner; and the effect of the frequency of rotations of senior leaders of the Corps of Engineers and how such frequency affects the function of the district.

Economic Analysis Methods

The statute also requires the USACE to hire the National Academy of Sciences also to:

carry out a study on the economic principles and analytical methodologies currently used by or applied to the Corps of Engineers to formulate, evaluate, and budget for water resources development projects; and, make recommendations to Congress on potential changes to such principles and methodologies to improve transparency, return on Federal investment, cost savings, and prioritization, in the formulation, evaluation, and budgeting of such projects.

Transparency and Stakeholder Engagement

The law requires USACE to enhance transparency and information exchange. The USACE must issue project proposal guidance for non-Federal project sponsors, assist non-Federal interests with researching and identifying USACE project authorizations and decision-making documents. The law also strengthens stakeholder engagement.

Texas Projects

As for projects in Texas, the law:

• Authorizes a navigation feasibility study of the Trinity River and Tributaries near Liberty, Texas, as defined in the USACE 2017 and 2018 reports to Congress;
• Authorizes a flood risk management feasibility study associated with West Cell Levee, Irving, Texas, as defined in the USACE 2017 and 2018 reports to Congress;
• Directs the USACE to “expedite the completion of studies for flood damage reduction, hurricane and storm damage reduction, and ecosystem restoration in the coastal areas of Texas that are identified in the interim report due to be published in 2018 that describes the tentatively selected plan developed in accordance with section 4091 of the Water Resources Development Act of 2007;”
• Directs USACE to prepare a report on the status of the implementation of a water supply contract at Wright Patman Lake, Texas; and,
• Directs USACE to “expeditiously carry out any project for flood risk management or hurricane and storm damage risk reduction authorized as of the date of enactment of this Act to be carried out by the Secretary in Texas, Florida, Georgia, Louisiana, South Carolina, the Commonwealth of Puerto Rico, or the United States Virgin Islands.”

Please note that “authorizations” in federal law, just provide direction and permission to take action, but without any funding.  In federal water resources programs, Congress must then decide to “appropriate” funding to actually complete authorized projects.

Did you notice anything interesting in this year’s WRDA? Leave a comment if you did.

Oh, and Happy Halloween!

Someone recently asked me if I could estimate the financial impacts to the Houston area from the release of Atlas 14, Volume 11, Version 2.0. The short answer is no, but I can write a blog post with a rough qualitative and directional assessment of impacts!

Flood damage reduction infrastructure will need to be bigger to achieve the 1% annual chance risk level we have generally settled upon. This will mean that pipes or structures that carry the runoff that is generated from the 1% annual chance, 24-hour rainfall will be larger. Thankfully pipes, culverts, and earthen ditches don’t increase in cost linearly with their carrying capacity, but they do tend to get more pricey as they get bigger.

As you drive around the Houston/Harris County region you might sometimes notice concrete “notches” in the banks of some of the bayous or “flumes” that connect the bayou to a detention basin.  You might also see the same type of structure in smaller detention basins in and around neighborhoods.  Those structures allow the runoff from larger storm events to flow to or from the bayou and the channel with less chance of erosional damage.  Because they often are designed to carry the runoff from larger storms, they will be larger if they are designed to carry the flow arising from the updated rainfall stats. Here’s a screenshot of one of these structures from Google Maps:

Pipes that carry smaller storms may not increase in size that much or at all, because the Atlas 14 information did not change the smaller, more frequent rain event depths that much. For example, the 50% annual chance, 24-hour event reported for the center of Harris County near Houston in “Technical Paper No. 40: Rainfall Frequency Atlas of the United States, For Durations From 30 Minutes to 24 Hours and Return Periods from 1 to 100 Years” (affectionately known as “TP-40”) (1961) is somewhere in the 5.1 to 5.2 range on the national scale map (screenshot below) and the same event in Atlas 14 is reported as 5.11 inches; so they are pretty close.  This means that the smaller neighborhood storm sewer pipes that are designed to carry runoff from these frequent, smaller events, might be able to stay the same size and, therefore, cost about the same.

One of my co-workers evaluated a hypothetical 160-acre green-field development site to see if detention ponds would need to be larger as a result of the initial draft release of Atlas 14, using a storm event depth of 17.7 inches in 24 hours. The evaluation showed that both the pre-development and the post-development flows increase, so the difference was not large enough to exceed the applicable regulatory minimum detention rates of 0.50 acre-feet or 0.65 acre-feet (Houston and Harris County). The results of this evaluation are shown below.

This suggests that most detention basins will still be sized to provide between 0.5 and 0.65 acre-feet per acre of development because most local governments won’t let folks install smaller ones.  This will have to be evaluated for more sites to be sure, but that’s what we saw for the one site we evaluated.

Regulatory floodplains will be remapped over the next three to four years using the more accurate rainfall depths. Harris County Flood Control District is already moving forward with this work.  This will enlarge them and more existing structures will then be located in the regulatory floodplain. This will increase the cost of insurance premiums to obtain coverage for many buildings and facilities. Approximately 37% of the county is inside one of the regulatory floodplains defined by the National Flood Insurance Program (NFIP). These include areas that have greater than a 1% annual chance riverine flooding, greater than 0.2% annual chance of riverine flooding, or greater than a 1% annual chance of coastal flooding.  The updated rainfall data will increase the area of the county that is in a regulatory floodplain by some amount.

Based on the elements above, it appears that the financial impact of the publication of the rainfall statistics update will be less significant than the financial impact of the floodplain map updates coming in a few years.

If you have other thoughts about cost or financial impacts, please leave a comment.

On September 27, 2018 Version 2.0 of the National Oceanic and Atmospheric Administration’s Atlas 14, Volume 11 was released and a press conference was held. As I’ve described in previous posts, Volume 11 provides us with a more accurate picture of the annual probability of rainfall of various depths and durations across the state of Texas.  These data were last updated across the entire state in 1961.  Volume 11 was created by evaluating rainfall records as early as the 1870’s up through 2017.

As I written previously, the depth of 1% annual chance, 24-hour rainfall is a key design storm we use for drainage and flood risk reduction infrastructure in the Harris County area.  Prior to Volume 11, this key design storm was about 12.4-inches in western Harris County and about 13.5-inches in southeastern Harris County, as shown below.

After Volume 11’s release the new 1% annual chance, 24-hour duration rainfall map for Harris County looks like this:

We used to believe that the 1% annual chance, 24-hour storm was 2.6-inches to 4.5-inches smaller than it actually is. This was because the rainfall records did not span as long a period as they do now. Our uncertainty bands have gotten a bit narrower and the overall magnitude of most storm frequencies and durations have increased.  The actual depth of the 100-year, 24-hour duration rainfall ranges from 21% to 33% higher than we thought.

The updated information is presented by NOAA using a web-based map interface, located here: https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_map_cont.html. It allows anyone to double click on the map at any point of interest and instantly get both a tabular and graphical display of the rainfall stats.

Here’s how it works for my neighborhood in west Houston.

This first image is from the map interface. I have zoomed into my part of town and have double-clicked on the map near my house. The red cross-hairs show the click point.

After double-clicking the following information appears below the map:

This shows that my house has a 1% annual chance of receiving 16.5 inches (or more) of rain in 24-hours.  If you read the fine print you will see that there is a 90% chance that the actual rainfall depth for this 1% annual chance, 24-hour storm ranges will be somewhere between 11.6 inches and 23.5 inches, because of the uncertainty of our statistical estimate.  The website also provides a graphic version of the same data:

The website also provides a graph that illustrates the confidence bands around the estimated rainfall depth. The figure below shows confidence range for all 24-hour storms.  The green line shows the upper limit of the 24-hour rainfall depth and the red line shows the lower limit. There is 90% chance that the “true” rainfall depth will fall in between those values (for any given recurrence interval).  Please recall that “recurrence interval” is the inverse of annual probability.  So the 1,000-year storm has a 1/1,000% chance of occurring in any given year.  If you convert the fraction to a decimal, that’s a 0.001% annual chance. Notice how that is not zero?

See how the confidence range grows for the larger, more rare events?  The 100-year recurrence interval corresponds to the 1% annual chance event. The math tells us that there is 90% chance that the 1% annual chance, 24-hour event is somewhere between 11.6 inches and 23.5 inches. The corollary is there is 10% chance that the real depth is outside that range.

The expanding confidence interval – the gap between the green line and red line – makes sense because we have statistically evaluated rainfall records that only go back to, at best the 1870s, and, at worst 1970’s.  This is a period of record of only between 47 and 148 years.  So our certainty about 500-year or 1,000-year recurrence interval events is low.

In my next post I will be providing some thoughts about the cost impacts of this refined view of our rainfall statistics.