Guest Editorial
Message from the President
Message from the Executive Director
New Member Welcome
Know Your AIH Peers
Call for Executive Committee Nominations
Oregon Chapter Participates in Water Resources Symposium
Technical Papers
      Bulletin 17C: Updated Federal Guidelines for Flood Frequency Analysis
      International Stormwater BMP Database
      Equations for NRCS Unit Hydrograph
Treasurer’s Statement of AIH’s Financial Condition
Obituary: Robert Lee Vincent


Guest Editorial – Water Resources: Science, Security, and Sustainability
Roman Kanivetsky, Department of Bioproducts and Biosystems Engineering, University of Minnesota, St. Paul, Minnesota 55108

Our planet is rapidly changing and this requires a radical rethink by all of us. A changing planet requires a transformation towards a new paradigm in which convergence of biophysical, social, economic and governance systems takes place. Water resources security and sustainability is a daunting challenge for academia, government and private sector. A recent paper (James & Shafiee-Jood, 2017), suggesting this new paradigm, calls for an interdisciplinary information platform to incorporate science and knowledge in order to achieve both water security and sustainability. Such a platform would encompass interdisciplinary monitoring of parameters in hydrologic, engineering, economic, financial, environmental, social, political and legal areas by establishing observatories that record time series of data on variables from all eight dimensions. While this paper recognizes that the greatest challenge to find solution is deeper understanding of interaction between all systems and is presenting a comprehensive information platform for water resources management, I argue that this platform alone is not enough to address water security and sustainability. What is missing from this approach is the role of science and knowledge.

Science and Knowledge

In recent years, there has been a dangerously overoptimistic picture that advances in digital technology, artificial intelligence, and other technological innovations may provide solution to complex problem of water security and sustainability. Such mind-set may lead to biasing decision by policy makers and solid opportunities maybe dismissed. As a result, the science and knowledge are relegated to the side wings if not thrown out altogether. At the same time, efforts to make progress in addressing water security and sustainability were increasingly being stalled by lack of knowledge and science rather than the weakness of political will.

To overcome these challenges and harness opportunities, hydrologists must shift their thinking in how they characterize the hydrologic system. That is, the system structures should be defined such that all components of the terrestrial hydrologic system are unified. This can be achieved through a system theory model as opposed to a traditional model. The application of system theory model was created by the team at the University of Minnesota (Peterson, Nieber, Kanivetsky, & Shmagin, 2013).

Water Security

Another important issue in water resources management is to clearly define what is the ultimate goal of the program? Is it water security or water sustainability? The concept of water security has received increased attention over the past decade, in both policy and academic debates. For example, UNESCO definition of water security is to protect vulnerable water systems, mitigate the impacts of water-related hazards such as floods and droughts, safeguard access to water functions and services and manage water resources in an integrated and equitable manner” (UNESCO – IHE, 2009). While this paper does not provide a comprehensive analysis of this concept, it is important to acknowledge that the concept of water security is not operational or conceptual in nature. Instead, it is confusing and misleading. More importantly, it does not include long term thinking and concern for future generations. In contrast, the concept of water sustainability does incorporate a “long-term” view, where concern for future generations is central to the definition (Meadows, Meadows, & Randers, 1992). In other word, sustainable development cannot be achieved without sustainable water supply. Thus to bring clarity to debate in the academic community, scientists argue the need to abandon the term water security and instead use water sustainability. The interdisciplinary information platform proposed by James and Shafiee-Jood (2017) would guide this transition if refocused to include sustainability instead of water security.  

Water Sustainability

The last half century has seen a number of transitions in how society views the relationships among environment, development and knowledge (Clark, Crutzen, & Schellnhuber, 2005). Sustainability challenges pose the question whether we can hope to see the current level of well-being at least maintained for future generations, or whether the most likely scenario is that it will decline. It is no longer a question of measuring the present, but rather it is about forecasting the future. This prospective dimension multiplies to enormous difficulties and deserves separate measurement in stricto sensu (Stiglitz et al., 2010). Only very recently, however, has it become evident that the Anthropocene crisis forces humanity to manage consciously and transition toward sustainable use of Earth’s resources, especially water. As a result, it has become widely recognized that such a transition can be achieved only through knowledge-based activity.

This new field of knowledge called “sustainability science” emerged in the first decade of the 21st century and focuses on the interaction between nature and society with equal attention as to how society changes environment and how environment changes society (Clark, 2007). The key characteristics of a sustainability science approach are: a) problem-driven (Stokes, 1997), b) focus on the interaction between nature and society, using the framework of complex ecological, economic, social and governance systems, c) spanning the range of spatial scale from local to global, and d) addresses long term issue of future generations.

Sustainability science uses a systems modeling approach where human-environmental systems are defined as complex, heterogeneous, non-linear, spatially nested and hierarchically structured. Thus, to develop knowledge for water sustainability utilizing information system proposed by James and Shafiee-Jood (2017) the critical next phase is to develop a unified system model for convergence of hydrologic, economic, social, and governance systems. Key to this idea of convergence is that ideas, theories, approaches, and technologies from widely diverse fields of knowledge are merged, or integrated. In turn, this is one useful strategy for solving complex problems and addressing complex intellectual questions underlying sustainability science.

To transition from knowledge of water availability to action, this biophysical limit will guide the development of a new economic model that addresses the value of water. – be it monetary or non-monetary on biophysical metrics of water and then a need to change and create new social logic and social system rooted in this new economic model that recognizes the limit of biophysical system of water resources. To achieve this integration requires discovery of the structures for economic, social, and governance systems, similar to what has been defined for hydrologic systems, with subsequent convergence of the knowledge to address water sustainability. The information system proposed by James and Shafiee-Jood (2017) can serve as a foundation for such convergence. However, the “knowing” notion is not enough. Instead, we must shift our thinking toward “learning”, simply because we have so much to learn. Trying to discover or write blueprints for such turbulent, rapidly evolving systems will in many cases prove futile. More important is that we recognize the extent of our ignorance, accept the concomitant necessity to treat policies and other management interventions as experiments, and take measures for learning from, the experiments we are forced to conduct on ourselves. Sustainable water resources management thus becomes viewed as a process of adaptive management and social learning in which science and knowledge plays a central role.

What will take us there?

Under the leadership of AIH, the hydrologic community should move forward to define the challenge of water resources sustainability and start the conversation for how to solve the problem and incorporate opportunities to “learn” integration first-hand. Understanding hydrologic systems alone is not enough. Instead, we as hydrologists need to develop a mechanism for collaboration with experts in economic, social, and governance fields to create the unified model for convergence of all these systems. Unfortunately, at present time the hydrologic community is completely oblivious to “sustainability science” paradigm. Another barrier is that institutional structure of academic enterprise is not set up to support this kind of work.  It is hoped this essay will launch such conversation.


Clark, W. C. (2007). Sustainability Science: A room of its own. Proceedings of the National Academy of Sciences of the United States of America104(6),1737-1738. 10.1073/pnas.0611291104

Clark, W. C., Crutzen, P. J., & Schellnhuber, H. J. (2005). Science for Global

Sustainability: Toward a New Paradigm. KSG Working Paper No. RWP056-032.

Cook, C. & Bakker, K. (2012). Water security: Debating an emerging paradigm. Global Environmental Change, 22, 94–102.

James, L. D. & Shafiee-Jood, M. (2017). Interdisciplinary information for achieving water security. Water Security, 2, 19-31.

Meadows, D.H., Meadows, D.L. & Randers, J. (1992). Beyond the Limits: Global Collapse or a Sustainable Future. London: Earthscan Publications Ltd.

Peterson, H. M., Nieber, J. L., Kanivetsky, R. & Shmagin, B. (2013). Regionalization of landscape characteristics to map hydrologic variables, Journal of Hydroinformatics, 16(3), 633-648,

Stiglitz, J. E., Sen, A. & Fitoussi, J. P. 2010. Mis-measuring Our Lives: Why GDP Doesn’t Add Up. New York: The New Press.

Stokes, D. 1997. Pasteur’s Quadrant: Basic Science and Technological Innovation. Washington, D.C.: Brookings Institution.

UNESCO – IHE. (2009). Research Themes: Water, Food & Energy Security. Retrieved from


Message from the President

John Nieber, P.H., P.E., Ph.D. – AIH President

Dear AIH Members:

As the new president of AIH, just starting a two-year tenure in the office, I send my hopes that you have all started off the new year well. You all heard from Rao Govindaraju in the last quarterly newsletter that he would be stepping down as president with the new year and taking on the position of past-president. In November Jamil Ibrahim was elected to become president-elect and he will serve in that position for two years. Jamil had been Vice President for Institute Development, and in his place Julé Rizzardo was elected by the membership to take that position over the Institute Development position. Jolyne Lea took the position of Secretary after Marc Horstmann recently stepped down. We wish to thank Marc for his service to AIH.

This year, AIH is embarking on a number of key initiatives. One major initiative led by Faisal Hossain, our Vice President of Academic Affairs, has been to move the AIH certification exams to digital media so it will be possible for examinees to take exams online. A large part of this effort has been to translate exam questions to digital form. We also want to update questions, so a detailed review of the existing exam question database has been undertaken with some questions being eliminated, some questions being rewritten and some new ones added. With regard to exam questions we wish to take advantage of the diverse expertise of the AIH membership and ask members to submit questions that could be employed in the exams. A request to the membership to submit questions is included in this newsletter. 

A second major initiative, also led by Faisal, has been to develop the framework for AIH to offer webinars to AIH members and eventually to non-members as well. The plan for 2019 is to have three webinars, with the first two to be presented by Dr. David Williams. These webinars will be offered free to AIH members. In the future we hope to be able to offer webinars at a cost to non-AIH members as well.

A third major initiative, led by Jamil, has been to review and revise the bylaws of the Institute. We have found this effort to be a monumental task and progress has been incremental with the effort being applied to one article of the bylaws at a time. The Institute intends to hire legal assistance to verify that the revised bylaws will provide clear guidance to promote smooth functioning of the Institute.

The Institute has an excellent group of hard-working members serving on the Executive Committee. Together they constitute a dynamic group of progressive professionals, ready and active to develop and lead the Institute. To keep the momentum, it is essential to keep the positions of the Executive committee filled with enthusiastic and dedicated professionals. Within the year we will have two positions become vacant. Greg Bevenger, the current Treasurer, has given us notice that he will resign the position by the end of 2019. Likewise, Faisal Hossain, the current Vice President for Academic Affairs, has also requested to be replaced within the year because he will be going on sabbatical leave. We will be seeking nominations for both of these positions later this year. Both Greg and Faisal have been very effective in moving the Institute forward and we hope to be able to recruit nominees who will be equally effective. You should expect to hear from us through Institute communications regarding requests for nominations.

With this message I wish you a very productive spring. As Rao mentioned in the last newsletter, please do send us your stories relating to your professional work in hydrology. 

Warm regards,

John L. Nieber, P.H., P.E., Ph.D.
Department of Bioproducts and Biosystems Engineering
University of Minnesota
1390 Eckles Ave.
St. Paul, MN 55108


Message from the Executive Director

Nicole A. Singleton, MBA, MA – AIH Executive Director


Dear AIH Members,

As the Executive Director of the Institute, we are excited to see the continuous growth and engagement of our organization and its members.  Notable accomplishment by AIH in 2018 include:

  • AIH boasted an increase in membership of 31% increase over 2017;
  • We beta-tested our first ever online certification exam process;
  • We exhibited at allied industry conferences;
  • We significantly increased our communication efforts with an active social media presence, bi-annual news bulletin, and association-specific email campaigns.

Thank you for your continuous involvement.  We would not have been able to accomplish such feats without your support.

Likewise, we are enthused for what is in store for 2019.  Each of our committee members and the management office have established strategic goals, which will enable us to continue to deliver upon the established, AIH mission and objectives.  Look for increased professional development and networking opportunities in this coming year.  Additionally, we will continue to update our exams and migrate our certification application submission and exam process to an online format.

If you have not done so already, please take a moment to visit the AIH website and join us in conversations on AIH social media pages.  We also look forward to celebrating your exciting accomplishments, industry awards, and celebrations.  Be sure to email this information and photos to us.

As always, our management office stands ready to support and assist AIH members.  We welcome the opportunity to hear from you.  Give us a call at 303-339-0523 or send us an email.


Nicole A. Singleton, MBA, MA


New Member Welcome

AIH welcomes the following individuals to AIH, admitted under various membership categories between September 1, 2018 and March 31, 2019.





Andrew Walker


Weston + Sampson

Newmarket, NH

Bill W Woessner


Woessner Hydrologic LLC

Missoula, MT

Luciana K Cunha


WEST Consultants Inc.

Folsom, CA

Michael Lozzi


Georgia State University

Houston, TX

Thomas E Nordstrand


Adams State University

Albuquerque, NM



Know Your AIH Peers

In this issue of ‘Know Your AIH Peers’, we present a new member’s perspective of AIH and the profession of hydrology. Luciana Cunha, Project Manager with WEST Consultants, Folsom, CA ((319) 541-7050)) is a new AIH member certified last year. The interview was conducted by Julé Rizzardo, AIH Vice President for Institute Development.

Q:  What is one thing you’d most like to get out of your AIH membership?

Networking.  I’d like to get to know more people in the area outside of work.  As engineers, we tend to work on computers and projects and it can be a little isolating.  There is a huge need to chat with other people informally to share personal experiences, learn things, and network.

Q: Describe the work project or team you had the most fun with?

There are so many projects, it’s hard to just pick one.  But my work on the Desert Hydrology Manual was really interesting.  We updated a manual that was published 23 years ago, so it involved analyzing a suite of hydrologic methods, including detailed flood-frequency analysis, regional regression equations and rainfall-runoff simulation. 

Q: What’s your favorite thing to do on a day off work?

I enjoy going to the gym, hanging out with friends, or taking my dog to the park.  Living in Sacramento, there are so many fun day trips you can take to places like Napa, Tahoe and San Francisco.  I also love snowboarding and going to the mountains whenever I get a chance. 

Q:  What do you find most challenging about hydrology?

Uncertainty.  It’s different than hydraulics and it’s more deterministic, so it requires that you learn how to work with it.  The natural variability is a huge challenge.

Q: What’s your favorite hydrologic feature to visit?

Iguacú Falls.  It’s one of the seven Natural Wonders of the World, and is actually made up of more than 270 falls located in Brazil and Argentina.

 Q:  AIH is planning to roll out some new member features, including an online member directory to allow members to connect with others, and a social mixer event here in Sacramento.  What do you think?

That sounds great, especially if it were open to non-members as well as members.  For professionals who are not part of AIH already, it would be helpful to talk to members about the process of getting registered. I look forward to networking with more with professionals in the Sacramento area.



Call for AIH Executive Committee Nominations

The American Institute of Hydrology is calling for nominations for two positions on its Executive Committee. The organization seeks candidates for two positions: 1) Treasurer and 2) Vice President for Academic Affairs. The current members holding this position have indicated they will not be seeking re-election.

The Treasurer will work with the AIH Executive Director to submit to the Executive Committee an annual budget and an annual financial report, secure audits of Institute financial records, work with the management office to prepare and file all documents required by the Internal Revenue Service and other state and federal agencies, actively seek gifts and grants for the Institute, and generally managefinancial affairs and resources of the Institute as directed by the Executive Committee.

The Vice President for Academic Affairs is responsible for the certification program of the Institute, reviews committee membership and examination goals, establishes and maintains a network of examiners, and oversees student membership.

The terms for both positions will begin on January 1, 2020. The term of the elected positions is for four years.

AIH invites and encourages its members to consider applying for this position. Please submit your nomination. In your submission, please include a statement of interest (maximum 150 words) and a professional biography (maximum 150 words).



Oregon Chapter Participates in Water Resources Symposium

The Oregon Chapter of AIH was a proud sponsor of the 9th Annual Pacific Northwest Water Research Symposium organized by the Oregon State University hydrology student group “Hydrophiles” on  April 8-9th 2019 at the OSU campus in the CH2M Hill Alumni Center in Corvallis, Oregon. This annual event supports students participating and presenting water resource related research.  Oregon Chapter President Jolyne Lea, Vice President Rich Marvin, and Treasurer/ Secretary Kyle Dittmer attended the event.


As part of our sponsorship, the Oregon Chapter of AIH had a booth and participated in the two-day, student-centric conference highlighting outstanding student research in the fields of water resources science, engineering, and policy.

This symposium bought students from Oregon, Washington, Idaho, and beyond to present their proposed, ongoing, or completed research.  Current graduate and undergraduate students conducting freshwater-related research in any field (science, policy, engineering, etc.) provided both oral and poster presentations. Oregon AIH members attended networking sessions and talked with students at the booth, providing information about AIH certification and our perspective on working as professional Hydrologists.  The Symposium provided an invaluable opportunity for the exchange of ideas among students, university faculty, professionals working in water resources, and the surrounding community.



Technical Papers

Bulletin 17C: Updated Federal Guidelines for Flood Frequency Analysis

Authors (with affiliations):

  • Julie E. Kiang (USGS), Robert R. Mason (USGS), John F. England (USACE), Beth A. Faber (USACE), Jery R. Stedinger (Cornell University), Wilbert O. Thomas (Michael Baker International), and Andrea G. Veilleux (USGS)

Key points: New guidelines for flood-frequency analyses in support of Federal projects have been published.  The new guidelines are based on improved statistical procedures developed since the last update was published as Bulletin 17B in 1982.  Improvements include use of interval data to represent floods that would likely have been individually noted in historic or paleoflood information had they occurred and had they exceeded the interval; an improved “method of moments” for fitting the flood data to the log-Pearson Type III distribution; a test that identifies multiple potentially influential low flood peaks; new techniques for estimating the regional skew of flood distributions; and more reliable confidence interval estimates.  The new guidelines do not directly address nonstationarity or climate change.

Floods are dangerous natural hazards that can threaten lives, livelihoods, and property. Flood risk computations supply quantitative information needed for the planning, design, and management of infrastructure along rivers. Flood frequency analysis provides information about the magnitude and frequency of flood discharges and is used to estimate the probability of flooding at specific river locations. These analyses are generally based on records of annual maximum instantaneous peak discharges collected at stream gages and often supplemented with nonsystematic information, such as knowledge of historical floods and regional flood experience.

To ensure consistency in flood frequency analysis, federal agencies, university researchers, and engineering consultants worked together through the auspices of the Advisory Committee on Water Information ( and its Subcommittee on Hydrology to produce updated procedures that were then published by the U.S. Geological Survey. Released in 2018, the new guidelines are titled: Guidelines for Determining Flood Flow Frequency, Bulletin 17C ( (England et al., 2018). The new guidelines are based on improved statistical procedures developed since the last update was published as Bulletin 17B in 1982.

The Bulletin 17C guidelines retain the basic statistical framework used previously to ensure consistency with previous flood-frequency studies. The guidelines also incorporate the following advances:

  • A more generalized representation of flood data is used, allowing description of flood peaks as intervals (that is, a range) rather than as a point value (that is, a single value).  The use of flood intervals allows a more robust representation of imprecise flood information, such as that available from historical records or paleoflood data.
  • The Expected Moments Algorithm (EMA) is adopted as an improved method for fitting the Log-Pearson Type III distribution to flood peaks. The EMA method is able to represent floods as intervals.
  • The Grubbs Beck test used in Bulletin 17B was generalized to test for multiple potentially influential low floods (PILFs) using the Multiple Grubbs Beck Test (MGBT). The MGBT test identifies the PILFs for special treatment which limits their impact in a flood frequency analysis.
  • New methods for estimating regional skew and its uncertainty are presented. Skew is a statistical measure that describes the symmetry of the frequency distribution and the value strongly affects flood frequency computations.
  • New computations for confidence intervals for the flood frequency curve are available to replace the simplified computation used in Bulletin 17B.

The Bulletin 17C guidelines have improved the computations for analyzing flood frequencies.  However, much work remains.  For example, while the guidelines recommend using an updated regional skew, the regional flood skew studies are still underway across much of the United States. Ongoing updates related to this work are available on the Subcommittee on Hydrology’s Bulletin 17C web page ( under “Flood Frequency Resources”).  In addition, methods need to be developed for addressing the regulatory effects of dams and the impacts of urbanization, and for incorporating estimates derived from application of deterministic models. 

Perhaps one of the areas in most need of development is how to address the assumption of climate stationarity that is still used in Bulletin 17C. As described in the new guidelines, there is much concern about changes in flood risk associated with interannual climate variability and long-term climate change.  The new guidelines recommend incorporating the impact of climate variability or change in flood risk when sufficient scientific evidence is available to quantify that risk. However, the new guidelines do not include evaluation of methods that might be used to do so.  Additional information and background on nonstationarity is presented in Olsen, Kiang, and Waskom (2010) and Kiang, Olsen, and Waskom (2011). 

To help analysts navigate climate change uncertainty, Bulletin 17C lists some useful references:

  • data on synoptic weather patterns (Hirschboeck, 1987);
  • paleoclimate information (Redmond, Enzel, House, and Biondi, 2002);
  • climate variability and climate projection information (Brekke and others, 2009);
  • interannual and interdecadal variations in climate (Jain and Lall, 2001); and,
  • time-varying distribution parameters (Stedinger and Griffis, 2011; Salas and Obeysekera, 2014).


Brekke, L.D., Kiang, J.E., Olsen, J.R., Pulwarty, R.S., Raff, D.A., Turnipseed, D.P., Webb, R.S., and White, K.D. (2009) Climate change and water resources management – A Federal perspective. U.S. Geological Survey Circular 1331.

England, J.F., Jr., Cohn, T.A., Faber, B.A., Stedinger, J.R., Thomas, W.O., Jr., Veilleux, A.G., Kiang, J.E., and Mason, R.R., Jr. (2018) Guidelines for determining flood flow frequency—Bulletin 17C. U.S. Geological Survey Techniques and Methods, book 4, chapter B5.

Hirschboeck, K.K. (1987) Hydroclimatically-defined mixed distributions in partial duration flood series.  In V.P. Singh (Ed.), Hydrologic Frequency Modeling (pp. 199–212). Baton Rouge: D. Reidel Publishing Company.

Jain, S., and Lall, U. (2001), Floods in a changing climate: Does the past represent the future?. Water Resources Research, 37(12) 3193–3205.

Kiang, J.E., Olsen, J.R., and Waskom, R.M. (2011) Introduction to the featured collection on “non- stationarity, hydrologic frequency analysis, and water management”. Journal of the American Water Resources Association, 47(3) 433–435.

Olsen, J.R., Kiang, Julie, and Waskom, Reagan (2010) Workshop on Nonstationarity, Hydrologic Frequency Analysis, and Water Management. Fort Collins, CO: Colorado Water Institute, Colorado State University.

Redmond, K.T., Enzel, Y., House, P.K., and Biondi, F. (2002) Climate variability and flood frequency at decadal to millennial time scales.  In House, P.K., Webb, R.H., Baker, V.R., and Levish, D.R. (Eds.), Ancient floods, modern hazards (pp. 21-45), American Geophysical Union Water Science and Application Series, v.5.

Stedinger, J.R., and Griffis, V.W. (2011) Getting from here to where? Flood frequency analy-
sis and climate. Journal of the American Water Resources Association, 47(3) 506–513.

Salas, J., and Obeysekera, J. (2014) Revisiting the concepts of return period and risk for nonsta- tionary hydrologic extreme events. Journal of Hydrologic Engineering, 19(3) 554–568.



International Stormwater BMP Database 

Jonathan Jones, P.E., P.H., D.WRE and Jane Clary

Wright Water Engineers, Inc. Denver, CO.

Eric Strecker, P.E., B.C.E.E. and Marc Leisenring, P.E.

Geosyntec Consultants, Inc. Portland, OR

Harry Zhang, Ph.D., P.E.

The Water Research Foundation, Alexandria, VA

The International Stormwater Best Management Practices (BMP) Database is a long-term collaborative effort focused on providing science-based information to advance the state of the practice for stormwater management.  The long-term purpose is to provide scientifically sound information that informs improved design, selection, implementation, cost-effectiveness and ultimately performance of BMPs. The Database includes voluntarily shared performance monitoring data and study site metadata in a consolidated, publicly accessible repository that can be used to support selection of BMPs appropriate to achieve stormwater management goals. Additionally, information in the Database can be used to set realistic expectations for BMP performance for various pollutants and to identify information gaps and research needs.

In the early 1990s, the American Society of Civil Engineers’ (ASCE) Urban Water Resources Research Council (UWRRC) recognized the lack of standardized technical design and performance data for urban stormwater BMPs that made the selection and design of BMPs based upon scientifically supported data difficult at best. To address this problem, the International Stormwater BMP Database Project ( was initiated.  Initially funded by the United States Environmental Protection Agency (USEPA) to meet the goals of the Clean Water Act (CWA), the Database has significantly expanded in scale from domestic to international studies.  Additionally, the Database includes studies of traditional urban stormwater controls as well as novel green infrastructure practices. These BMP types include grass strips, bioretention, bioswales, composite/treatment train BMPs, extended detention basins, media filters (mostly sand filters), porous pavement, retention ponds (wet ponds), green roofs, wetland basins, and wetland channels. It also includes distributed controls studies (Low Impact Development).  Over the past five years, the Project has also expanded to include not only urban stormwater BMPs but also agricultural and stream restoration BMP to support a variety of stormwater quality issues at the watershed scale.

Current efforts underway include development of a national cost database for stormwater BMP capital, and operation and maintenance costs.  Additionally, the National Cooperative Highway Research Program is supporting an effort to develop a more focused transportation portal to support the needs of state departments of transportation. In recent years, there have also been coordinated special projects with entities such as the Harris County Flood Control District in Texas and the National Fish and Wildlife Foundation working in the Chesapeake Bay. 

The Database cosponsors have also expanded over the years to include:

  • The Water Research Foundation, formerly as Water Environment & Reuse Foundation and Water Environment Research Foundation (manages the overall project)
  • Federal Highway Administration
  • Environmental and Water Resources Institute of ASCE
  • American Public Works Association
  • National Corn Growers Association
  • United Soybean Board
  • Urban Drainage and Flood Control District
  • National Cooperative Highway Research Program

Four “modules” are accessible through the Database website that can support communities working to attain Clean Water Act Goals. Figure 1 illustrates these four modules that include: Urban Stormwater BMPs, Urban Stormwater Runoff Characterization (NSQD), Agricultural BMPs, and Stream Restoration BMPs.   A Department of Transportation (DOT) BMP portal to the Urban Stormwater BMP Database is expected to be completed in late 2019.

The Urban Stormwater BMPs module, the original core of the database project, remains the largest repository of urban stormwater BMP design and performance study dataset in the world. The Urban Stormwater Database now hosts over 700 BMP studies, along with data analysis summaries of individual BMPs and overall BMP categories.  Studies include conventional BMPs, over 100 manufactured devices, and innovative green infrastructure practices, including over 60 bioretention sites.  The Agricultural BMP Database has focused primarily on practices to reduced nutrient and sediment loading in row crop settings, such as corn and soybeans. The Stream Restoration Databases is the newest of the databases and provides a framework for storing performance information for stream restoration projects.  The Stream Restoration Database serves as a companion project for WRF-sponsored guidance developed to support quantification of stream restoration benefits in the context of water quality crediting programs. The National Stormwater Quality Database (NSQD), developed by Professor Emeritus Robert Pitt of the University of Alabama, recently transitioned his work to the BMP Database website.  The NSQD contains urban runoff water quality characterization by land use for hundreds of field studies across the United States.

The overall repository of information on the Database website is useful in practice as it provides consolidated access to a variety of guidance and interpretive reports related to BMP design and performance at no cost.  For example, stormwater practitioners can find detailed monitoring guidance on performing and reporting on BMP studies, recommendations for statistically sound approaches for performance analysis, and reporting protocols, including data entry spreadsheets and user’s guides. The website also features on-line statistical analysis tools, presentations, and summary reports that focus on BMP performance for commonly monitored pollutants including suspended solids, nutrients, metals, and bacteria, as well as other pollutants when available (e.g., PAHs, PCBs, etc.).  The performance summaries are intended to provide technically and statistically sound analysis, presented in a straightforward manner that is usable by a wide range of entities such as municipal stormwater managers, regulatory agencies, university researchers, students and other stormwater professionals.  

To learn more about the International Stormwater BMP Database or to submit data, visit  



Equations for NRCS Unit Hydrograph

Michael A. Collins, PH, PE

Registered Professional Engineer, Texas, and District Engineer, West Brazoria County Drainage District No. 11, Brazoria County, Texas. Contact: [email protected]


The widely used standarized Natural Resources Conservation Service unit hydrograph is described by a tabular list of normalized discharges and runoff for various normalized times of runoff. To more easy apply this standarized hydrograph, particularly in analyses having only limited time and budget resouces, closely approximating equations using (i) the standard statistical “NORM” function readily available in MS Excel and (ii) empirically determined coefficents for mean and standard deviation are presented. The results suggests possible wider application of the technique presented in this paper.


The Natural Resources Conservation Service (NRCS, formerly the US Soil Conservation Service) standarized unit hydrograph (Mockus, 1969; US Soil Conservation Service, 1972) is often used for conducting hydrologic analysis of runoff. As noted by Pilgrim and Cordery (1992), the NRCS unit hydrograph is one of several enduring unit hydrographs used for hydrologic analysis and design (Clark, 1945; Debo and Reese, 2002; Hydrologic Engineeerng Center, 1982; Scharffenberg, 2016; Synder, 1938; see also the extensive online bibliographic listing of hydrograph-related reports from US government science agencies available at

This standardized NRCS unit hydrograph is described by a tabular list of normalized discharges and runoff volumes during the course of a storm event, as derived from a large number of natural unit hydrographs from many geographic locations and hydrologic regions (Texas Dept. of Transportationx, 2016).

Table 1 shows this time dependent hydrograph (both discharge and cumulative volume) and the tabular values upon which it is based. Many sources present these tabular values (e.g., Debo and Reese, 2002; McCuen, 1998; National Weather Service, 2005; US Soil Conservation Service, 1972; as well as the original work by Mockus, 1969, from which the values of Table 1 are drawn).

This NRCS hydrograph is incorporated in some computer programs, e.g., the Hydrologic Engineering Center-Hydrologic Modeling System (Scharffenberg, 2016; USACE, 1990), but use of comprehensive computer models may sometimes be eschewed by the hydrologist because of limited time and budget resources. Direct calculation of approximate hydrologic behavior, particularly in small scale drainage design projects, often relies upon methods using standardized, easily applied equations or formulas. However, such simplicity is in part lost for the NRCS unit hydrograph because it is described only by tabular values.

This paper presents closely approximating equations by which to describe the NRCS hydrograph for both discharge and volume. The application of these equations becomes quite simplified because the functions used are available via a standard spreadsheet formula in MS Excel.

Method: Approximating Equations

The formulas for closely approximating the NRCS unit hydrograph are based upon the normal probability density function, f(q), given by (using notation familiar to the hydrologist)

                        f(Q = q/qp ) = {1/[ S (2p)0.5} {exp {-0.5 [(T – T m)/S]2]}                                             [1]


in which exp(z) = ez; Q = q/qp is the dimensionless discharge, q is actual discharge, and qp is the peak discharge; T = t/tp is the dimensionless time (a random variable), t is actual time, tp is time of peak discharge, and Tm is the mean time of T; and S is the standard deviation of Q.

Fortunately, the normal distribution function f(Q) is a standard statistical function found in MS Excel, i.e., for dimensionless time T,

                                                  f(Q) = NORM(T, Tm, S, false)                                                         [2]


in which the logical variable “false” is used to indicate a probability density distribution. The NORM function is specialized for the purposes here as          

                                               Q = (KQ)NORM(T, T, SQ, false)                                                       [3]

in which SQ is the value of S for discharge and Kis introduced as a scale factor.

Likewise, the dimensionless hydrograph volume V as a function of Q is                                          

                                             F(V) =                                                                             [4]

in which F (V) = cumulative probability function, V = v/vis the dimensionless discharge volume, v = discharge volume, and vt is the total discharge and V is given in Excel by

                                                 V = (KV)NORM(T, Tm, SV, true)                                                        [5]

in which the logical variable “true”is used to indicate the cumulative probability distribution, Sv the standard deviation for the dimensionless volume curve, and Kis a scale factor.  

In both equations [3] and [5], Tm is set equal to 1 to position the dimensionless peak discharge at the dimensionless time Tm = 1.  KQ, KV, SQ , and Sare selected by trial and error to closely match the normal curve approximations to the NRCS curves.

To apply the NORM function to describe the NRCS unit hydrograph, the hydrograph is decomposed into four segments, as follows:

  • Pre-storm conditions: T<=  0,  Q = 0, and V=0
  • Pre-Peak Conditions: 0 < T ≤ Tm = 1
  • Post-Peak Conditions:  Tm = 1 <  T  ≤ Tr
  • Recession Condition:   T> Tr

In each segment, equations [3] and [5] apply, with the various parameters as given in Table 2. The coefficients K, Tr, SQ, and S depend upon the zone of the segmented hydrograph as given in Table 2. Note that Tr for the discharge curve is close to the inflection point for a normal distribution curve.

Accuracy of Approximation

The coefficients of Table 2 were selected by trial and error and tested with the degree of correlation they produced between the NRCS curves and the normal distribution approximations.

Figure 1 shows a plot of the NRCS discharge values vs. the normal distribution discharge values at similar dimensionless times. Figure 2 shows the comparison for the hydrograph volume values. While not a perfect match, a high correlation between the approximating equations and the NRCS values exists (R2>0.99).


Approximating equations using the normal probability function available in an MS Excel spreadsheet can be used to easily describe the tabular-described NRCS unit discharge model with sufficient accuracy for many practical applications. That an MS Excel function can be used for such description may in many applications facilitate wider application of the NRCS standard hydrograph. 

In addition, rainfall hyetographs (Huff, 1990a; Huff, 1990b; Kent, 1973; Merkel, Moody, and Quan, 2011; Natural Resources Conservation Service, 1986; NRCS, 2015; Texas Dept. of Transportation, 2016) are approximately similar in temporal behavior to the NRCS unit hydrograph. It is expected (but not yet demonstrated) that the method of this paper could sometimes be applied to such hyetographs as well as other standard hydrographs.

More generally, it is intriguing to suggest, and perhaps be explored by others, that runoff and the consequent hydrograph might be described as the net result of random generation of individual packets of runoff from various and individual parts of a watershed.


Clark, C.O. (1945), Storage and the Unit Hydrograph, Trans. Am. Soc. Civil Engrs., vol. 110, pp. 1419-1488.

Debo, Thomas N and Andrew J. Reese (2002), Municipal Stormwater ManagementSecond Edition, Lewis Publishers, pp 270-275.

Huff, F. A. (1990a), Time Distribution of Rainfall in Heavy Storms. Water Resources Research, 3, 1007-1019.

Huff, Floyd A. (1990b), Time Distributions of Heavy Rainstorms in Illinois, Circular 173, Illinois State Water Survey, State of Illinois, Dept. of Energy and Natural Resources.

Kent, K.N. (1973), A Method of Estimated Volume and Ratio of Runoff in Small Watersheds, Revised, US Soil Conservation Service, TP-149.

McCuen, R. H. (1998), Hydrologic Analysis and Design, 2nd Edition, Prentice-Hall, Inc. Englewood Cliffs, New Jersey, pp 534-543.

Merkel, William, Moody, Helen F., and Quan, Quan D.(2011), Rainfall Distributions for Ohio Valley and Neighboring States based on NOAA Atlas 14 Data, NRCS, Beltsville, Maryland (available at: htttps://

Mockus, Victor (1969), US Soil Conservation Service, National Engineering Handbook, Section 4, Hydrology, Chapter 16, Hydrographs (revised), pp 16.3 & 16.4).

Natural Resources Conservation Service (1986), Chapter 5 and Appendix A, Urban Hydrology for Small Watersheds (revised), TR-55, US Dept. of Agriculture.

NRCS (2015), United States Dept. of Agriculture, Hydrology National Engineering Handbook, Part 630, Chapter 4: Storm Rainfall Depth and Distribution, Part 630 (draft), pp 40-45.

National Weather Service (2005), Office of Hydrology, Hydrologic Research Laboratory, & National Operational Hydrologic Remote Sensing Center, Unit Hydrograph (UHG) Technical Manual.

Pilgrim, D. H., and I. Cordery (1992), Flood Runoff, Chap. 9, in D. R. Maidment, Editor in Chief, Handbook of Hydrology, McGraw-Hill, Inc., pp 9.30-9.31, 1992.

Scharffenberg, W. (2016), Hydrologic Modeling System HEC-HMS User’s Manual, UN Army Corps of Engineers, Institute for Water Resources, Davis, Cal., Rept. CPD-74A, pp 207-219.

Synder, W. M. (1938), Synthetic Unit-Graphs, Trans. Am. Geophys. Union, vol 19, pp 447-454.

Texas Department of Transportation (2016), Hydraulic Design Manual, Chap. 4-Hydrology.

US Army Corps of Engineers (1982), Hydrologic Analysis of Ungauged Watersheds Using HEC-1, Training Document No. 15, Hydrologic Engineering Center (HEC), Davis, Cal.

USACE (1990), HEC-1 Flood Hydrograph Package, Program Users Manual, Hydrologic Engineering Center (HEC), Davis, Cal.

US Soil Conservation Service

(1972), National Engineering Handbook, Section 4, US Dept. of Agriculture, Washington, D.C..





Treasurer’s Statement of AIH’s Financial Condition

Fiscal Year 2018 was a successful year for the American Institute of Hydrology. With detailed financial reports being made available through Adept, our management company hired mid-2017, and oversight provided by the Executive Committee, we are providing a report on the Institute’s financial condition. Going forward, we plan to make this an annual feature in our spring Newsletter to inform our membership.

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AIH Treasurer



Obituary: Robert Lee Vincent 

Former AIH member and leader Robert “Bob” Lee Vincent, 87, died on March 20, 2019, in Wichita, Kansas, following a short illness. He is survived by his wife, JoAnne, daughter Linda L. Vincent-Smith (Bradford Smith), son Brad C. (Alexis), and son Eric N. (Lisa). He also leaves six grandchildren, one great-granddaughter, and two brothers.

After high school, Bob worked for the Kansas Department of Transportation (KDOT) while also attending Kansas State University; he graduated in 1955 with a Bachelor of Science in Geology. Following graduation, Bob worked on the design of the first completed section of the Eisenhower Interstate System (1-70). In 1956, he completed his active duty obligation in the U.S. Army at Fort Bliss, El Paso, TX and was honorably discharged as a 2nd Lieutenant in 1957. He served as an officer in the U.S. Army Reserve 89th Division from 1957 through 1968, attaining the rank of Captain.

 Following active duty, Mr. Vincent returned briefly to KDOT before starting a career with Layne-Western Company, Inc. in Wichita, KS. In July of 1985, he founded Ground Water Associates, Inc., serving as president and chief hydrogeologist. He also served on the Advisory Committee to the Geology Department of Kansas State University as well as the Kansas Department of Heath and Environment. Bob was a certified professional geologist and hydrogeologist, as well as a registered professional geologist in Kansas, Arkansas, and Nebraska.  He served in leadership positions at the American Institute of Hydrology, the American Institute of Professional Geologists, the Association of Engineering Geologists, the Kansas Geological Society, and the American Water Works Association.  His work includes more than 60 years in ground water development, including aquifer location, well design, construction, and operation throughout the west and Midwest United States.

Additionally, he was a deacon of Metropolitan Baptist Church, a member of Rotary Club International, a board member for the Boy Scouts of American Quivira Council, and an active member of the Girl Scouts Golden Plains Council.


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