Summary of Recent AIH Board of Directors Annual Meeting

AIH’s Board of Directors (BOD) recently held its Annual Meeting virtually on December 2 and 3, 2022. The BOD reflected on accomplishments from 2022, and established goals, strategies, and tactics for 2023. Keep an eye out for some exciting items in the coming year with plenty of opportunities for active member engagement in various activities!

Institute Development Recap

The American Institute of Hydrology (AIH) played an important role at the American Water Resources Association (AWRA) Annual Conference that took place in Seattle, Washington, November 7-9, 2022. Salam Murtada (Director, Institute Development) and Dr. Zhong Zhang (Director, Academic Affairs) attended the conference and represented AIH.

On the first day of the conference, AIH facilitated a climate change contest during a 30-minute engagement break. The game involved grouping participants for brainstorming ideas on select climate change-related topics. An appointed spokesperson from each group then presented their team’s ideas. The level of engagement and dedication was remarkable; they were all winners!

During a technical session, Salam provided a presentation titled Certifying the Practice of Hydrology. Salam’s presentation was an overview of AIH – its mission, purpose, structure, membership, and process for certification of hydrologists.

Salam also participated as one of the panelists for the Student and Early Career Professional Development Luncheon to advise students and professionals about their careers in hydrology and benefits of certification for hydrologists.  

To promote our AIH membership and certification, AIH partnered with AWRA to offer 2022 Annual Conference attendees 50% off the membership application and examination fees. The collaboration also involved other benefits, such as featuring AIH information and items in conference materials, and e-mail blasts about AIH to all conference attendees.

As Gold Level Sponsors of the conference, AIH was able to present the 2022 AIH Awards during the conference Awards Luncheon. The Charles V. Theis Award for Groundwater, Ray K. Linsley Award of Surface Water, and Robert G. Wetzel Award for Water Quality were issued to Dr. Todd Halihan, Dr. Bruce Wilson and Dr. Vijay P. Singh, respectively, for their outstanding contributions to the field of hydrology. Dr. Halihan and Dr. Wilson accepted their awards in-person.  Dr. Singh accepted the award in absentia due to his residency overseas. The awardees offered important remarks during their acceptance speeches.

Dr. Todd Halihan, recipient of the Charles V. Theis Award for Groundwater, is a professor and Sun Company Clyde Wheeler Chair in Hydrogeology at Oklahoma State University, as well as Chief Technical Officer for Aestas, LLC. Dr. Halihan’s professional interests center in subsurface characterization using electrical hydrogeology and water supply sustainability.  He has been an associate editor for Groundwater and has served as the Secretary-Treasurer of the U.S. Chapter of the International Association of Hydrogeologists.  He served as the Chair of the Hydrogeology Division and the South-Central Section of the Geological Society of America. He was also the National Ground Water Association’s 2018 McEllhiney Lecturer. 

“This award,” remarked Dr. Halihan, “is named after C.V. Theis who had some serious negative feedback by establishing quantitative analysis for transient well hydraulics. In my work, I have tried to advance an approach similar to the energy industry of scanning, then drilling our groundwater sites to have a more comprehensive conceptual model. The negative feedback was surprising, but I found inspiration in the way Theis managed his detractors. The lesson I learned is to find guidance from supporters who want to see the science advance and change, which inspires me far more than those detractors that seem to like the status quo.”

Dr. Bruce Wilson,  recipient of the Ray K. Linsley Award for Surface Water, is a professor in the Department of Bioproducts and Biosystems Engineering at the University of Minnesota. Dr. Wilson’s research is focused on improving our understanding of hydrologic and water quality processes and erosion mechanics. Dr. Wilson has received awards from the American Society of Agricultural and Biological Engineering, Center for Transportation Studies, and the Erosion Control Association. Professor Wilson is also a recipient of the Distinguished Graduate and the Distinguished Undergraduate Teaching Awards, and the Charles E. Bowers Teaching Award.  He is a Fellow of the American Society of Agricultural and Biological Engineers.

“Our survival,” remarked Dr. Wilson, “the survival of human civilization – is dependent on the wise use of our water resources.  We should be proud – pat ourselves on our back – that our work is critically important.  But we should also be sober because our system is so complex – complex physical, chemical, biological components, and complex interactions among them.” Dr. Wilson acknowledged his colleagues, Dr. John Nieber (AIH Past-President) and Dr. Curt Larson, his graduate school advisor who happened to be Professor Ray Linsley’s PhD student.

Dr. Vijay P. Singh (AIH Past President), recipient of the Robert G. Wetzel Award for Water Quality, is a University Distinguished Professor, a Regents Professor, and Caroline and William N. Lehrer Distinguished Chair in Water Engineering at Texas A&M University. Dr. Singh has published extensively in the areas of hydrology, groundwater, water quality, irrigation engineering, hydraulics, and water resources (more than 1470 journal articles; 35 textbooks; 85 edited reference books; 121 book chapters; and 330 conference papers). He has received more than 107 national and international awards, and three honorary doctorates. He has served as President of AIH, Chair of Watershed Council of American Society of Civil Engineers (ASCE), and President of American Academy of Water Resources Engineers (AAWRE). He has served as editor-in-chief of three journals and two book series and serves on editorial boards of more than 25 journals and three book series. Dr. Singh is an Honorary diplomat of ASCE-AAWRE, a distinguished member of ASCE, a Distinguished Fellow of AGGS, a Distinguished Honorary Member of IWRA, and an Honorary Member of AWRA.

“I am deeply humbled to receive the award for two reasons,” remarked Dr. Singh. “First, Dr. Wetzel was a giant in the water quality field, and it is a rare honor for me to have my name associated with Dr. Wetzel. Second, I have long been associated with the American Institute of Hydrology, almost since its beginning years.  AIH is like my home institute inception and to be recognized by it is very special to me.” Dr. Singh acknowledged the support of his family, especially his late wife Anita, students and colleagues, among others.

The award ceremony concluded after honoring outstanding hydrologists and giving tribute to the leaders of the past, who paved the way for them to continue their important work.

Thanks to its leaders and organizers, AWRA delivered a very successful Annual Conference in 2022!

Former AIH Presidents Deliver Keynote Addresses at IWA Conference in Istanbul, Türkiye

Dr. Miguel A. Medina, Jr., PH, F.ASCE (Professor Emeritus, Duke University)

Dr. Mustafa Aral, PH, F.ASCE (Professor Emeritus, Georgia Tech University)

The Republic of Türkiye changed its official name from The Republic of Turkey on 26 May 2022, in a request submitted to the United Nations Secretary-General by the country’s Minister of Foreign Affairs. It was indeed unique that two former American Institute of Hydrology presidents, Dr. Miguel Medina Jr (2009-2010) and Dr. Mustafa Aral (2015-2016) presented keynote addresses in a country far away from the USA! The events unfolded at the International Water Association (IWA) 4thRegional Conference on Diffuse Pollution and Eutrophication (IWA DIPCON 2022) in Istanbul, Türkiye, held at the Istanbul University main campus, from October 24-28, 2022.

Drs. Aral and Medina enjoying a traditional Turkish meal.
The Bosphorus Straight.

Lunches for conference speakers, organizers and participants were held at the historic and ornate Istanbul University faculty dining room.

A conference welcoming cruise along the Bosphorus proved to be one of the highlights of the conference social activities. The Bosphorus Strait is an internationally significant waterway. It forms part of the continental boundary between Asia and Europe. However, there are now three bridges and a tunnel connecting the European side of Istanbul to the Asian side. A brand-new cruise ship terminal (Galataport) is illustrated below. The Bosphorus allows shipping from the Black Sea to the Sea of Marmara and vice versa. A field trip to dams and aqueducts providing water to European Istanbul was organized on the last day of the conference, October 28th.

A view of Galataport from the cruise ship.

It Takes a Village: Managing Water in a Time of Climate Change

Rouzbeh Berton, PE (Hydrologist, Stantec)

Carmen Bernedo-Sanchez, PE (Hydrologist, Stantec)

Rouzbeh Berton, PE
(Hydrologist, Stantec)
Carmen Bernedo-Sanchez, PE (Hydrologist, Stantec)

Though dams have existed for centuries, many large dams were built throughout the United States as early as 100 years ago. Initially, dams mainly stored excess water for later use—typically during a drier part of the year. However, dams have grown to become multipurpose infrastructures supporting hydropower generation, drinking water demands, and industrial water supply. Now, we are highly dependent on our dams and the water they store.

Scientists caution that climate change, and the increasing number of extreme weather events, will significantly impact our water resources. In recent years, weather patterns have changed so much, that the rainfall is not as predicable (e.g., Salas et al., 2020; Xu et al., 2022). Many places are getting most of their annual rainfall in a few intense events, while the rest of the year is dry (e.g., Ingram, 2016). Instead of slowly gaining and releasing water throughout the year, in some areas, reservoirs are seeing an influx of a year’s worth of rainfall all at once (e.g., Fleming & Weber, 2012; Maddu et al., 2022; Naz et al., 2018; Yu et al., 2014). This change might not seem significant, but existing dams were simply not designed to accommodate storm water like that.

Imagine a dam is almost full, and a major rainstorm happens. If the dam fills more, it could overflow, and dam safety would be a concern. Likely, you would open the dam gates to release some of the extra water. This prevents water from spilling over the top and prevents the dam from failing entirely. But, if you open the gates, you are losing water. Then, what happens during the dry months?

There are many stakeholders who can contribute to a sustainable watershed. Let us take a closer look at some potential solutions for managing water in a time when precipitation patterns are changing. We can design for excess water, store as much water as possible, and be responsible water stewards.

Designing for Excess Water

This is where urban planners step up—by planning how the city fits into the watershed and how water moves in and around the city. The closer buildings, parking lots, and asphalt roads are to the reservoir inlet, the more quickly large amounts of runoff will enter the reservoir. When impervious surfaces—like concrete and asphalt—are evenly distributed across a watershed, instead of being concentrated in specific locations, it slows down the movement of water (e.g., Ariano & Oswald, 2022; de la Cretaz & Barten, 2007; Roodsari & Chandler, 2017). This concept allows for sustainable development while mitigating the excess flow and delaying the amount of water entering the reservoir (e.g., Liu et al., 2022; R et al., 2020; Wang et al., 2021).

In addition to planning where major developments are built in relation to the reservoir, green spaces within a city are also important. In a dense cityscape, think of green spaces like small sponges. The vegetation can soak up some of the water where it slowly drains into the groundwater system, instead of running off as stormwater and entering a reservoir.

Some urban areas even plan for water collection in and on areas that typically would have just been a source of runoff water. For example, landscape architects can incorporate water-absorbing green roofs where appropriate. Some locations that are prone to flooding might want to consider porous asphalt, where water slowly seeps through roads and parking lots instead of running off or pooling up.

Lastly, from a planning perspective, accounting for how the city will grow can lessen flood consequences. Planners can limit urban expansion to areas outside of potential flooding areas. Landscape architects working together with engineering designers can create resilient watersheds. This will help minimize the impact of climate change to our reservoirs.

Maximizing Water Storage

Sometimes, dam owners can raise the height of the dam to accommodate for more intense rainfall. Though, this solution is not always a viable option. As such, we should think about managing the water before it enters the reservoir. Upstream management measures can be innovative and cost-effective. For instance, several detention ponds can be built to temporarily store the incoming water and gradually release it to reduce the pressure on the main reservoir during an extreme event. Appropriate measures can vary from one watershed to another, but ponds might be a simple and cost-effective solution.

While detention ponds offer a good potential solution, there are also two key drawbacks that make them a less-attractive option. First, dam owners often do not own the upstream lands in the watershed, so trying to build a dam and manage water on someone else’s land might not be possible. Second, from a risk perspective, adding upstream detention ponds increase the risk downstream. If a smaller upstream dam failed, it would release that water all at once, adding greater strain on the main reservoir dam.

If building a pond or additional reservoir is not feasible, there could be a middle-ground approach of reclaiming or expanding wetlands. A wetland area can provide a natural buffer to soak up excess water upstream of a reservoir. Wetlands also bypass the two major concerns of the temporary detention ponds. Wetlands may be easier to get permission to create or expand, and there is less risk since there are no additional dams to monitor.

Responsible Water Stewardship and Applying Ancestral Lessons

With weather forecasting, we can all be aware of rain patterns, and can even be notified not to water our lawns and outdoor plants before an extreme rainfall event. Some sprinkler systems run from a timer and will go at the same time every day even if it is raining! Rainwater that is absorbed into your yard recharges our groundwater system instead of flowing directly into a reservoir.

Some of the most sustainable and effective measures are not necessarily the most high-tech. Humans have been managing water for centuries, adopting effective means of storing water to survive droughts, even in arid climates. Community members can contribute to effective water management by understanding and applying lessons learned from our ancestral past. Do not discount your role in managing our limited water resources; we all play a part!


Ariano, S. S., & Oswald, C. J. (2022). Broad scale assessment of key drivers of streamflow generation in urban and urbanizing rivers. Hydrological Processes, 36(4), e14579.

de la Cretaz, A. L., & Barten, P. K. (2007). Land Use Effects on Streamflow and Water Quality in the Northeastern United States (0 ed.). CRC Press.

Fleming, S. W., & Weber, F. A. (2012). Detection of long-term change in hydroelectric reservoir inflows: Bridging theory and practise. Journal of Hydrology, 470–471, 36–54.

Ingram, W. (2016). Extreme precipitation: Increases all round. Nature Clim. Change, 6(5), 443–444.

Liu, W., Qian, Y., Yao, L., Feng, Q., Engel, B. A., Chen, W., & Yu, T. (2022). Identifying city-scale potential and priority areas for retrofitting green roofs and assessing their runoff reduction effectiveness in urban functional zones. Journal of Cleaner Production, 332, 130064.

Maddu, R., Pradhan, I., Ahmadisharaf, E., Singh, S. K., & Shaik, R. (2022). Short-range reservoir inflow forecasting using hydrological and large-scale atmospheric circulation information. Journal of Hydrology, 612, 128153.

Naz, B. S., Kao, S.-C., Ashfaq, M., Gao, H., Rastogi, D., & Gangrade, S. (2018). Effects of climate change on streamflow extremes and implications for reservoir inflow in the United States. Journal of Hydrology, 556, 359–370.

R, M. K., L, H. S., Jia, L., Trevor, H., & Shawn, H. J. M. (2020). Spatial Configurations of Land Cover Influence Flood Regulation Ecosystem Services. Journal of Water Resources Planning and Management, 146(11), 04020082.

Roodsari, B. K., & Chandler, D. G. (2017). Distribution of surface imperviousness in small urban catchments predicts runoff peak flows and stream flashiness. Hydrological Processes, 31(17), 2990–3002.

Salas, J. D., Anderson, M. L., Papalexiou, S. M., & Frances, F. (2020). PMP and Climate Variability and Change: A Review. Journal of Hydrologic Engineering, 25(12), 3120002.

Wang, Y., Zhang, X., Xu, J., Liang, C., She, D., & Xiao, Y. (2021). Evaluating effects of urban imperviousness connectivity on runoff with consideration of receiving pervious area properties. Urban Water Journal, 18(8), 598–607.

Xu, Z., Chang, A., & di Vittorio, A. (2022). Evaluating and projecting of climate extremes using a variable-resolution global climate model (VR-CESM). Weather and Climate Extremes, 38, 100496.

Yu, P.-S., Yang, T.-C., Kuo, C.-M., Chou, J.-C., & Tseng, H.-W. (2014). Climate change impacts on reservoir inflows and subsequent hydroelectric power generation for cascaded hydropower plants. Hydrological Sciences Journal, 59(6), 1196–1212.

President’s Message – Fall 2022

AIHPresident Jamil IbrahimThis is an overdue update to our AIH members and community about what your AIH leadership team has been up to this year. I am thrilled to announce completion of critical and timely updates to the governing documents for our organization – our AIH Articles of Incorporation (formerly, Constitution) and AIH Bylaws. We initiated the review and update process in 2016. Over the past six years, past and current AIH leadership team members devoted many, many hours to completing a comprehensive review and developing suggested revisions to these documents. This review and update provided a great opportunity to reflect on how we have operated and how we will function in the future. In the spirit of these changes, Leonardo Da Vinci once remarked (translated to English): “When you put your hand in a flowing stream, you touch the last that has gone before and the first of what is still to come.” It is extremely gratifying to see the results of our review/update process in our new governing documents, and I look forward to the next steps.

There are many other great updates to share:

·        Diversity, Equity, and Inclusion (DEI) Committee – Our DEI Committee developed and prioritized a list of initiatives and solicited feedback/input on implementation through a virtual meeting held in March of 2022. Please reach out to Julé Rizzardo (President-Elect) to join the DEI Committee and learn about these great initiatives.

·        Annual Meeting – Our leadership team held our (delayed) Annual Meeting virtually during March 2022. The meeting was supposed to be held during December 2021, to set our trajectory for 2022, but was delayed due to COVD concerns. In addition to specific tactics associated with strategies and goals that were identified by the Executive Director and members of our Board of Directors, we established three “working groups” to address: (1) Technical Journal/Conference Collaboration; (2) promotions, swag, and marketing; and (3) coordination with affiliate organizations. Contact myself or our management office to learn more and get involved. We are scheduled to get back on track and hold our Annual Meeting in December of 2022 (hopefully, in-person) and set plans for 2023.

·        AIH Webinars – Continued our AIH webinars with great presentations by AIH members Richard Koehler (PhD, PH) and Andrew Cohen( PhD, PH).

·        Engagement with Affiliate Organizations – Continued our engagement with other organizations through promoting PH certification for hydrologists and HT certification for hydrologic technicians at the 2022 World Environmental & Water Resources Congress (EWRI); Frontiers in Hydrology Meeting co-sponsored by the American Geophysical Union (AGU) and CUAHSI (Consortium of Universities for the Advancement of Hydrologic Science, Inc.); and 11th International Symposium on Managed Aquifer Recharge (ISMAR).

·        AIH 2022 Awards – We Issued our distinguished AIH awards to our 2022 award winners: Bruce Wilson, PhD (Ray K. Linsley Award for Surface Water); Todd Halihan, PhD (Charles V. Theis Award for Groundwater); and Vijay P. Singh, PhD, PH (Robert G. Wetzel Award for Water Quality). Note, we will present these awards to our award winners this year at the American Water Resources Association (AWRA) 2022 Annual Conference during their Awards Luncheon on November 9, 2022, in Seattle, Washington.

·        Examination Questions Database Update – We have a plan in place and are about to embark on a comprehensive update to our database of examination questions for our AIH certification exams. Updates will be completed prior to our next round of examinations, scheduled for November 2022.

As I’ve stated in each of my messages previously, member participation is vital to AIH’s success. We are eager to engage more members in AIH activities. Please reach out to our Secretary/Membership Liaison, Jolyne Lea, at, to get involved.


Jamil S. Ibrahim PH, PMP, ENV SP
AIH President, 2021-2022

Spotlight on Recent AIH Exams and on New Members

Congratulations to those who recently passed their exams during May 2022!

Hydrologist-in-Training – Fundamentals (Part I)

Madeline Richards, HIT

Kaiylyn Chow, HIT

Robert Sheridan, HIT

Professional Hydrologist – Principles and Practices (Part II)

John Shuler, PH (Surface Water)

Benjamin Von-Thaden, PH (Surface Water)

Congratulations to New Members

Congratulations to those who have been recently certified as Professional members of the American Institute of Hydrology!

Max Strickler, PH (Surface Water)

Matt Sparacino,  PH (Surface Water)

John Shuler, PH (Surface Water)

Benjamin Von-Thaden, PH (Surface Water)

Recap of AIH Webinars

AIH was honored to feature two webinars by outstanding hydrologists and AIH members, Richard Koehler, PhD, PH, and Andrew Cohen, PhD, PH.

On June 16th, Dr. Richard Koehler presented a webinar titled, “A Novel Approach to Quantify Streamflow Properties”. During the webinar, Dr. Koehler presented a novel approach using autocorrelation lag (k) plots and sequence summations to quantify several stream flow properties, including magnitude, frequency, duration, timing, and rate of change. To learn more about the approach, please refer to his article featured in this Bulletin titled, “The Lag 1 Hydrograph – Alternate Way to Plot Streamflow Time-Series Data”.

In collaboration with the American Water Resources Association (AWRA), AIH presented a webinar on July 13th by Dr. Andrew Cohen titled, “Introduction to the GroundwaterU Video Public Library – a new and free educational resource”. During the webinar, Dr. Cohen introduced GroundwaterU as an educational platform that serves to make groundwater knowledge accessible globally by way of high-quality and engaging educational videos. For more information about GroundwaterU, please visit the following link: Home – GroundwaterU

Institute Development Recap

AIH continues to collaborate with other professional organizations in order to promote our common goals of enhancing and strengthening the standing of hydrology as a science and profession. Through other organizations, we have been reaching out to hydrologists, hydrologic technicians, and students currently pursuing formal education in a field related to hydrology.

On April 12 -14, 2022, AIH collaborated with Groundwater Resources Association’s (GRA’s) 11th International Symposium on Managed Aquifer Recharge (ISMAR11), held in Long Beach, California, by contributing financially to their World Access Sponsorship. This sponsorship helped provide free live-streaming access to attendees joining virtually from other countries who were not able to travel to the conference.

On June 6-8, 2022, AIH Board of Directors members, Yige Gao, PH (Director, International Affairs) and George McMahon, PhD, PH (Director, Policy and Advocacy) attended the American Society of Civil Engineers (ASCE) Environmental and Water Resources Institute (EWRI) Congress in Atlanta, GA, where they presented and initiated partnerships with other hydrology-related organizations. Yige also presented on ‘Certifying the Practice of Hydrology’ for a student session.

On June 19-24, 2022, AIH Board of Directors member, Zhong Zhang, PhD, PH (Director, Academic Affairs) attended the Frontiers in Hydrology Meeting (FIHM), Puerto Rico, which was co-sponsored by the American Geophysical Union (AGU) and Consortium of Universities for the Advancement of Hydrologic Science, Inc. (CUAHSI). AIH purchased a meter board to reach out to hydrologists and promote our membership. Zhong interacted with conference attendees interested in learning about AIH and its membership.

Photo: Dr. Zhong Zhang standing next to the AIH meter board, at the June CUAHSI-AGI Conference, Puerto Rico.

The Lag-1 Hydrograph – An Alternate Way to Plot Streamflow Time-Series Data


An alternate approach is presented where graphing discharge can be accomplished without a time axis. This technique allows data properties such as Q, dQ/dt, and d2Q/dt2, and trends of increasing, decreasing or no change flow to be readily seen and understood on a single graph. Flow pulse reference lines can easily be added and interpreted. The methodology is based on the time-series serial correlation lag-1 graph and uses the normally unwanted (but still valuable) autocorrelation present within the streamflow data. Examples and applications are included.

Key words: Lag-1 hydrograph, autocorrelation, 1st, 2nd order derivative, hydrograph analysis


Hydrographs are an essential tool for hydrologists or other water resources professionals. The USGS defines a hydrograph as “a graph showing stage, flow, velocity, or other property of water with respect to time.” (Langbein and Iseri, 1960). Note there is no rigid requirement that a time axis be used when plotting time-base data, though this is the most common method. Another approach is demonstrated in this paper.

Lag-1 Hydrograph Method

Data preparation and plotting are identical to an autocorrelation lag 1 plot, where 1 indicates a 1-day time shift. Table 1 shows how the time-series discharges are shifted. For this paper, the unshifted discharge is labeled Qt (the x coordinate) and the shifted discharge Qt+1 (the y coordinate). It is critical that the temporal sequence is maintained for the data. Thinking of the x values as “flow for today” and the y values as “flow for tomorrow” helps to visualize the order of the data.


Table 1. Data shift example (USGS site Colorado River at Lees Ferry, AZ)

To calculate discharge change, a ratio between the coordinates is used. This ratio can be used as a reference on the plot. For these equations below, the (x,y) coordinate is (Qt, Qt+1). In all cases there is a 1-day time step so that the change in time (Dt) is 1.

Equation 1a             y = mx  

Equation 1b             Qt+1 = m Qt

where m = change ratio

Equation 2              m = y/x = (Qt+1) / (Qt)                   

                               where m > 1, discharge is increasing

          m = 1, no change to discharge

                                         m < 1, discharge is decreasing

Equation 3a              y – x             = Qt+1 – Qt     = DQ/day    

Equation 3b              (m – 1) Qt   = Qt+1 – Qt = DQ/day


A traditional line hydrograph for the data in Table 1 is shown in Figure 1.

Figure 1. Line hydrograph for the Colorado River at Lees Ferry, AZ


The hydrograph represents runoff from a Pacific hurricane remnant that crossed into the southwestern United States (Weaver, 1968). The multiday event provides a useful example to display and discuss properties of the Lag-1 hydrograph.

A key item with this approach is that time is employed as a data attribute rather than as a coordinate. The lag-1 hydrograph (Figure 2) allows for additional information such as regions of increasing, decreasing or no change in discharge. An interesting feature of this plot is that the first and second order derivatives of the discharge are displayed.

Consider the following data representations on a Lag-1 hydrograph:

1.  The x coordinate of a data point represents the daily discharge (Qt)

2.  Each data point represents DQ/day or dQ/dt (1st order derivative)

3.  Lines connecting points represent D(DQ/day) or d2Q/dt2 (2nd order derivative)

The details listed above are comparable to distance (item 1), velocity (item 2), and acceleration (item 3) from the physics of motion. Regions are highlighted below.

Figure 2. Lag-1 hydrograph example (day number associated with Qt).



Figures 1 and 2 use the same data but display very different graphics.

Below are detailed comparisons of the two plots:

Days 11 to 12 – The line hydrograph shows little change between these two days, while the lag-1 hydrograph shows a single point very close to the y = 1x ratio change line.

Days 12 to 13 and 13 to 14 – The line hydrograph shows the rising limb of the event. The lag-1 hydrograph shows days 11, 12, 13, and 14 are all above the 1x line, indicating rising flow conditions. But because the distance of the points decreases from the 1x line, this shows the increases are occurring, but at a decreasing rate. Day 14 shows the peak for Qt+1, while Day 15 shows the peak for Qt. Both represent the discharge on 15 Sept 1927.

Days 15, 16, 17 and 18 – the line hydrograph shows decreasing flows. The lag-1 hydrograph also shows the decreasing flow conditions as all points are below the 1x line.

Additionally, the rate of change for the decrease is consistent. A power curve fitted to these points yields a recession equation for the general form aQb where Qt+1 = 1.8124 Qt 0.9198. This is consistent with the extraction method of baseflow recession segments based on a second-order derivative (Yang, et al., 2020).


Discussion & Conclusion

This paper is a brief overview of a new technique that does not appear elsewhere in the published literature. Here are three ways this technical approach can be used in water resources projects. First – use this method for model calibration by having the x axis be the observed data and the y axis be the modeled data. The resulting plot would be an “error hydrograph” showing time and discharge differences. Next – scale up the data used from one runoff event to a multi-year discharge record with the x axis as Qt and the y axis as Qt+1. The resulting plot becomes an autocorrelation lag 1 plot but now with the Q, dq/dt and d2Q/dt2 regions. Additionally, the autocorrelation r(k), a metric of persistence and randomness, can be calculated. Finally – let an upstream gaging station be the x axis and a downstream station, lagged by the routing time, be the y axis. The resulting plot will show the contribution of the local, ungaged area between the two stations.

A more in-depth treatment of this novel approach is available as a webinar (June 16, 2022) sponsored by the American Institute of Hydrology (AIH webinar, 2022).


The author thanks AIH for the opportunity to share this self-funded research.


AIH webinar. 2022. A Novel Approach to Quantify Streamflow Properties,

Langbein, W. B., and Iseri, Kathleen T., 1960. General Introduction and hydrologic definitions: U.S. Geol. Survey Water-Supply Paper 1541-A, 29 p.

Weaver, R. 1968. Meteorology of Major Storms in Western Colorado and Eastern Utah. Technical Memorandum WBTM HYDRO-7. U.S. Dept. of Commerce, Environmental Science Services Administration, Weather Bureau.

Yang, W., C. Xiao, and X. Liang. 2020. Extraction Method of Baseflow Recession Segments Based on Second-Order Derivative of Streamflow and Comparison with Four Conventional Methods. Water. 12. 10.3390/w12071953.

About the Author

Dr. Koehler is the CEO of Visual Data Analytics and a certified professional hydrologist with over 40-years’ experience.

Previously he was the National Hydrologic and Geospatial Sciences Training Coordinator for NOAA’s National Weather Service and is a retired NOAA Corps lieutenant commander. Assignments included navigation and operations officer for two NOAA oceanographic research ships, the Colorado Basin River Forecast Center and the Northwest River Forecast Center where he oversaw the implementation of an operational dynamic wave model for Lower Columbia River stage forecasts. Other positions include Director of Water Resources for an Arizona consulting company and the water resources hydrologist for Cochise County, Arizona. 

He is also a member of the science department faculty at Front Range Community College and is instructor for astronomy, geology, geography, GIS and geodesy courses. He is also an FAA certified professional drone operator.

He has a PhD, MS and BS in Watershed Management from the University of Arizona and an additional MS in Hydrographic Sciences from the US Naval Postgraduate School. The focus of his research are alternate methods of analyzing environmental time-series data along with associated data visualizations. 

Hydrologic Engineering Center Hydrologic Modeling Systems (HEC-HMS) version 4.10

By: HEC-HMS Team


The Hydrologic Modeling System (HMS) is software developed by the Hydrologic Engineering Center designed to simulate precipitation-runoff processes of dendritic watershed systems. HEC-HMS provides a wide range of scalable methods for modeling hydrologic processes, delivers a modern and efficient user interface, supports robust optimization and uncertainty analysis capabilities, and has available complete documentation and training options for the engineering community. It is designed to be applicable for a wide range of geographic areas to solve the widest possible range of problems. This includes large river basin water supply and flood hydrology, and small urban or natural watershed runoff. 

The HEC-HMS team has recently modernized its software development process following Continuous Integration & Continuous Delivery principals. The results have been faster releases of new features, quicker turnaround for bug fixes, lower bug count in the official release, and easier collaboration with other developers. The current development version of HEC-HMS is version 4.10, which is planned to be released by summer of 2022. HEC-HMS version 4.10 includes numerous updates to the software, including a new compute option, new and refined meteorological methods, enhanced methods to display spatial results, and many more improvements. Other improvements and features that will be released with 4.10 include: 

  • Dynamic Reservoir Volume Reduction Method
  • Simplex Optimization Improvements
  • Resume Differential Evolution Optimization
  • Normalized Nash-Sutcliffe Efficiency Optimization Objective Function
  • Peak-Weighted Variable Power Optimization Objective Function
  • Snowmelt Plots
  • 2D Diffusion Wave Transform and 2D Sediment Transport Enhancements

We encourage users to visit the HEC-HMS webpage to learn more about current software updates:

Frequency Analysis Compute

The new Frequency Analysis compute option in HEC-HMS is similar in nature to the existing Depth-Area Analysis framework that analyzes multiple points within a watershed at a single frequency. The Frequency Analysis compute option allows the user to analyze a single point over a range of different frequencies. A Frequency Analysis can have one to many ordinates defined, each with their own assigned annual exceedance probability, meteorological model, and basin model. Currently, the analysis can be used to generate a flow frequency curve or a stage frequency curve at the point of interest. Figure 1 shows the computed peak flow frequency curve output window from HEC_HMS at a specified location. 

Figure 1: Peak flow frequency curve generated from Frequency Analysis compute option

Interpolated Meteorology 

An interpolation option was added to the precipitation, temperature, windspeed, solar radiation, and evapotranspiration methods in the meteorological model. The interpolation option interpolates between gaged locations and creates a series of time-series grids over a gridded domain, or time-series at point locations if interpolating over a non-gridded domain. The interpolation can be performed over a range of time increments (daily, sub-daily, etc.) and simulation time-steps. The interpolation methods include inverse-distance squared, inverse-distance, nearest-neighbor, and bilinear. There is an option to bias correct a precipitation interpolation and lapse adjust a temperature interpolation. The interpolated results are cached to disk in an HEC-DSS file. The cached results are accessed on subsequent computes, unless a parameterization change occurs and invalidates the cache, triggering a re-compute. The time-series gages that are selected for interpolation must be parameterized with a valid longitude and latitude. Figure 2 shows the HEC-HMS Map Window demonstrating the interpolated precipitation capabilities for the Truckee River watershed.

Figure 2: Interpolated precipitation grid computed from point rainfall gages and PRISM bias grid using the Interpolated Precipitation meteorological method

Frequency Storm Meteorological Model Enhancements

New features for the Frequency Storm and Hypothetical Storm precipitation methods streamline their use for flow-frequency simulations. Multiple precipitation frequency grids downloaded from NOAA Atlas 14 can now be imported using the Precipitation Frequency Grid Importer. This feature also internalizes external source files for the grids by copying them to the project directory. The Frequency Precipitation Calculator tool can be used to quickly calculate average precipitation depths. These computed precipitation depths can be applied at either the watershed or subbasin level. Figure 3 shows the Frequency Precipitation Calculator. The Frequency Depths Calculator is only available if the meteorological model has been linked to a subbasin model that contains georeferenced subbasin elements. 

Figure 3: Frequency Precipitation Calculator using NOAA Atlas 14 Precipitation-Frequency grids

The frequency storm meteorological model also allows for a User-Specified area reduction method to be applied, shown in Figure 4. This new option allows the user to specify a depth area-reduction function and apply it to each of the inner durations of a frequency storm. 

Figure 4: User Specified Areal reduction factor for each precipitation duration

Viewing and Exporting Spatial Results

The HEC-HMS team is constantly developing new and improved options for visualizing model results. Evaluating model performance is critical for model refinement and conveying results. A legend, scale bar, and north arrow can now be displayed within the desktop when a valid spatial result or calibration metric is selected. These options can be enabled through the View menu. An example of these new visualization items is shown in Figure 5. Additionally, Min and Max buttons were added to the Spatial Results toolbar that allow for quick visualization of the minimum or maximum values of any spatial result regardless of the time in which they were computed. 

Figure 5: Legend, scale bar, and north arrow displayed for the Truckee River watershed Map window.  Min and Max buttons also shown on Spatial Results toolbar

An Export Snapshot button and an Export Recording button were added to the Spatial Results toolbar. The Export Snapshot button, when pressed, will allow the user to export the currently selected spatial result at the current display time step as a GeoTIFF file. The resultant file will be georeferenced and can be read by common GIS software (e.g., QGIS, ArcGIS). The Export Recording button, when pressed, will allow the user to export an animation of the currently selected spatial result to either AVI or MP4 file. The resultant animation will also include any currently displayed maps, such as subbasin outlines, reservoir icons, and terrain.

The Spatial Results toolbar can show calibration results for flow and snow water equivalent (SWE). This feature adds visuals for assessing the calibrated state of a basin model. Computed statistical metrics, such as Nash Sutcliffe Efficiency (NSE), Coefficient of Determination (R2), Root Mean Square Error / Standard Deviation (RSR), and Percent Bias (PBIAS), are used to color-code each subbasin, as shown in Figure 6. 

Figure 6: Spatial Results calibration results map layer for flow 


About Authors

The HEC-HMS Team consists of Matthew Fleming, Thomas Brauer, Michael Bartles, Gregory Karlovits, Jay Pak, Nick Van, Josh Willis, Daniel Black, Natasha Sokolovskaya, Alex Sanchez, Alex Davis, and David Ho. Team members all work for the U.S. Army Corps of Engineers and come from a wide variety of backgrounds – Civil Engineers, Hydrologists, Geologists, and Computer Scientists. All team members are competent in multiple disciplines of HMS teamwork, such as developing the software, testing the software, documenting, training, providing technical support, and supporting with hydrologic studies.

Any questions about this article can be directed to David Ho at



Gene Kim, Patrick Debois, John Willis, and Jez Humble. 2016. The DevOps Handbook: How to Create World-Class Agility, Reliability, and Security in Technology Organizations. IT Revolution Press.