Long-Range Water Supply Planning in the Town of Cary, North Carolina

Whitney Reynier Rachel M. Gregg
Posted on: 12/21/2017 - Updated on: 3/02/2020

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Project Summary

The Town of Cary, North Carolina, recently completed an update to its Long-Range Water Resources Plan. The plan update incorporates a probability-based look at how various factors influence water supply, such as population growth and climate variability. The plan update also identifies priority strategies and includes an implementation plan to ensure resilient and sustainable water management through 2060.


The Town of Cary provides water, stormwater, and wastewater services to approximately 152,000 residents located in the Triangle Region of North Carolina. Cary has been involved in long-term water resources planning since 2000, in order to maintain high-quality water supply service for the Town’s residents and businesses in the future, and to do so in a financially and environmentally responsible way. Although this region typically has an abundance of water, two droughts of record have occurred in the recent past, and the Town recognizes that variability in factors such as customer demand, land use, and climate (including drought, temperature increases, and extreme weather events) could affect water supply if not planned for accordingly. In addition, expected population growth in the region underscores the importance of water supply planning for the future.

The Town of Cary developed and published its Long Range Water Resources Plan in 2013. The Plan builds off of previous plans published in 2000 and 2007, and addresses the continuation of the Town’s water conservation and reclaimed water use programs. The Plan complements other Town efforts to enhance stormwater management, protect open space, and utilize green infrastructure to improve and maintain flood and water quality protection.

Funding for the Long Range Water Resources Plan came from each of the areas for which the plan was developed, including the Town of Cary and the Town of Morrisville, the Town of Apex, and Wake County/Research Triangle Park. The Town of Cary, which provides water services to the Town of Morrisville, funded plan development using utility capital revenue sources. Total expenditures for plan development were $584,300 for the Town of Cary and $116,850 for the Town of Apex. Expenditures incurred by Research Triangle Park were not available at time of publication.


Building off of previous water planning efforts, the 2013 Long Range Water Resources Plan (LRWRP) followed a very comprehensive process and integrated a variety of information to ensure resilient and sustainable water management for the Town of Cary. Initially, the planning team conducted surveys of other national water resource managers with advanced water resources programs and/or sustainable and diverse water resources portfolios. Information gathered from interviews was used to validate and inspire strategies and resources developed during the planning process. One interesting finding from these surveys was that, at the time, few utilities had accounted for climate variability, although integration of this type of information in water supply planning is increasing.

The planning team then conducted a series of four workshops with municipal and county staff and a consulting senior advisory panel. The purpose of these workshops was to 1) facilitate conversations about critical components to consider during the plan update, 2) develop a decision framework to guide decision-making during the planning process, 3) clarify the overall goal of the plan update, identify core values, and outline criteria and objectives critical for achieving plan success, and 4) to screen a list of potential water resource strategies gathered from previous workshops, interviews, local expert knowledge and experience, and additional research to identify those strategies most likely to fit the needs of the LRWRP. This final stage resulted in a shortlist of 22 strategies that the planning team carried forward through the planning process.

The Plan integrated a variety of new information. A series of directed technical evaluations were completed, including a review of regional water supply and resource recovery potential, service level reviews, and system reliability analyses. Resultant white papers from these studies were referenced throughout the plan update process. The 2013 LRWRP included several components related to climate variability, including an analysis of historic water demand (which includes data gathered during past drought periods), a climate-informed water demand forecast, and the consideration of climate variability, amongst other drivers, in a scenario planning exercise.

Understanding historic water demand was a critical component in analyzing potential future changes and developing management strategies. The Town of Cary analyzed historic daily and annual average daily demand, finding distinct seasonal differences. These analyses also showed that water supply and demand can shift drastically in response to drought periods, as it did during several years of record drought (2002, 2007-08), as well as during extremely wet periods. By including drought years in its analysis of historic water demand, the planning team effectively incorporated water shortage supply planning into its Plan.

The Plan included a water demand forecast, which analyzes demand through 2060 based on current municipal programs and policies and through incorporation of uncertainty. Key uncertainty factors integrated into this forecast included: population growth rate, weather-induced annual variability in water use, amount of processed water used in water treatment, amount of non-revenue water, and maximum day peaking factors (which compares water usage on the highest use day of the year with the annual average). This forecast was generated using a Monte Carlo simulation, which helps evaluate the magnitude and likelihood of different combinations of demand scenarios. By including variables influenced by weather and local climate, as well as by using a simulation that helps illustrate uncertainty and variability in demand forecasts, the Town of Cary was able to generate a water demand forecast that incorporates a very basic assessment of how climate may interact with other factors to influence future water demand.

Management strategies identified throughout this planning process were screened through a scenario planning exercise. Climate variability, namely the potential for increased extreme events and associated costs, was one component analyzed in this exercise, along with different economic/business, technology, and societal/political scenarios. Participants determined that increasing climate variability would likely lead to shifts in water supply and pricing, in turn creating more aware and educated consumers who acknowledge and respect water as a finite resource and who adjust their consumption behavior based on this understanding. Based on these variable future scenarios, the planning team added several strategies to its previously established shortlist to enhance the overall resilience of its final Plan.

All strategies identified and developed through the planning process were then prioritized and grouped, culminating in five resultant key strategies dealing largely with water supply, land use and master planning, and increasing best management practices. The five strategies include:

  1. Increase water supply via Jordan Lake allocation
  2. Increase water supply and/or storage by other means (i.e. Crabtree Creek, Cape Fear River, Kerr Lake)
  3. Increase water supply and/or storage via interconnections (e.g., implementing long-term water purchase agreements with other utilities in the region)
  4. Implement integrated master planning and strategic utility resource utilization (i.e. integrate community planning, water resources management, utility planning, and sustainable development)
  5. Promote best management practices (e.g., optimize internal operations, manage customer demands for improved efficiency, utilize reclaimed water)

These strategies were then translated into a water resources portfolio, which outlines a collection of potential strategies than can be used to meet outlined goals and to address challenges identified though water forecasting and scenario planning. The final Plan outlines actions to be taken through 2060, and includes an implementation plan, which calls for expanded water treatment and supply sources by 2023 and 2032, respectively.

Outcomes and Conclusions

In developing the LRWRP, the Town was both hindered and assisted by available data. Downscaled climate models were used to explore possible future conditions, but results from these models were highly inconsistent and provided little guidance at the smaller spatial scales required for municipal planning. Similarly, the planning team recognized the lack of local specificity in current precipitation data. In the face of these data gaps, the planning team chose to plan for variability in order to ensure resilience, acknowledging that projections and associated management responses can be adjusted as more refined models and data become available. Comparatively, other readily available data – including stream gauges, drought indicator wells, and lake inflow data – has helped the utility better understand and plan for future water supply and shortage periods.

The Town published the Long Range Water Resources Plan in 2013. Since publication, the Town of Cary has moved forward with implementing various strategies and actions. Implementation of the suite of actions identified through this process will help the Town of Cary maintain stable water supply into the future and enhance the overall resilience of the Town’s water resources. For example, the Town of Cary is promoting interconnections with other water system suppliers in the Jordan Lake Water Supply Partnership. Diversification of water supply sources enhances supply reliability and provides redundancy during extreme events such as droughts. Cary is also engaging in customer education and outreach surrounding water use efficiency, because the town believes having an educated and aware consumer base will increase public responsiveness and the effectiveness of conservation measures during drought or other water shortage periods. In addition, Cary developed a Water Shortage Response Plan to be activated during periods of acute or chronic water shortage. This plan includes a hydrologic modeling demonstration, demonstrating that in a severe water shortage scenario (i.e., where reservoir inflows to its main water source, Jordan Lake, were decreased by 36% on a daily basis over the 74-year period of record in the model), implementing its water shortage response plan would allow the Town to preserve 50 days of its available water supply under projected 2030 demands. By comparison, if the same conditions occurred and the Town had no water shortage plan in place, consumers would use up all available water, resulting in a water crisis. The Town is also monitoring its ability to supply water to customers, and looking specifically at how interconnections with other water systems can be used to supplement Cary’s water supply in case of a local system failure. These actions, along with others presented in the LRWRP portfolio, will be reevaluated in five years, ensuring that the Town of Cary has a water supply plan that reflects the most current conditions.


Reynier, W., & Gregg, R.M. (2017). Long-Range Water Supply Planning in the Town of Cary, North Carolina [Case study on a project by the Town of Cary Water Resources Department]. Product of EcoAdapt's State of Adaptation Program. Retrieved from CAKE: http://www.cakex.org/case-studies/long-range-water-supply-planning-town… (Last updated December 2017)

Project Contact

Sydney Paul Miller

Water Resources Engineer

[email protected]

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