Drought, drinking water, and the worth of a creek

Posted February 10th, 2014 by Sylvia S Tognetti and filed in Ten Mile Creek
Two Line Salamander found in Ten Mile Creek. Photo Credit: Cathy Wiss, Audubon Naturalist Society.

Two Line Salamander found in Ten Mile Creek. Photo Credit: Cathy Wiss, Audubon Naturalist Society.

I have recently become involved in an effort to save Ten Mile Creek, also known as the last best creek in Montgomery County (MoCo) Maryland. MoCo even uses it as a ‘reference stream’ against which to measure the health of other streams, which means you can still find salamanders in it, and even a few trout. Not surprisingly, it is now threatened with development impacts. These are associated with a Master Plan for the Clarksburg area, for which the MoCo Council is considering options for a limited amendment that would establish the permissible amount of impervious surface in the watershed, for purposes of protecting the Creek.

It just so happens that this creek is also the cleanest source of water for a reservoir that was built in response to the drought of 1966, to augment the flow of the Potomac River during such events. That makes the reservoir an emergency drinking water source, not only for MoCo, but also for much of the Washington Metropolitan Area. As of 1982, the main public water authorities in MD, DC, and VA (WSSC, DC Aqueduct and Fairfax Water) have actually collaborated in the building and ongoing management of this reservoir and another larger one further away in West Virginia. These two reservoirs are jointly managed as an alternative to a plan that had been proposed by the Army Corps of Engineers to build 16 of them.

In presentations to the MoCo Council, the MoCo Planning Board has generally conceded that if development activities go forward at proposed levels of imperviousness, Ten Mile Creek would lose its status as a reference stream, which will make it more difficult if not impossible to find salamanders and trout. But the main question at least some members of the Council seem to have is whether or not the reservoir is really a drinking water source (as is stated on the following sign), and whether or not development in one of its three watersheds poses a threat to it. Also, whether more information is needed to make a decision – perhaps so that it can be put off until after the June primary election.

To the Council’s credit, the responsibility of local government to protect drinking water is not taken lightly. Not coincidentally, there is a large and growing coalition of citizens groups who support full protection of the watershed, and who, among other things, have been telling the Council: “I drink water, and I vote.” [to add your voice, click here]  In addition, three former MoCo public officials, who were involved in the creation of the reservoirs, published an Op-Ed in mid-November which alleges that MoCo is “rolling the dice with the region’s water system.” And last week, the Council received a letter from the Chairman of the DC City Council expressing concern about impacts on the DC water supply.

So last Tuesday (Feb 4), in a committee work session, representatives from WSSC (the water utility that operates the reservoir), and from the MoCo Department of Environmental Protection (DEP) were asked a seemingly simple multiple choice question by the Committee Chair Nancy Floreen: “Would the proposed limited amendment to the Master Plan affect drinking water?” i.e., “are we really rolling the dice?” – as she put it previously. The multiple choices were: yes, no, or, “more information is needed.”  They both said “no.”

In support of his answer, the DEP representative said the reservoir is not classified as impaired under state standards and that it would not pollute the reservoir any more than the other two previously developed watersheds that drain into the reservoir. In other words, it meets standards, at least for now. But he also commented that protecting Ten Mile Creek would protect the reservoir. Unanswered was the broader question of cumulative impacts from all three watersheds, and of protecting the Creek, which is more sensitive than the reservoir. There was more back and forth with the Council President about whether a study of these cumulative impacts should take place before or after a decision – and if after, why bother?

Little Seneca Lake is a Drinking Water Reservoir for the Washington Metropolitan Region.  Photo Credit: Montgomery Countryside Alliance

Little Seneca Lake is a Drinking Water Reservoir for the Washington Metropolitan Region.
Photo Credit: Montgomery Countryside Alliance

Although it is clear that the reservoir is a back-up drinking water source, as the sign says, the significance of its water quality tends to be dismissed because it is indirect. Water from the reservoir first flows to the Potomac River where it gets mixed with all other sources upstream from the intakes to the water treatment facilities. Also, because it is only used in significant quantities during droughts.

If we look at the watershed of Ten Mile Creek from an economic perspective, as providing an ecosystem service, it is fair to ask if reservoir water quality, good or bad, would make a difference that is economically significant at the relevant scale. For drinking water purposes, the relevant scale is the 4.3 million population served by the public water systems in the Washington Metropolitan Area. The difference may well be undetectable during average flow conditions when the reservoir is not used. What has not been addressed by the Council and the agency experts, is the significance of water quality during the low flow/drought conditions for which the reservoir was built, when releases from the reservoir could constitute a larger and more significant percentage of total river flow. However, this issue was raised in testimony to the Council by Scott Fosler, a former Councilmember who was involved in building the reservoir who stated:

The technique of low flow augmentation rests on the assumption that when the water flow in the main source river – in this case the Potomac – gets so low as to significantly lower the quality of water, cleaner water is released from a reservoir to increase the overall flow and essentially dilute the dirty water.   The reservoir system works in part because of “absolute assurance that the two reservoirs would be protected, clean and available when needed.”

The issue was also raised in testimony by Ephram King, a county resident and retired former EPA Director of the Office of Science and Technology, who was in charge of water quality criteria standards and implementation, who stated:

Not only are suspended solids an issue but also nitrogen and phosphorus pollution lead directly to the development of harmful algal blooms… precisely at the time that you want to use the reservoir, at high temperature and low flow drought conditions.

The issue was again raised in the letter from DC Council Chairman Phil Mendelson, which states:

During a drought, water from Little Seneca Reservoir is released to form a significant portion of the Potomac’s flow. Thus, Little Seneca Reservoir is a crucial source of clean drinking water.

It just so happens I found some numbers that allow for a rough estimate of the percentage of flow that would come from the Little Seneca reservoir during record low flow conditions that occurred in the 2002 drought. In that year, releases from the Little Seneca Reservoir occurred on 18 days between July 12 and September 22, with a maximum single-day release of 125 million gallons (Kiang and Hagen, 2003) – which is more than the average amount withdrawn per day by the Potomac Filtration Plant. Adding the lowest flow, 166 million gallons/day (mgd), to the amount of water withdrawn daily for use by all three jurisdictions, 391 mgd, allows for a rough estimate that the amount of water released from Little Seneca would have amounted to between 20 and 25% of the river flow on the days when flow was at or close to the record low. Ten Mile Creek, which appears to be the largest tributary, and therefore over one third of that (~8%), would be the only source of high quality water for purposes of dilution. The percentage could easily go higher if the flow dropped to the minimum of 100 mgd agreed upon to protect the river.

For a visual, see the following figure, which contrasts the total flow during the 2002 drought period with the amount that would have occurred absent the water supply releases from both reservoirs. Given that it takes 8-9 days for water to arrive from the West Virginia reservoir, supply from the Little Seneca reservoir could conceivably be higher for a brief period if there were a sharp unexpected drop in river flow. And although not currently set up for use as a backup in the event of an outage at the water treatment plant, the possibility of using it with only minimal treatment was contemplated by John Menke, who was a member of the MoCo Council at the time – as stated in his testimony to the current Council.


Flow that would have occurred at Little Falls in the absence of water quality and water supply releases augmenting Potomac River flow. Source: Kiang and Hagen, 2003

Flow that would have occurred at Little Falls in the absence of water quality and water supply releases augmenting Potomac River flow.
Source: Kiang and Hagen, 2003

Water quality is closely tied to flow conditions. As a general rule, during low flows, lower levels of sediment and pollutants enter water bodies because there is less runoff but these just build up until the next storm. However, existing pollutants become more concentrated because there is less dilution. With reduced ability of the soils to absorb water, watersheds also become more susceptible to erosion after the drought period (Cummins et al, 2010). Other impacts of low flow are higher temperatures, lower dissolved oxygen, and reduced mixing – particularly in lakes, where lower oxygen zones are likely to remain at the bottom (Delpla et al, 2009). These conditions typically lead to algal blooms and growth of toxic bacteria that can lead to disease outbreaks (Covich, 2009). I recall stronger odors from the river at a riverside picnic during the 1999 drought – somewhere between Great Falls and Little Falls, but prior to the passage of the Clean Water Act in 1972, summer low flows in Washington DC were actually a public health problem (Cummins et al, 2010).

Other issues not extensively discussed in the Council work sessions are the implications of our changing climate, in which both droughts and heavier rainstorms could shift from being extreme to routine events. The drought of 2002 set new record lows. And a study by the Interstate Commission on the Potomac River Basin (ICPRB) concluded that by 2040, the “average total annual stream flow in the basin is predicted to decrease in 14 out of the 18 scenarios, by as much as 35%.” Although there is uncertainty as to whether total precipitation will increase or decrease in the region, warmer temperatures are expected to increase evapotranspiration by 6-8%, which is the equivalent of 1.2 to 2.9 inches of rainfall (Ahmed et al 2010b). At the same time, in the northeastern US, the amount of rain falling in heavy storm events has already increased by 74% between 1958 and 2010 (Horton et al 2013). In addition to aggravating water quality problems that could lead to difficulties and higher costs at water treatment facilities, these changes are likely to lead to increasing rates of erosion and runoff, which would in turn lead to more rapid sedimentation of the reservoir and loss of capacity (Nearing et al 2005). Lastly, increases in impervious surfaces aggravate droughts because this reduces the amount of water that infiltrates into the soil and replenishes groundwater, which sustains stream flow during dry periods.

This essay has made the case for the ecological and economic significance of Ten Mile Creek. Recently, over a thousand hand-written letters supporting full protection of Ten Mile Creek were delivered to Council Vice President George Leventhal, which is one metric of the value of Ten Mile Creek to the residents of Montgomery County.  The question is how protection can most effectively be done, in a rapidly changing context that includes an exploding urban population, uncertain but potentially high costs, and a number of legal and institutional challenges associated with making land use decisions that protect water quality. These challenges include the threat of a lawsuit by at least one of the developers who invested in land in this watershed with the expectation of a Business As Usual zoning decision that would eventually allow relatively high density development to proceed. Ultimately these challenges suggest the need for policy changes at all levels which are beyond the scope of this post but that would enable a more proactive approach to protecting water sources, as well as managing drought and other climate impacts on water resources.

In conclusion, my response to the issues raised in the Council work session:

  • The Council needs to support pursuit of the study of Little Seneca Reservoir recommended to County Executive Leggett in October 2013, by Scott Fosler.  This study should include analysis of the significance of water quality for water treatment during the low flow/drought conditions for which the reservoir was built, when releases from the reservoir would constitute a larger and more significant percentage of total river flow.
  • Widening the geographic scope beyond Little Seneca Reservoir, a study to consider a region-wide strategy to protect water sources and recommend enabling legislative changes at County, State and Federal levels, is also a good idea.
  • But a study is not a reason to  delay of a decision to protect the Creek, which is entirely in the hands of the Montgomery County Council.
Inquisitive Two Line Salamander.  Photo credit: Cathy Wiss, Audubon Naturalist Society

Inquisitive Two Line Salamander.
Photo credit: Cathy Wiss, Audubon Naturalist Society


Covich, A. P. (2009). Emerging Climate Change Impacts on Freshwater Resources: A Perspective on Transformed Watersheds. Washington DC: Resources for the Future. Retrieved from http://www.rff.org/rff/documents/RFF-Rpt-Adaptation-Covich.pdf

Delpla, I., Jung, A.-V., Baures, E., Clement, M., & Thomas, O. (2009). Impacts of climate change on surface water quality in relation to drinking water production. Environment International, 35(8), 1225–1233. doi:10.1016/j.envint.2009.07.001

Horton, R., Yohe, G., Easterling, W., Kates, R., Ruth, M., Sussman, E., … Wolfe, D. (2013). National Climate Assessment Draft Report. Chapter 16. Northeast. U.S. Global Change Research Program. Retrieved from http://ncadac.globalchange.gov/

Kiang, J. E., & Hagen, E. R. (2003). 2002 Drought Operations and Lessons Learned: Washington Metropolitan Area (No. 03-6). Rockville, MD: Interstate Commission on the Potomac River Basin. Retrieved from http://www.potomacriver.org/publicationspdf/ICPRB03-6.pdf

Nearing, M. A., Jetten, V., Baffaut, C., Cerdan, O., Couturier, A., Hernandez, M., … van Oost, K. (2005). Modeling response of soil erosion and runoff to changes in precipitation and cover. CATENA, 61(2-3), 131–154. doi:10.1016/j.catena.2005.03.007