Greenhouse Effect, Sea Level Rise, and Salinity in the Delaware Estuary
Greenhouse Effect, Sea Level Rise, and Salinity in the Delaware Estuary (PDF, 44 pp., 1.1 MB, About PDF) , was a joint report from the US Environmental Protection Agency and the Delaware River Basin Commission, edited by C.H.J Hull and J.G. Titus (EPA 230-05-86-010). The report's Summary and Conclusions are available below. For quicker reading, an html version is also available
For additional reports focused on the implications of rising sea level, go to the Climate Change Site's Sea Level Rise Reports section.
Summary
Increasing atmospheric concentrations of carbon dioxide and other gases are expected to warm the earth a few degrees (C) in the next century by a mechanism commonly known as the "greenhouse effect." Such a warming could alter precipitation patterns and raise sea level. Although it is not yet possible to predict whether particular areas will receive more or less rainfall, there is a general agreement that sea level will rise. Unfortunately, estimates for the year 2025 range from 5 to 21 inches above current sea level, while estimates of the rise by 2100 range from 2 to 11 feet.
Several issues must be resolved for society to rationally address the possibility of significant changes in climate and sea level. Officials making decisions about near-term projects with long lifetimes must examine the potential consequences and determine whether these risks justify a shift to strategies that are less vulnerable to changes in sea level or the frequency or severity of droughts. Research officials must assess the opportunities for improving predictions and decide whether the need for these improvements justifies accelerating the necessary research. Decision makers must decide whether to base policies on today's inadequate knowledge or ignore the implications until they are more certain.
One potential impact of a global warming and rise in sea level would be an increase in the salinity of estuaries, which might threaten drinking water and aquatic ecosystems. The Delaware River Basin Commission (DRBC) has long considered the implications of droughts on management of water resources in the Delaware estuary; since 1979, it has also considered the implications of recent sea level trends. However, the DRBC has not previously focused on the possibility that the "greenhouse warming" could exacerbate salinity problems. The Environmental Protection Agency has initiated studies on the impacts of sea level rise and climate change on erosion, flooding, and wetland protection, but has not previously examined the impacts on salinity.
This joint report by the Environmental Protection Agency and the Delaware River Basin Commission examines the implications of the greenhouse warming for salinity control in the Delaware estuary. The study focuses on the implications of (1) a 21-inch rise in global sea level expected by 2050, which would imply a rise of 2.4 feet in the Delaware estuary; and (2) a 7-foot global rise by 2100, which would imply an 8.2-foot rise in the Delaware estuary. The authors estimate the increase in estuary salinity, estimate the possible increase in salinity of the Potomac-Raritan-Magothy aquifer system, discuss the implications, and examine possible responses. Potential changes in precipitation are not evaluated.
Conclusions
- Sea level rise could substantially increase the salinity of the Delaware estuary in the next century. If no countermeasures are taken, a repeat of the 1960s' drought with a 2.4-foot rise would send the salt front upstream to river-mile 100, compared with mile 93 for current sea level. Moreover, the chloride concentration at mile 98, the DRBC salinity control point, would increase from 136 parts per million (ppm) to 305 ppm. An 8.2-foot rise would send the salt front upstream to mile 117 and would increase salinity to 1560 ppm at the salinity control point.
- Accelerated sea level rise could cause excessive salinity concentrations at Philadelphia's Torresdale intake if no countermeasures are taken. For a 2.4-foot rise, sodium concentrations would exceed 50 ppm (the New Jersey drinking water standard) during 15 percent of the tidal cycles during a recurrence of the 1960s drought. For an 8.2-foot rise, sodium concentrations would exceed 50 ppm during 50 percent of the tidal cycles.
- Accelerated sea level rise could threaten the New Jersey aquifers recharged by the Delaware River. During the 1960s drought, river water with chloride concentrations as high as 150 ppm recharged the Potomac-Raritan-Magothy aquifer in the vicinity of Camden, raising chloride concentrations of some wells from 20 ppm to 80 ppm. A repeat of the 1960s' drought with a 2.4- foot rise in sea level would result in river water with concentrations as high as 350 ppm recharging the aquifer in this area. During the worst month of the drought, over one-half of the river water recharging the aquifer would have chloride concentrations in excess of 250 ppm. With an 8.2-foot rise, 98 percent of the recharge during the worst month of the drought would have chloride concentrations greater than 250 ppm, and 75 percent of the recharge would be greater than 1000 ppm. (The EPA drinking water standard is 250 ppm, and water with chloride concentrations greater than 78 ppm generally exceeds the 50-ppm sodium standard.)
- Planned but unscheduled reservoirs could offset salinity increases expected in the next forty years. Salinity increases resulting from a one foot rise in sea level expected in the next forty years would require increased reservoir capacity of at least 110 thousand acre-feet. However, reservoirs planned by the DRBC but not yet scheduled would have a combined capacity of 592 thousand acre feet.
- Possible shifts in precipitation resulting from the greenhouse warming could overwhelm salinity increases caused by sea level rise. Excessive salinity has been a problem only during droughts. Unfortunately, it is not possible to determine whether the Delaware River Basin will receive more or less rainfall in the future. A recent study by NASA suggested that a tenfold increase in drought frequency cannot be ruled out. On the other hand, some researchers have suggested that most coastal areas will experience a 10 percent increase in precipitation.
- Uncertainties regarding future climate change do not necessarily imply that waiting for better predictions is the most prudent strategy. There is no guarantee that accurate climate projections will be possible when they are needed. Moreover, some measures may have potential benefits so far in excess of their costs as to be warranted in spite of current uncertainties. For example, identifying potential reservoir sites long before they are necessary and not developing them for other uses can ensure that they are available if and when they are needed, without imposing substantial costs. Waiting until they are needed could result in no satisfactory sites being available.
- A regional study should be initiated that examines the potential impacts of precipitation changes as well as sea level rise for the Delaware estuary and adjacent river basins. A thorough understanding of the water resource challenges faced by the Delaware River Basin is not possible without considering the needs of New York City and other areas outside the Basin that depend on the Delaware for water supply.
This document has been reviewed in accordance with the U.S. Environmental Protection Agency and Delaware River Basin Commission peer and administrative review policies and approved for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. Please send comments to James G. Titus, Strategic Studies Staff, U.S. Environmental Protection Agency, Washington, D.C. 20460.