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7 Assessment of Response Strategies for Specific Facilities and Systems Many facilities and systems in coastal regions will be affected by changes in relative mean sea level. The effects and their im- portance will vary substantially depending on the type of facility and its location. Some structures on the exposed ocean coast are designed to prevent or decrease relatively long-term erosion, to protect buildings, roads, and other facilities during intervals of severe cyclic erosion, or to create wider beaches. These systems have been previously addressed. This chapter considers airports; levees and canals; seaports; port structures; navigation channels, turning basins, clocking areas, and navigation gates; piers and wharfs; ciry and wet docks; highways, railroads, vehicular tunnels, and bridges; storm drains, pipelines, and upstream water quality systems; flood control; commercial and industrial buildings; power plants and associated cooling water systems; hotels and mans; and residential centers. In the design, construction, and utilization of many of these facilities, a Working and economic lifer of 50 years or less is commonly considered. However, functional needs change, facili- ties wear out, and equipment becomes obsolete. Using the three scenarios for relative mean sea level rise discussed in Chapters 1 and 2 of this report results in a range of rise during the next 50 years of about 6 in. to slightly more than 1 ft. The engineering 96

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ASSESSMENT OF RESPONSE STRATEGIES 97 implications of this change would be moderate. For projects with much longer life expectancies, however, there are major engineer- ing implications. Some preliminary studies have examined the effects of a rise in relative mean sea level. For example, the Hawaii Coastal Zone Management Program (1985) studied the effects on Honolulu, Hawaii using four scenarios. For each scenario the report pre- sented a map showing the projected shoreline/wetland line and the location of the present and projected coastal flood hazard zone. Possible erects on the port, the airport, Waikiki Beach, streets, and buildings were also addressed. The study concluded that owing to uncertainties relating to predicted eustatic mean sea level rise: (1) scientific predictive capabilities should be moni- tored, and (2) a meeting should be held in m-1989 to reconsider the situation and make specific recommendations. Some constructed facilities and systems might require the in- stalIation of levees (dikes) to protect them. Experience gained in protecting cities from the ocean in cases of relatively rapid subsidence is valuable. The case study of Long Beach/Terminal Island, California is a good example. More extensive experience has been gained in Japan, where subsidence was caused primarily by groundwater withdrawal. In Tokyo, for example, the cumu- lative subsidence up to 1968 In the eastern section of the city, facing Tokyo Bay, amounted to a magnum of 4.2 m. An exten- sive area became a lowland, with about 115 km2 below sea level. The project reported by Tagarn~ et al. (1970) inclucles 253 km of tide levees, 41 sluice gates, and 9 pumping stations. At the time the paper was written, 75 km of levees had been completed. Another example is Osaka, the second largest city in Japan, situated on the alluvial plain of the Yodo and Yamato rivers. Between 1935 and 1968, the land in the vicinity of the Port of Osaka subsided by amounts ranging from about 50 cm inland to about 250 cm In the harbor area. To protect the city, 124 km of levees were constructed Hong the coast of the bay and on both sides of the rivers running through the city, with a crest elevation of 5 m above datum (the lowest low-water level observed in the port In 1885~. Presently, there are plans to increase the elevation to 6.6 m (Murayama, 1970~.

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98 RESPONDING TO CHANGES IN SEA LEVEL AIRPORTS The airports of many coastal cities are constructed on landfill in bays (e.g., the airports of San Francisco and Oakland, CaTifor- nia, La Guardia Field, New York, and Boston, Massachusetts). Some levees (dikes) used to protect the airports from the bay water are at minnnum elevations and of minimum construction standards, so that a few feet increase in relative mean sea level would result in levee overtopping during severe storms, with the possible breaching of some sections. The degree of the eventual problem is specific to the site. Normal maintenance often requires placing more material on levees to compensate for settlement and consolidation of core materials and foundations. Needed adjust- ments resulting from relative mean sea level rise may be made as a part of this maintenance. A study by the Hawaii Coastal Zone Management Program (1985) concluded that a lift rise in relative mean sea level would result in temporary disruptions of transportation at Honolulu In- ternational Airport; a 4.8-ft rise would cause frequent and pro- Tonged disruptions if no remedial works such as levees were em- placed. Drainage problems exist ~ low-ly~ng airports and will worsen with a rise in relative mean sea level. In addition, there are wet- lands in some airport properties that require pumping and an increase In relative mean sea level would necessitate more pump ing. However, In such cases, conflicts of interest may arise between airport authorities and other agencies, such as the U.S. Wildlife Service. LEVEES Existing Decrees Many miles of levees along bays and tidal rivers would be affected by a rise in relative mean sea level. One example of present hazards to levees is the Sacrament>San Joaquin delta, California (Figure 7-~. According to the California Department of Water Resources (1983b): Since 1980, levee failures have occurred on 12 of about 60 Delta islands. Factors that contribute to levee failures include: instability of the levee section and foundation materials; subsidence; rodent burrows; erosion from wind waves and boat wakes; inadequate

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ASSESSMENT OF RESPONSE STRATEGIES ~ ~ ~ ~ ~ ' k 80,82.83 l ~ ~ ~ J Islet;n ~ ~ Terminous AN run AREAS FLOODED BY LEVEE FAILURE N SINCE 1980 ~ YEAR FLOODED 99 ~ {I ~ .~ I, LODI OCR for page 96
100 RESPONDING TO CHANGES IN SEA LEVEL height (freeboard); seismic activity; and seepage. Flooding of islands can have several adverse impacts, including temporary detriments to water quality due to ocean water intrusion, increased loss of water by evaporation, increased seepage on islands adjacent to the flooded areas, loss of agricultural land, damage to urban and recreational developments, and fish and wildlife losses. A letter of February 13, 1986 from Mr. David N. Kennedy, director of the California Department of Water Resources, indi- cates that since 1980, about $100 million of emergency funds from federal, state, and local sources have been spent shoring up delta levees and reclaiming flooded islands, and that the state Is now furnishing about $2 million each year to improve the levees. It appears that a 1-ft increase In relative mean sea level could have a major impact on the protective capabilities of the levees. Increases in levee elevations (and base widths) should be made if and when needed and justified economically. The added weight of the levees on the soil would increase the rate of subsidence, and this would require design and construction consideration. Earthquake resistance should also be accommodated in seismically active areas. Many of the levees were constructed years ago when it was rel- atively simple to obtain and transport material for their construc- tion. Additional information may be needed to identify problems that could be encountered In the future and to develop poten- tial solutions. Issues include sources and transport of material, environmental conflicts, and requirements for widening the base. Tm some farming areas surrounded by levees, the soil type Is such that the ground level becomes lower with time as a result of farming, wmd erosion, fires, biochemical oxidation, and subsidence due to compaction (Stephens and Speir, 1970~. These effects, combined with an increase ~ eustatic mean sea level, wait change levee stability. Preliminary information from the Delta Levee Subventions Program inclicates that a long-term data collection program Is desirable to measure rates of subsidence (Kennedy, 1986~. Deem measurement compaction recorders may be used to permit the sew oration of surface oxidation and compaction of the peat soil from deeper subsidence resulting from water and/or gas withdrawal. Use of satellite surveying methods is planned to determine ground elevations, since concern exists that much of the data obtained with standard leveling techniques in the past is invalid because of land instability in the delta.

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ASSESSMENT OF RESPONSE STRATEGIES 101 The California Central Valley is quite flat, and the Sacra- mento River is tidal as far upstream as Sacramento. As a first approximation, the levees would have to be increased ~ elevation by the same amount (slightly more in bay areas where deeper wa- ter allows higher waves to be generated) as any increase in relative mean sea level. Gates are an integral component of some levees in the United States; examples mclude the Fox Point Barrier in Narragansett Bay, the New Bedford Hurricane Barrier, the hurricane barrier system at New OrIeans, Louisiana, and the Texas City Hurricane Protection System. Whether a 0.~ to lift rise in relative mean sea level during the next 50 years would require modification of the gates is unknown. Study of the typhoon gates in Japan might provide information concerning this issue. New Levees The construction of new levees may be a solution to protect some densely populated areas from a substantial rise in relative mean sea level. The National Research Council (1983) considered the case of ~ very large rise (5 m) in relative mean sea level for Boston, Massachusetts. This rise ~ much greater than any of the values considered ~ this report, but it is noteworthy that a practice solution may be possible in some Teas. The report states (pp. 473~74~: A rudimentary illustration of the economics can be based on the Boston area. A full 5 m would cover most of downtown Boston. Beacon Hill, containing the State House, would be an island sepa- rated by about 3 km from the nearest mainland. Most of adjacent Cambridge would be awash. But it would take only 4 km of dikes, mostly built on land that is currently above sea level, to defend the entire area. Perhaps even more economical, because it would avoid the political costs of choosing what to save and what to give up and of condemning land for right-of-way, would be a dike 8 or 10 km in length to enclose all of Boston Harbor. If that were done, new deep-water port facilities would have to be constructed outside the enclosed harbor; locks would permit small boats in and out. The Charles and Mystic Rivers would have to be accommodated. Whether in a couple of hundred years there would be any significant Bow in those rivers would depend on changing climate and increasing demand for water. Levees, a diversion canal, or pumping could be compared for costs, and ecological impacts.

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102 RESPONDING TO CHANGES IN SEA LEVEL The study cited above could be redone to determine if any levee would be needed or justified for a 0.5- to I.~ft rise during the next 50 years. The dike length of 8-10 km mentioned in the above study Is very small compared with existing levees in Tokyo and Osaka, Japan. Major problems wall be associated with new levees, including band condemnation, sources and transportation of construction material, and environmental conflicts. In addition, navigation gates may be needed in some regions. S1DD=ENTATION O1? SEAPORTS AND HARBORS, NAVIGATION CHANNELS, TURNING BASINS, AND DOCKING AREAS ~ a Marine Board document (NRC, 1985a), it is stated that there are 102 ports In the United States serving oceangoing traffic (defined arbitrarily as 30 It or more in depth). Twenty-s~x of these are primarily shoreline or coastal, 55 are ~ estuaries, and 21 are basically river ports (not entirely exclusive categories). No pattern of equivalence was found to exist among the ports and harbors. Each has its unique set of conditions of topography, bathymetry, tides, current and wind variations, temperature and climate, salinity and turbidity, ~d sediment transport regimes, which, with the man-made developments, result in a different situation for each case. Changes in tidal and other currents wall occur with changes in relative mean sea level, and changes in tide range and phase may occur. These may, in turn, cause changes in siltation. Hydro- graphic surveys will be required, and changes made in bathymetric charts, tide tables, and current tables. The alteration of seiching conditions could be locally signifi- cant. Wherever the coastline tends to focus long waves of a certain period in the manner of a lens, a rise in sea level may produce dim proportionately increased seiche heights. New resonant locations may develop, and old ones disappear. The effects of these changing conditions on moorings and cargo handling need to be studied. One of the findings of the Marine Board (NRC, 1985a:5) is It is possible that major improvement in dredging will increase deposition rates in certain locations within a harbor rather than reducing the problem. This is because deepening certain channels, especially in estuaries allows seawater intrusion farther upstream

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ASSESSMENT OF RESPONSE STRATEGIES than before dredging, which can cause deposition of fine sediments (which normally would be carried seaward) in the upper reaches. 103 This statement was made for the case of no sea level rise. What would be the effect of a rise in relative mean sea level? At first glance it Ought be thought that it would result in deeper naviga- tion channels, turning basins, and docking areas than at present, which would result in a decreased need for dredging. This might be true for the short term, but not necessarily in the long term, as is implied by the above statement. Major changes would prob- ably occur in the location of the saltwater wedge, and thus in the location of shoaling of the river channel. Sediment movement up- strea~n would affect the costs of dredging and disposing of dredged material. Because of the complexity of siltation and the high costs of dredging, greater detail is devoted to this issue in this report. Consider some of the effects on sedimentation of a rise of relative mean sea level (recall that there are 55 ports in estuarine environments ~ the United States). As the mean sea level rose after the last Ice Age, the sea invaded valleys along coasts created in the past by Duvial erosion and tectonic processes. Whenever a river draining a valley carried enough sediment to fill the drowning valley at the rate of sea level rise, a river delta developed (e.g., Mississippi River). Very different estuary configurations evolved where there was insufficient sediment to fill the valley as sea level rose. These occurred where the valley was wide, or where the stream car- ried little sediment. The invading sea created large shallow bays that cleepened as sea level rose, as in the San Francisco Bay sys- tem, Delaware Bay, and the Chesapeake Bay. Large, shallow bays provide hydraulic conditions that facilitate sedimentation of riverborne sediments and deposition of sed~rnents brought to the bays during high-flow events. Sediments accumulate at the river deposition sites and gradually extend into the bay (Krone, 1979~. Daytime onshore breezes are typical of estuaries in the sum- mer, and these breezes generate waves on the bays. The ability of waves to suspend sediment increases rapidly with decreasing water depth. Many estuaries are shallow enough that the wave action generated by onshore breezes can suspend deposited material and hold it in suspension while tidal currents circulate it throughout the system. At night, when onshore breezes die, the suspended sediment settles. If it settles where subsequent wave action or tidal

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104 RESPONDING TO CHANGES IN SEA LEVEL currents resuspend it, it continues to circulate and may continue to the sea. Under these conditions the upper bays fill to the level where, over time, suspension by wave action equals the supply of riverborne sediment (Krone, 1979~. The supply of riverborne sediment has typically increased with land development. For example, sediment supply to the San Francisco Bay system was vastly increased from the 1850s to 1877 by extensive hydraulic mining in the Sierra Nevada foothills. About 1.9 billion y33 of material deposited in the upper bay Peas of the San Francisco Bay system (Gilbert, 1917), which filled to the level at which wave action maintained the water depth. Sea level has risen about 0.7 It since the hydraulic mining era. Sediment supply after this period apparently continues to be greater than that prior to 1850, and the upper bay areas are shallow, so that the deposition is limited by wave action. The extent of the deposit continues to progress toward the estuary mouth (Krone, 1979~. Another consequence of sea level rise in drowned valleys Is the development of marshes along the shore (Krone, 1985~. Ex- amination of historical sea levels shows that the rise has not been continuous, but has fluctuated through tune. Along the shore of a bay, tidal Hats that developed during a period of higher sea level are exposed for a greater portion of the tidal cycle when sea level temporarily falls. Some types of plants become established on these mud Bats when they are slightly above mean tide level. Plants trap suspended sediment when they are inundated by tides and reduce erosion by waves, so that the rate of sedimentation on the marsh Is enhanced. The elevation of the marsh surface rises rapidly, gradu~ly slowing as the increasing elevation reduces the frequency and duration of flooding by the tide. Depending on the rate of sea level rise and the supply of suspended sediment, the marsh surface tends to maintain its level relative to the tide as sea level rises. The rising marsh surface caused the marsh to invade land where the shoreline slope ~ gradual, and over time extensive marshlands developed. Such marshes were significant traps for suspended sediment and undoubtedly affected the rates of depo- sition in the bays. In developed countries many estuary marshes have been diked for use as salt evaporation ponds or filled for agri- culture and urban development, and thus no longer play a part in estuarine hydrology. Enough information to calculate the loss of

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ASSESSMENT OF RESPONSE STRATEGIES 105 sediment to marshes has only recently become available, and such calculations should be reported in the near future (Krone, 1985~. Changes in relative mean sea levels will also change the geome- tries of rivers flowing into the ocean. Laboratory studies (Chang, 1967) led to the conclusion that rising sea level at the downstream end of a river will greatly enhance the river's meandering ten- dency. FaDing sea level encourages the river to run straight and can significantly increase its sediment-carrying capacity, and thus increase estuarine sedimentation. This phenomenon was reported by geomorphologists studying water-surface fluctuations of large lakes. Whether in an estuarial environment or not, coastal harbors will experience different effects of a change in relative mean sea level, depending on shoreline and bay bathymetry configuration. These changes can be quite complex, but estimates of them can be made with appropriate physical and/or mathematical models. BREAKWATERS, SEA WALLS, AND JETTI1 :S Sea defense systems of the rubble-mound type can be easily increased in elevation by among armor units, stone or cast con- crete shapes. Normal maintenance often requires adding material to compensate for settlement and consolidation of the core mate- rials and foundations, and adjustments for sea level rise may be part of that process. The core of a rubble-mound breakwater is usually relatively impervious. Thus, a breakwater that neecis to be increased in height will require modification to the core, to the filter layers, and to the armor. In seismic regions the new design must be analyzed to assure its earthquake-resistance capacity. Breakwaters and sea wails of solid construction, such as mono- lithic concrete, will be overtopped more often. Since wave damage is a function of wave height, which in turn increases in proportion to water depth, the damage may increase exponentially with sea level rise. This may require raising top levels and slopes after a period of years. ~ some regions the design wave for breakwaters (and levees) is limited due to the water depth so that an increase in water depth owing to a relative increase ~ mean sea level will result in a larger design wave, which will require modification to the size and/or slope of the breakwater.

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106 RESPONDING TO CHANGES IN SEA LEVEL NAVIGATION GATES Navigation gates are covered briefly under the section entitled "Levees.~ Adequate data are not available to determine where new navigation gates might be needed, and if existing gates need to be modified. PIERS AND WHARVES If the sea level at a pier or wharf were to rise as much as 1 It ~ 50 years, and the design life is taken to be 50 years, then the deck elevation may have to be designed to be functional for both present and future conditions. One solution, for which there is precedent at the Brooklyn Navy Yard (where crane rails were built at elevations that allowed for subsidence), is to build at a level 6 in. higher than presently needed, thus splitting the difference. If wave action is expected to be significant, the underside of the deck structure may have to be kept above future wave crests, or 1 It higher than is needed now. Piles or caissons would have to be 1 It longer. Similarly, cranes and loading/unio~ing equipment would have to be designed to reach 1 ft higher above ship decks. Piers are located on open coasts as well as harbors. The case of piers on the open coast would be more complex than discussed above. With no change in the bottom, the piers in most exposed locations would be subject to larger waves as sea level rose, because the deeper water would permit higher breakers, and thus greater wave-induced forces on structures. However, as previously discussed, changes wiD occur in the bottoms, and then the problem becomes quite complex. It is possible that the change in climate, with the resulting change in numbers ant} intensity of storms, will be more impor- tant than a small change In relative mean sea level. For example, during the winter of 1982-1983, when an E! Nino-Southern Oscil- ration condition existed, both the number and intensity of storms increased (Seymour et al., 1984~. More than 12 ocean piers in Cal- ifornia were either destroyed or severely damaged. It is not evident to this committee whether the numbers or intensity of storms will increase or decrease as a result of the greenhouse effect. How- ever, by and large the expected magnitude of the consequences to coastal piers is relatively minor. raters are ~ocarea on open coasts as well as naroors

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108 RESPONDING TO CHANGES IN SEA LEVEL bulk material docks, the vertical travel of the land-based unloader will clear objects on the ships' decks by less and less. Allowance for any increase, in ah cases, will be difficult to compensate, and it may be advisable to incorporate anticipated sea level rise in the original design, despite additional cost. Fluid loading and unloading docks that depend on jo~nted-pipe loading arms also will need to be designed for the rising level of ships' decks and manifolds, since tankers ride higher in the water when they are empty. Loading systems that use hose connections may have more flexibility, or may be more easily modified by adjustments in hose length or supports. HIGHWAYS, RAIIROADS, BRIDGES, AND VEHICULAR TUNNELS As sea level rises, highways and railroads across lowlands near tidal water wiD experience more frequent flooding during high tides and storms. This effect may be especially severe in certain estuaries where the rise in sea level will be amplified, the more so because these same estuaries are more vulnerable to storm surges as water funnels into a gradually narrowing arm of the sea. The levels of such highways and railroads may have to be raised by reballasting or adding pavement from time to time. Some highways and railroads already experience flooding during heavy rains and high tides, aIld these events would increase, especially at underpasses. Increased pumping capacity would be needed. Much can be learned from experiences ~ Japan with the rapid subsidence of some heavily populated areas that have much infrastructure of this type. The clearance above high water will gradually diminish for bridges across water in the tidal zone. The amount of the reduction will be greater in the case of bridges upstream in estuaries where the rise of water level is amplified by funnel ejects, as in Delaware Bay. Although the rise may be slow and gradual, the consequences of damage to a bridge may be so catastrophic as to warrant regular monltormg. The clearance between the center of a suspension bridge and the water surface depends upon mean sea level, tide stage' tem- perature, winds, freshwater flow into an estuary, and static and dynamic loads on the bridge. An example of how elevation can be affected by structural changes in the bridge is the Golden Gate

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ASSESSMENT OF RESPONSE STRATEGIES 109 Bridge over San E`rancisco Bay, California. About three decades ago a lower lateral bracing system and maintenance platform rails were instated, resulting in a downward deflection of about 3 It from the original dead-Ioad position at the mid-point of the cen- ter span. Recently, a lighter-weight deck element was installed. The maximum additional camber of the center span during the replacement operations was about 7 ft and occurred when the new lighter-weight deck had been placed on the Marin backspan and the mainspan, with the heavier original concrete deck on the San Francisco backspan (D. E. Mohn, Golden Gate Bridge, Highway, and Transportation District, San Francisco, California, letter, De- cember 11, 1986~. COMMERCL\[ AND INDUSTRIAL BUIIDINGS Structures near tidal water will suffer increased flooding. Sur- face water levels will rise, and groundwater levels, which generally are driven in part by nearby harbor and estuary levels, will fol- low with a time lag and amplitude that increase and decrease, respectively, with distance. Results are likely to be increased seepage into basements, poorer storm drainage, and ponding in parking areas and am preaches. The former may be countered with better waterproofing or by sump pumps and drainage; the latter may eventually require added paving. POWER PLANTS Most power plants on coasts use sea water for cooling, and power plants on estuaries use estuarine water for cooling. Studies should be made of the effects of rising relative mean sea level on these facilities. The "design lifer of a power plant is about 40 years, a period over which mean sea level could vary from a few inches to almost 1-ft, considering the scenarios used in this report. Engineering changes required in those aspects of operation most affected by a 1-ft rise in relative mean sea level, such as cooling water intake and discharge systems, would be handled as normal changes. Environmental effects would also need to be considered

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110 RESPONDING TO CHANGES IN SEA LEVEL PIPELINES With rising sea levels, groundwater might rise above some pipelines in cities and ports, affecting corrosion rates. Large diameter pipes are used in sewer outfalis in many coastal cities and, in some cases, for intake and discharge conduits for power plant cooling water systems. To counter the effects of sea level rise in these systems, it might be necessary to increase pump ing capacity, as well as to increase the capability of outfall systems to dilute their effluent. Another possible effect is associated with the amount of ero- sion that knight occur on sand coasts. Pipe sections buried under the beaches and current surf zone might become exposed, while discharge ports could become covered with sand. FLOODING AND STORM DRAINS Flooding could be a major problem ~ many low-ly~ng por- tions of coastal cities with a sea level rise. Examples include New Orleans, portions of which are below present sea level, and areas of San Francisco. Additional pumping will be required. More flood- ing would occur than at present in many areas, and levees, tide gates, and channels would be needed in some regions. Environ- mental conflicts would have to be exarn~ned and reconciled. Considerable detail on planning and installation of a flood control system for the Koto delta region of Tokyo, Japan is given by Ukena et al. (1970~. Because of subsidence, about 50 percent of the Koto delta area became lower than the daily low-tide level by 1953. Natural runoff from this area became nearly nonexistent, and forced drainage had to be used on a very large scale. Subsidence in lands adjacent to the south end of San Francisco Bay between 1934 and 1967 was measured at several hundred benchmarks. About 100 ran subsided more than 3 ft. with the magnum subsidence of about 8 ft. As a result, several miles of levees were raised to prevent flooding by bay waters, and flood control levees were added near the ends of the streams running into the bay (Poland, 1970~. Poland states that salt water from the bay moved upstream, and channel grades crossing the subsidence area became downwarped. This resulted in sediment deposition near the stream mouths, with a reduction in channel capacity, which in

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ASSESS OF RESPONSE STRATEGIES 111 turn required an increase ~ levee heights. Even with the higher levees, flooding occurs at tunes of very high runoff. Williams (1985) points out that at present there are no stan- dard assumptions for backwater calculations in the design of flood control projects; the usual practice is to design for the Goodyear flood at a title level of mean higher high water. An increase in rel- ative mean sea level could result in higher flood waters upstream, with the possibility of levee overtopping. In addition, he states that the flood control systems of many areas presently rely on storage of flood waters and gravity releases at low tide. Inade- quate information is available to see how a rise in relative mean sea level would affect specific areas. In some parts of the country (for example, the New Jersey Meadows tidal marsh), mosquito control commissions have in- stalled elaborate systems of drainage ditches and tide gates to Intuit backflood~ng of marshland when the tide rises. The flow is very sensitive to changes in mean tide level, and will be affected seriously by a rise in relative mean sea level. La Roche and Webb (1986) est~rnate the cost of the expected overhaul of an urban gravity drainage system in Charleston, South Carolma for (1) present sea level, (2) an 11-~n. rise, and (3) a 1~. rise. They also estimate the cost of an overhaul if the system is built for today's sea level and later retrofitted for 11- and lawn. rises. Presently, designing for an 1l-iIl. rise would require larger pipes at an additionad cost of $260,000 (a 5 percent increase). However, a retrofit would cost $2.4 Bullion not including indirect costs of closing the streets. Waddell and Blaylock (1987) conducted a similar evaluation for a watershed in Ft. Wadton Beach, Florida, which is more lightly developed and employs a variety of independent measures to reduce flooding. They conclude that there are no savings to designing the system for a future rise, compared with upgrading the system if and when a rise occurs. Titus et al. (1987) evaluate the planning implications of the preceding studies. They conclude that future sea level rise is rele- vant to today's design decisions where cities are overhauling urban gravity drainage systems, but not where drainage improvements are achieved by new parallel systems. In the former case, designing for a future rise is similar to insurance, with the economic mer- its being site specific. The report also discusses forced drainage, which was not investigated in detail by the studies.

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112 RESPONDING TO CHANGES IN SEA LEVEL A segment about 30 km Tong by 7 km wide along the coast of the Sea of Japan in Nilgata and the nearby vicinity subsided by about 50 to 150 cm between 1959 and 1968 (kimono, 1970; Takeuchi et al., 1970~. Larger areas subsided by lesser amounts; most of the Niigata Plain, about 8,300 km2, had some subsidence. Takeuchi et al. (1970) mention that in the Nugata lowland on the flood plain of the Shinano River, the subsidence decreased the ability of pumps to drain the area and also damaged the drainage canal network. They estimated the cost of reconstruction to be about 20 billion yen (then about $56 million). HOTELS AND WILLIS The effects of a sea level rise on these facilities will be similar to those for commercial buildings, but greater emphasis wall be needed to preserve the amenities that attract patronage. Remedies may be applied sooner as the effects of even a small rise in sea level become apparent. This may be especially pertinent for facilities close to the oceans. The threat of damage to a waterfront hotel, for example, might warrant extensive measures to reinforce sea wails, add beach materials, or otherwise protect the shore and hose! foundations from storm damage. Many mass and hotels in the United States become "aged" in a few decades and undergo major and extensive renovation. It Is likely that measures to accommodate small rises ~ relative mean sea level would be taken as a part of the renovation. RESID1:NTL\L CENTERS As more and more people move to shore housing sites, a rise in sea level will become more evident to greater numbers of people. The effects wait be most noticeable In beach erosion, sea wall damage, and flooding of lower levels, drives, and swales. Since many such areas are also subject to subsidence from earth compaction, groundwater pumping, or tectonic movement, the effect of the rise may be accentuated. For example, in the area around Baytown, Texas, on Galveston Bay, subsidence has caused frequent high-tide flooding of land that slopes toward the bay at gradients of 1 ft/mi, on the average.

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ASSESSMENT OF RESPONSE STRATEGIES WAT1:R SUPPLY SYSTEMS 113 A number of effects on water supply systems (particularly on water quality) can be realized with changes ~ relative mean sea level. Some of these are considered below for both groundwater and surface-water sources. Perched Mesh Water The increase in hydrostatic pressure with depth is about 3 percent greater in sea water than In fresh water. If the surface of the freshwater table is X feet above mean sea level, under static conditions, the freshwater-seawater interface would be about 40X It below mean sea level. As sea level rises, this "bubbles of fresh water should simply float In the salt water at an elevation that is higher by the amount of sea level rise. Thus, no significant effects are expected. Addi- tionally, in many locations on barrier spits and islands the water supply is presently brought from other regions and thus a rise in sea level should present no additional problem. Aquifers Coastal aquifers normally flow toward adjacent surface waters such as lakes, rivers, estuaries, or the sea. Excessive pumping for irrigation and municipal water supplies can reverse the flow so that water is recharged to the aquifer. If such recharge occurs near the mouth of a river, a rise In sea level can recharge the aquifer with sea water. Conditions are aggravated during droughts, when the saltwater wedge advances upstream and when pumping for irrigation is augmented. An example of a potential problem is the Delaware River, which recharges the Potomac-Raritan-Magothy aquifer (the source of water for many wells in New Jersey) above river mile 98 (Hull and Titus, 1986; Camp, Dresser and McKee, Inc., 1982; Hull and Tortoriello, 1979~. Some possible engineering responses to this problem are: (1) modifying the elevation of the aquifer's connection to the estuary to reduce the landward penetration of the salt wedge; (2) reducing the permeability of the sediment where the aquifer communicates with the estuary to reduce the rate of seawater recharge; and (3) increasing recharge during periods of high precipitation.

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114 RESPONDING TO CHANGES IN SEA LEVEL Freshwater Intakes prom Upstream Regions of Estuaries A rise in relative mean sea level could have far-reaching effects on taking fresh water from upstream regions ~ estuaries. As an example, consider the Sacramento-San Joaqum delta region of California from the standpoint of maintaining water quality standards. The California Water Resources Control Board (1983 and 1984) has stated: The Delta is a vital link between river systems of the Sacramento Valley and the water deficient areas to the south and west of the Delta. Two major systemsthe State Water Project (SWP) operated by the Department of Water Resources (Department) and the federal Central Valley Project (CVP) operated by the United States Bureau of Reclamation (Bureau) withdraw supplies from the Delta for use in areas of need. These projects are the two largest water diversions from the Delta. They provide municipal supplies to areas where over 14 million people live and support an extremely productive agricultural economy in the San Joaquin Valley. The underlying principle of these standards is that water quality in the Delta should be at least as good as those levels which would have been available had the state and federal projects not been constructed, as limited by the constitutional mandate of reasonable use. The standards include adjustments in the levels of protection to reflect changes ~ hydrologic conditions experienced under different water year types. In a recent decision of a state court of appeal, it was ruled that the California Water Resources Control Board has "compromised its important water quality role by defining its role too narrowly in terms of enforceable water rights (Einstein, 1986~. A possible rise of mean sea level of between 0.5 and 1.5 m by the year 2100 could have an important imp act on the struc- tures and methods necessary to maintain water quality standards. According to Kennedy (1986), there are many alternatives to transferring fresh water through and around the delta; several are described by the California Department of Water Resources (1983a). In the Ned' York Times (March 21, 1986), a newly developed scheme was announced to liberate New York City from the periodic water shortages that result from its dependence on the drought- prone tributaries of the Delaware River. An existing pump station on the Hudson River at Chelsea, on the east bank near Poughkee~ sie, would be enlarged and integrated into a plan of new reservoir

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ASSESSMENT OF RESPONSE STRATEGIES 115 construction. During high-discharge stages of the river, the fresh water would be ~skimmed" and put in the storage reservoirs. At Tow-discharge times the salt water comes dangerously close to the pump station. At present, the Hudson River is tidal as far as Albany. A sea level rise of 0.5 m would bring the saltwater wedge above the level of Poughkeepsie. Hull and Titus (1986) estimate an increased salinity of the Delaware estuary during a repeat of the 1960s drought for 2.4- ft and 8.2-ft rises in sea level. A 2.4-ft rise would cause the 25~ppm isochIor (the desalt frontal to move 7 miles upstream, on the average. During 15 percent of the tidal cycles, the river at Philadelphia's Torresdale drinking water mtake would have elevated sodium concentrations exceeding 50 ppm (the New Jer- sey drinking water standard) if no countermeasures were taken. Lennon et al. in HuD and Titus (1986) conclude that the elevated salt levels in the river could contaminate parts of the Potomac- Raritan-Magothy aquifer, which is pumped at a point below sea level and recharged by the river. The report cites several mitiga- tion measures, such as new reservoirs, and recommends long-term planning for consequences of sea level rise as well as possible changes ~ drought frequency caused by the greenhouse effect. LANDPII`LS AND WASTE DISPOSAL SITES A rise in sea level can affect landfills and disposal sites in two ways: (1) direct overtopping and erosion, or (2) changes in the level of the aquifer and the groundwater leaching pattern. Dikes, similar to those currently used in some containment areas, could be designed and constructed to counter both of these effects. OFFSHORE PLATFORMS AND ARTIFICL\[ ISLANDS The productive lives of offshore platforms and artificil] islands used ~ the production of oil and gas is on the order of 25 years. They should not be affected very much by eustatic rise in mean sea level In that time span. The problem of relative rise in mean sea level owing to subsidence can be of much greater importance. An article in News of Norway (May 22, 1985) describes how the Ekofisk platforms have sunk 2 m (6 ft) and continue to subside at a rate of 1 - cm/mo or 12~8 cm/yr (about 5-9 in.~. The article mentions a conclusion in a recent report by the Norwegian

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116 RESPONDING TO CHANGES IN SEA LEVEL classification society, Det Norske Veritas, that several platforms on the field would be total losses in the event of a major storm. An article in the Financial Times of London (April 11, 1986) states that a massive rescue plan has been proposed to raise six steel of! platforms by 6 m. It claims the platforms have sunk nearly 3 m because of the weight of 3,000 m of rock overlying the field's oil ant] gas reservoir. Subsidence due to the removal of hydrocarbons is also a likely contributing factor. A report commissioned by Phillips Petroleum to study two of the peripheral platforms in the field concluded that total loss, given a Goodyear wave, could not be ruled out if the platforms sank 8.5 ft. and even a heavy storm would cause serious damage. A number of alternatives were considered. The lowest cost alternative, and one which could be done with only 18 days production shutdown, would cost $286 million (Anonymous, 1986~. The plan would consist of jacking up the decks of the platforms and installing extensions. The work is expected to start in June 1987.