The Effects of Tide Gates on Estuarine Habitats and Migratory Fishish

by Guillermo R. Giannico and Jon A. Souderouder

ikes and tide gates have been used the flow of upland water through creeks or worldwide for several centuries to sloughs into estuaries or rivers. A flood box D drain wetlands, both in estuaries might be as simple as a single culvert running and in the lower sections of rivers, which through a dike wall or as complex as a small, are influenced by tides. Wetland draining bridge-sized, concrete structure that includes has been carried out either to convert lands two or more culverts, deflection wing walls, into agricultural use, to control populations and upstream and downstream pilings (see of mosquitoes and other insects, or to allow figures 1a and 1b). In all cases, doors or lids urban development on low-lying coastal zones are attached to the discharge ends of the (Daiber 1986; Middleton 1999; Doody 2001). culverts to control water flow. These doors In the Pacific Northwest region of North are commonly referred to as tide gates, or America, the draining of estuarine wetlands flap gates (figure 1b). Tide gates close during began approximately two hundred years ago incoming (flood) tides to prevent tidal waters (Dahl 1990). Tidal marshes close to seaports from moving upland. They open during and urban centers have been particularly outgoing (ebb) tides to allow upland water to vulnerable to conversion, with losses of 50 flow through the culvert and into the receiv­ to 90 percent reported for many estuaries in ing body of water. Figure 2 illustrates the Oregon and Washington (NRC 1996). Many entire gate cycle as water levels change. of these marshes have been isolated from Tide gates tend to be effective at main­ the adjacent estuaries by dikes (Frenkel and taining low water levels on the upland side Morlan 1991) and in some cases completely of dikes. Unfortunately, by altering water or partly filled in to accommodate a variety flow they have some undesirable side effects of land uses (for example, agricultural, recre­ that can be classified into three main—but ational, residential, and industrial). In areas interrelated—categories: physical, chemical, like Coos Bay, Oregon, almost 90 percent of and biological. tidal marshes have been permanently lost to The physical effects of tide gates in­ dikes and landfills (Schultz 1990), and in parts clude elimination of upland tidal flooding of Puget Sound, Washington, over 95 percent and changes in the velocity, turbulence, and of tidal wetlands have been lost (Gregory and pattern of freshwater discharge that fluctu­ Guillermo R. Giannico Bisson 1997). ates between water stagnation and flushing is on the faculty of the Department of Fish­ Dikes are elevated earthen embankments flows. In turn, these changes in the circula­ eries and Wildlife at raised along tidally influenced channels in tion of water between both sides of a dike Oregon State Univer­ estuaries and coastal sections of rivers to keep cause alterations in water temperatures, soil sity, and Jon A. Souder low-lying lands from being flooded during is executive director moisture content, sediment transport, and of the Coos Watershed high tides. Structures known as flood boxes, channel morphology (Vranken and Oenema Association. or tide boxes, are installed in dikes to control 1990; Charland 1998).

© 2004 by Oregon State University small “pet doors” (figure 5) (Char­ land 2001). Tide gates open and close because of water level differ­ ences between the downstream and the upstream sides of the gate. Water a level differences are caused by (1) tidal cycles (and magnitudes), (2) inflow into the reservoir pool that forms on the upland side, and (3) the extent to which this reservoir pool has been drained during previous gate-opening cycles. The amount of water level b difference required to open a tide gate is determined by the “effective weight” of the gate. For top-hinged gates, both the amount of time and the degree of opening are functions of the weight and area of the gate and the pressure force generated by the difference in water level between both sides of the gate (Raemy and Figure 1. Flood box (culvert with tide gate) installed in dike’s wall: (a) top view; Hager 1998). Thus, the difference (b) side view. in water level needed to open a gate is greater the larger the gate and the more it weighs (USACE 2001). The chemical effects of tide passage. Thus, the effect that flood Conversely, for side-hinged gates, gates consist of upstream increases in boxes have on the aquatic environ­ the effective weight of the gate is water nutrient concentration, tur­ ment depends on a combination of a function of the resistance of its bidity, and heavy metal suspension things: culvert diameter relative to hinges and the degree to which the and reductions in dissolved oxygen the upstream channel; culvert surface door is tilted downward. In general, and pH (that is, water alkalinity) roughness; channel bottom charac­ and because of the opening force (Portnoy 1987; Vranken and Oenema teristics both upstream and down­ caused by their tilt, side-hinged gates 1990). Soil salinity is also reduced stream from the flood box; culvert open wider and for longer periods because tide gates prevent brackish bottom (also known as invert or sill) with less upland water pressure than tidewaters from reaching past dikes, elevation relative to the channel equivalently sized top-hinged gates. and the freshwater that is allowed bottom and to tide levels; type of tide Top-hinged tide gates may have “pet to drain toward the estuary removes gate; wing wall orientation; presence doors” that are hinged at the top, salts from soils over time (Dreyer of pilings in the channel; and other side, or bottom. These smaller doors and Niering 1995). features of the flood box (figures 1a remain open for longer periods than The biological effects of tide and 1b). the large gates they are part of and, gates come in the form of obstruc­ There are many different types as a result, they facilitate fish passage tion to fish migration, changes to the of tide gates, but the traditional (Charland 2001). composition of aquatic plants, and configurations have either a heavy lid Unfortunately, tide gates can pulses of coliform bacteria into estu­ (made of treated wood) suspended easily be jammed by floating pieces arine waters during low tides (Eliasen from the top of the culvert by either of wood, and, over time, they tend to 1988; Charland 2001). a bar with hinges or chains (figure hang twisted from their hinges. This Although the tide gate itself is 3a), or a metal lid (usually of cast changes the way the gates operate what stops water and fish movement, iron or steel) double hinged from and creates problems in terms of it is important to recognize that the above (figure 3b). Alternative designs both fish passage and flood control. design of the entire flood box affects include side-hinged gates (figures Regular inspections are recommend­ the circulation of water and fish 4a–c) and top-hinged gates with ed to avoid this type of problem.

2 The Effects of Tide Gates in Estuarine Habitats and Migratory Fish Tide Flooding Tide Flooding

a b

Tide Ebbing Tide Ebbing

c d Figure 2. Side view of tide gate: (a) closing, as upstream water level drops and tide level (see arrow) begins to increase; (b) closed, as tidal water level gets higher (see arrow) than upstream freshwater level; (c) opening, as tidal water level becomes lower (see arrow) than the freshwater level inside culvert; (d) open, during low tide (see arrow) before upstream water level begins to decline.

Physical Effects Changes to Water Temperature is because water temperatures during Water temperature not only the spawning periods are below the of Tide Gates plays a critical role in affecting spawning temperature standard. Because tide gates cause freshwater Changes to Channel Morphology the speed at which many chemi­ cal processes occur (Richardson stagnation and restrict tidal inflow, Channel morphology is altered and Vepraskas 2001), but it is also they tend to increase upstream water by tide gates in two ways. First, up­ extremely important in determining temperatures. The increased peri­ stream scour tends to form an inlet the suitability of habitat for different od of water circulation allowed by pool, and the water jet through the aquatic organisms. Water tempera­ side-hinged gates may result in lower culvert forms a deep scour pool on ture criteria are established under water temperatures by reducing the outlet end. Second, if the flood the Clean Water Act for salmon and freshwater stagnation and augment­ box is replaced and the bottom of the trout spawning (55˚F) and nursery ing cooler estuarine inflow. culvert is set at a lower level, then (64˚F) habitats (ODEQ). In Oregon upstream erosion of the accumulated and Washington, limiting tempera­ sediments could result in changes to tures in coastal streams typically the channel morphology. affects summer nursery habitat. This

The Effects of Tide Gates in Estuarine Habitats and Migratory Fish 3 a

Figure 3. Top-hinged tide gates (a) suspended with chains, (b) held in place by metal arms, and (c) illustrated. b

Chemical Effects the amount of tidal exchange (that is, the difference between high and of Tide Gates low tides for any specific cycle) and by the amount of freshwater entering Changes to Water the estuary from tributary streams. Salinity In the Pacific Northwest, freshwater Salinity in wetland flow into estuaries varies by season, soils determines their with high flows during the winter oxidation-reduction and spring and low flows during the potential, ultimately summer and fall. Because salt water controlling soil pH. has a greater density than freshwater, Soil pH, in turn, affects it tends to occupy the lower portion the sequestration and of the water column. Thus, incoming liberation of heavy salt water dives below the outgoing metals. freshwater and creates a wedge that Water salinity moves along the bottom. The size in estuaries varies and shape of this wedge depend on daily and seasonally. the volume of freshwater that enters Daily variations are the estuary, the shape of the estuary, influenced by tides, and the prevailing coastal currents. as water with higher A tide gate prevents the flooding Tidal level salinity flows from the of upland channels by brackish water. mouth of the estuary inland during As a result, a dramatic difference in flood tide and back toward the ocean salinity exists between one side of during ebb tide. The extent of brack­ the gate and the other. When the ish water upstream is determined by gate opens, pooled freshwater moves c into the estuarine channel, creating a 4 The Effects of Tide Gates in Estuarine Habitats and Migratory Fish a b

Figure 4. (a) On the left is a side-hinged round gate and on the right, in the same photo, is a top-hinged gate with a mitigator fish-passage device; (b) a side- hinged rectangular gate; and (c) (right) diagram of an open side-hinged gate. Tidal level

c tongue of fresher water that, through common when culverts corrode or Changes to Heavy-Metal Concentration turbulence, mixes as it moves down crack upstream from the gate. In in Water the estuary. The speed of the salinity addition, leaks may happen when Soils in estuarine marshes are mixing—and the extent of the fresh­ salt water percolates through a dike’s naturally anaerobic (that is, they water tongue—is related to the type fill material because of the hydrau­ lack oxygen). When the operation and size of the gate, the amount of lic pressure caused by high tides. of tide gates begins to lower the freshwater pooled upstream, and the Whenever brackish water enters the salinity of soils on the upland side relative difference in salinity between upland side of a dike, it occupies the of dikes and periodically desiccate fresh and brackish water in the area bottom layer of water in upstream them, these soils become exposed (Jay and Kukulka 2003). pools. This water may form residual to air, and a variety of aerobic (that Over time, all tide gates begin to pools of brackish water if the fresh­ is, oxygen-driven) processes begin leak. Leaks occur if the seal between water outflow when a tide gate opens in them (Richardson and Vepraskas the gate and the supporting structure is insufficient to create the velocity 2001). If this occurs, immobilized, is uneven or if material is caught needed to mix both layers of water. when the gate closes. Leaks are also The Effects of Tide Gates in Estuarine Habitats and Migratory Fish 5 Tide Gates as Physical Barriers to Fish Passage Two factors influence the degree that a tide gate represents a physical barrier for fish. One is the length of time the gate is closed and the other, the size of the opening. Any tide gate represents a total barrier to fish passage during the time it remains completely closed. The length of this period depends on the magnitude of the tidal ex­ change (the difference between high and low tides), the water inflow into the upstream pool between opening cycles, and the degree to which this pool emptied during the previous cycle. Under normal conditions, Figure 5. A top-hinged gate with a small “pet door” attached to floater. top-hinged tide gates will not open until the water level inside the culvert reduced sulfides combined with the are tightly regulated, the impacts of is higher than the water level on the soil iron are oxidized and converted dikes and tide gates on migratory downstream side. These gates will into sulfates and sulfuric acid. These fishes have received relatively little close only when the water level on compounds make the soil acid (that attention. Only recently have the the downstream side is equal to or is, lower its pH) (Anisfeld and Benoit effects of dikes and tide gates on higher than the water level inside the 1997; Portnoy and Giblin 1997), salmon and trout movement and culvert. Because tidal cycles are ap­ and this acidification can cause the habitat access attracted the interest proximately 12 hours long and tides heavy metals in the soil (such as lead, of agencies and watershed councils as flood (flow in) about half of that time copper, silver, and cadmium) to be salmonids began to decline in abun­ and ebb (flow out) the other half, released into the water (Anisfeld and dance (Nehlsen et al. 1991). top-hinged tide gates are expected to Benoit 1997). In the particular case of anadro­ remain closed at least 50 percent of mous salmon and trout (which mi­ the time (that is, 6 hours within each grate from freshwater environments cycle, assuming the upstream pool Biological Effects to the sea and back), tide gates are empties completely during each cycle of Tide Gates alleged to negatively affect them, not and the gate closes by the combined only by preventing their migration effects of its own weight and slack Although tidal marshes pro­ but also by deteriorating the quality tide). However, depending on how vide critical habitat to many aquatic and connectivity of their habitats. they are installed and the characteris­ organisms (Healey 1982; Simens­ The notion that tide gates interfere tics of the area they drain, gates may tad et al. 1982; Shreffler et al. 1990 with fish migration has encouraged remained closed for longer periods. and 1992), store upland sediments the development of “fish-friendly” For example, Scalisi (2001) reported (Vranken and Oenema 1990; Port­ gate designs (Eliasen 1988; Thomson that during February 2001 the tide noy 1999), and regulate floodwaters and Associates 2000). Unfortunately, gate in Larson Slough, Coos Estuary, (Turner and Lewis 1997), the conse­ studies on the effectiveness of such Oregon, opened 4 hours after the quences of their alteration by diking alternative designs have not been beginning of ebb tides and closed at and filling has not attracted the same carried out by independent research slack tide, thus, representing a total attention from regulatory agencies institutions, and the limited informa­ barrier to fish passage 75 percent of as have other development projects. tion available on their effects comes the time. Whereas dams, roads, culverts, and entirely from tide gate manufactur­ Because all tide gates block fish water diversion projects have been ing companies. passage during all or most incom­ the focus of many impact studies, ing tides, there is no such thing and their construction or operations as a “fish-friendly” tide gate, only “fish-friendlier” ones. Compared 6 The Effects of Tide Gates in Estuarine Habitats and Migratory Fish to the most restrictive gates, a backwatering. layers of water is reached, turbulent “fish-friendlier” installation should Tide gates not only constitute di­ flow results. have a gate that opens wider and for rect physical barriers to fish passage, Turbulence and the associat­ longer periods of time, creates less but also create indirect obstacles to ed bubbling of air in water cause water velocity and turbulence, and fish in the form of elevated water vibration and noise that, depending provides a gradual transition between velocities and turbulence. Velocity on their magnitude, may represent fresh and salt water, with salinity criteria established for fish passage obstacles to fish movement. Heavy refugia available for juvenile fish. in culverts are similar to those used top-hinged tide gates produce a “Fish-friendlier” tide gate de­ for tide gates. In Oregon, the wa­ high-velocity jet of water, called vena signs employ three mechanisms to ter velocities recommended by the contracta (see figure 1b), which cre­ increase the physical passage period. Department of Fish and Wildlife are ates turbulence and bubbling (figure First, since gate weight determines 5 feet per second for adult salmonids 3b) (Pethick and Harrison 1981). the amount of water level difference in culverts 60 to 100 feet long, and This water jet is caused by the com­ required to open the gate and keep 2 feet per second for juvenile salmo­ bined effects of the upstream-down­ it open, the use of lighter materials nids (Robison et al. 1999). stream water level differences, the such as aluminum, fiberglass, and Average water velocities through tendency of the gate to close by the plastics in both top-hinged and side- tide gates are a function of two effect of its own weight (or restor­ hinged gates will increase the time things: (1) the upstream-downstream ative force), and the size of the gate. they remain open. water level difference, which to a On the basis of our observations, Second, because the “effective” degree varies through the tidal cycle turbulence seems to be lower with weight (that is, the gate-closing with different opening angles; and (2) “fish-friendlier” side-hinged gates force) of side-hinged gates is lower the width of the opening, which also (figure 4b) than with top-hinged than that of top-hinged gates, side- varies through the tidal cycle with ones. Because the forces that tend hinged gates will open earlier and different opening angles and which to keep the gate closed are lower in close later in a tidal cycle than top- is influenced by the resistance of the both side-hinged and light-weight hinged gates of equivalent size. Some gate to opening, depending on its tide gates, the jet of water and its side-hinged gates have been reported weight and design. Water velocities resulting water turbulence and bub­ to require only one inch of water through side-hinged gates are lower bling are practically eliminated. level difference to open up to 45˚ than through top-hinged gates of (Scalisi 2001). Such an opening angle similar size and weight because less Effects of Tide Gates with a small water level difference force is required to keep side-hinged on Salmon Nursery Habitats represents a significant improvement gates open. Also, lighter aluminum Estuaries play a critical role in to fish passage when the width of gates require less force to open, and juvenile salmonid survival during the the opening is factored in (one foot as a result, velocities through their transition from fresh to salt water is considered the minimum for adult openings are lower than with steel or (Pearcy 1992). Estuarine habitats fish passage by the Washington De­ cast-iron gates of comparable size. provide juvenile salmon with a pro­ partment of Fish and Wildlife). Water turbulence results from ductive feeding area, a refuge from A third mechanism employed the effects of shear forces caused by marine predators, and a transitional to improve gate fish passage was drag in water velocity at the edges of zone for gradual acclimation to salt designed by Leo Kuntz (personal channels, through obstructions, or water (Thorpe 1994). communication). This mechanism where differences in viscosity occur Because tide gates interfere with is a float-activated cam, known as a (Goldstein 1965). The width and the water flow in the boundary zone mitigator fish-passage device, that is shape of the channel, its substrate between estuaries and streams, they wedged between the gate and the composition, bank roughness, and negatively affect the coastal marsh mouth of the culvert to keep the protuberances in the channel all habitats of juvenile salmon. They gate open during incoming tides reduce the velocity of the layer of do this not only by altering water (see right tide gate in figure 4a). The water that is in contact with the walls quality and channel morphology, floats regulate the amount of back- of the channel (or culvert, in the case but also by changing the species of flow allowed upstream before the of a flood box) in relation to the av­ aquatic plants and invertebrates (for gate closes when the cam is released erage velocity of the rest of the water example, insects and crustaceans) by the upward movement of the column. When a critical threshold in that juvenile fish rely on for cover floats under a rising tide. The tidal the velocity difference between these and food. level at which the cam is released is adjustable to regulate upstream The Effects of Tide Gates in Estuarine Habitats and Migratory Fish 7 Gregory, S. V., and P. A. Bisson. 1997. Portnoy, J. W. 1999. Salt marsh diking Literature Cited Degradation and loss of anadromous and restoration: biogeochemical Anisfeld, S. C., and G. Benoit. 1997. salmonid habitat in the Pacific North­ implications of altered wetland hy­ Impacts of flow restriction on salt west. Pages 277–314 in D. J. Stouder, drology. Environmental Management marshes: an instance of acidification. P. A. Bisson, and R. J. Naiman, edi­ 24:111–120. Environmental Science & Technology tors. Pacific salmon and their ecosystems: Portnoy, J. W., C. T. Roman, and M. 31:1650–1657. status and future options. Chapman and A. Soukup. 1987. Hydrologic and Charland, J. W. 1998. Tide gate modifica­ Hall, New York, New York. chemical impacts of diking and tions for fish passage and water quality Healey, M. C. 1982. Juvenile Pacific drainage of a small estuary (Cape Cod enhancement. Tillamook Bay National salmon in estuaries: the life support National Seashore): effects on wildlife Estuary Project, Garibaldi, Oregon. system. Pages 315–41 in Victor S. and fisheries. Pages 254–65 in W. R. ______. 2001. Alternative tide gate Kennedy, editor. Estuarine comparisons: Whitman and W. H. Meredith, edi­ designs for habitat enhancement and proceedings of the sixth biennial inter­ tors. Waterfowl and wetlands symposium: water quality improvement. Marine En­ national estuarine research conference, proceedings of a symposium on waterfowl vironment Engineering Technology Gleneden Beach, Oregon, November 1–6, and wetland management in the coastal Symposium, Alexandria, Virginia. 1981. Academic Press, New York. zone of the Atlantic flyway. Delaware Dahl, T. E. 1990. Wetland losses in the Jay, D. A, and T. Kukulka. 2003. Revising Department of Natural Resources United States: 1780s to 1980s. U.S. the paradigm of tidal analysis—the and Environmental Control, Dover, Department of the Interior, Fish and uses of non-stationary data. Ocean Delaware. Wildlife Service, Washington, D.C. Dynamics 42:1–16. Portnoy, J. W., and A. E. Giblin. 1997. Daiber, F. C. 1986. Conservation of tidal Kuntz, Leo. Personal communication. Effects of historic tidal restrictions on marshes. Van Nostrand Reinhold, Nehalem Marine, 24755 Miami River salt marsh sediment chemistry. Biogeo­ New York, New York. Road, Nehalem, Oregon 97131. chemistry 36:275–303. Doody, J. P. 2001. Coastal conservation and Middleton, B. 1999. Wetland restoration, Raemy, F., and W. H. Hager. 1998. management: an ecological perspective. flood pulsing, and distribution dynamics. Hydraulic level control by hinged Kluwer Academic Publishers, Boston, John Wiley & Sons, New York, New flap gate.Proceedings Insitute of Civil Massachusetts. York. Engineers, Water, Maritime, and Energy 130:95–103. Dreyer, G. S., and W. A. Niering. 1995. Nehlsen, W., J. E. Williams, and J. A. Tidal marshes of Long Island Sound: Lichatowich. 1991. Pacific salmon Richardson, J. L., and M. J. Vepraskas ecology, history and restoration. Con­ at the crossroads: stocks at risk from (editors). 2001. Wetland soils: genesis, necticut College Arboretum Bulletin, California, Oregon, Idaho, and Wash­ hydrology, landscapes, and classification. Connecticut College Arboretum, ington. Fisheries 16(2):4–21. CRC Press, Boca Raton, Florida. New London, Connecticut 34:1–72. NRC (National Research Council). 1996. Robison, E. G., A. Mirati, and M. Allen. Eliasen, R. 1988. Side hinged flap gates: Upstream: salmon and society in the 1999. Oregon road/stream crossing res­ an alternative to salmonid migration Pacific Northwest. National Academy toration guide: spring 1999. Advanced barriers in flood drainage. Department Press, Washington, D.C. fish passage training version. Ore­ of Fisheries and Oceans, Nanaimo, ODEQ (Oregon Department of En­ gon Department of Forestry, Salem, British Columbia. vironmental Quality). Chapter 340. Oregon. Frenkel, R. E., and Morlan, J. C. 1991. Water pollution. Division 41. State­ Scalisi, M. 2001. Larson Slough tidegate Can we restore our saltmarshes? wide water quality management plan; study: an investigation of the hydro­ Lessons from the Salmon River, Ore­ beneficial uses, policies, standards, and dynamics across the Larson Slough gon. Northwest Environmental Journal treatment criteria for Oregon. http:// Inlet and water quality of Larson 7:119–135. www.epa.gov/ost/standards/wqsli­ Slough. Second Draft Report to the Coos Watershed Association. Goldstein, S. (editor). 1965. Modern brary/or/or_10_wqs.pdf developments in fluid dynamics: an Pearcy, W. G. 1992. Ocean ecology of North Schultz, S. T. 1990. The Northwest coast: a account of theory and experiment relating Pacific salmonids. University of Wash­ natural history. Timber Press, Port­ to boundary layers, turbulent motion and ington Press, Seattle. land, Oregon. wakes. Vol. I. Dover, New York, New Pethick, R. W., and A. J. M. Harrison. Shreffler, D. K., C. A. Simenstad, and R. York. 1981. The theoretical treatment of the M. Thom. 1992. Foraging by juvenile hydraulics of rectangular flap gates. salmon in a restored estuarine wet­ Pages 247–254 in Proceedings, 19th land. Estuaries 15:204–213. congress, International Association for Hydraulic Research, New Delhi, India 1–7 February 1981.

8 The Effects of Tide Gates in Estuarine Habitats and Migratory Fish Shreffler, D. K., C. A. Simentstad, Thorpe, J. E. 1994. Salmonid fishes and and R. M. Thom. 1990. Temporary the estuarine environment. Estuaries residence by juvenile salmon in a 17:76–93. restored estuarine wetland. Canadian Turner, R. E., and R. R. Lewis. 1997. Journal of Fisheries and Aquatic Sciences Hydrologic restoration of coastal wet­ 47:2079–2084. lands. Wetlands Ecology and Manage­ Simenstad, C. A., K. L. Fresh, and E. O. ment. Special issue: Hydrologic resto­ Salo. 1982. The role of Puget Sound ration of coastal wetlands 4:65–72. and Washington coastal estuaries USACE (U.S. Army Corps of Engi­ in the life history of Pacific salmon: neers). 2001. HEC-RAS river analysis an unappreciated function. Pages system—hydraulic reference manual. 343–364 in V. S. Kennedy, editor. Version 3.0. U.S. Army Corps of Engi­ Estuarine comparisons. Academic Press, neers, Institute for Water Resources, New York, New York. Hydrologic Engineering Center, UC Thomson, A. R., and Associates. 2000. Davis, California. Flood boxes as fish migration barriers in Vranken, M., and O. Oenema. 1990. lower mainland streams. Prepared for Effects of tide range alterations on the Ministry of Environment, Lands salt marsh sediments in the Eastern and Parks, Region 2, Vancouver, B.C. Scheldt, S. W. Netherlands. Hydrobio­ logia 195:13–20.

The Effects of Tide Gates in Estuarine Habitats and Migratory Fish 9

This research and publication were funded by the National Sea Grant College Program of the U.S. Department of Commerce’s National Oceanic and Atmospheric Administration, under NOAA grant number NA76RG0476 (project number R/HBT-07-PD), and by appropriations made by the Oregon State legislature. The views expressed herein do not necessarily reflect the views of any of those organizations. Sea Grant is a unique partnership with public and private sectors, combining research, education, and technology transfer for public service. This national network of universities meets the changing environmental and economic needs of people in our coastal, ocean, and Great Lakes regions.

Credits Editing and layout: Sandy Ridlington Illustrations: Jon A. Souder Photographs: Coos Watershed Association

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