Briefing Book - Glossary. Accretion due to stream sediment added naturally to the shore Puget Sound, Everett

Transcription

1 Glossary

2 Accretion: Accretion is the process of adding sediments to a beach, whether naturally (material deposited by water or blown in by the wind) or artificially (material placed by humans). Accretion adds to the beach elevation and beach width. Accretion due to stream sediment added naturally to the shore Puget Sound, Everett Accretion due to construction of a partial barrier to natural sediment transport Puget Sound, Normandy Park Backshore: The backshore is the upper area of a beach above the reach of normal waves and tides, landward of the beach face. The backshore is subject to periodic flooding by storms and higher than normal tides. Backshore with drift logs and vegetation Puget Sound, Hood Canal Schematic of nearshore area and beach features, including backshore 2

3 Bathymetry: Bathymetry is the measurement of the bottom depth at various places in a body of water. In Elliott Bay, water depths range from 2m (red) to 180m (purple). At right is a color shaded-relief bathymetry map of the Duwamish Delta in Elliott Bay. The colors show relative depths with reds representing shallow regions and blues representing deeper regions. Red Orange Yellow Green Purple 2 meters 25 meters (approximate) 50 meters (approximate) 100 meters 180 meters Elliott Bay bathymetry (National Seafloor Mapping and Benthic Habitat Studies - Color shaded relief map of Duwamish Delta; USGS 2001) Beach: A beach is the zone of unconsolidated material that extends landward from the low water line to a site-specific place where there is a marked change in material form such as a bluff, escarpment, or a line of permanent vegetation. Typically, intertidal beaches in Puget Sound are composed of mixed sand and gravel. Puget Sound, Bainbridge Island 3

4 Beach Berm: A beach berm is a nearly horizontal portion of the beach or backshore formed by deposition of sand or gravel by wave action, typically forming above high water. Multiple berms may be present. beach scarp beach berm beach face Beach Fill (Beach Nourishment): Beach fill is the artificial placement of sediments, such as sand, gravel, and cobble, to elevate and extend the shoreline seaward of its existing location. Beach nourishment (also referred to as beach replenishment) is the process by which shoreline-eroded sediment is replaced on a beach. Natural nourishment involves the transport by waves and currents of the nourishment material from a source of material, typically an eroding bluff, to the affected area. A beach nourishment project is a beach fill project designed to certain wave and littoral current parameters so that the beach remains viable for a design life or given period of time. Beach nourishment may be designed as a coastal protection mechanism. Beach nourishment construction After construction Puget Sound, Mukilteo (Mukilteo beach) 4

5 Beach Scarp: A beach scarp is a nearly vertical slope along the beach caused by wave action eroding the beach and is formed over a short period of time. A beach scarp may vary in height depending on the waves and the characteristics of the beach sediment. Puget Sound, Whidbey Island Breaking Wave: A breaking wave is a wave that has increased to its maximum height in shallow water, thereby becoming unstable and tumbling forward, dissipating its energy. Wave breaking is a complex process dependent on many factors such as local wave height, wave period, water depth, and beach slope. Puget Sound, Edmonds waterfront 5

6 Breakwater: A breakwater is an engineered structure built in the nearshore zone to protect harbors, marinas, beaches, and upland property from wave damage. A breakwater can be made of several types of materials, including stone, timber, and sheet piles. Rock breakwater protecting Shilshole marina Puget Sound, Seattle waterfront Bulkhead: A bulkhead is a structure designed to retain or prevent sliding of the land. A secondary purpose is to protect the upland against damage from wave action. Dockton Road shoreline Puget Sound, Vashon Island 6

7 Coastal Erosion: Coastal erosion is the removal of land materials at the coast by forces of water and wind. Unconsolidated, small-size sediment, such as sand, is most susceptible to coastal erosion. Wave attack and channelized flow are the main agents of erosion. Groundwater pressure in steep slopes can also aid erosion. Chronic erosion is sediment erosion persisting for a long period of time. Episodic erosion is sediment loss that occurs only occasionally. Episodic erosion (result of January 2007 storm) Puget Sound, Burien shoreline Chronic erosion (west side of Whidbey Island) Puget Sound, Whidbey Island Deck Light or Prism: A deck light or prism is a light source inserted into the deck of a pier or wharf to provide light below. 7

8 Dredging: Dredging is the removal or displacement of sand, silt, gravel, or other submerged materials from the bottom of water bodies, riparian watercourses, or natural wetlands. Dredging is done to maintain channel depths for navigational purposes and for cleanup of polluted sediments. Shoreline dredging operation Eelgrass and Eelgrass Beds: Eelgrass is a species of sea grass that occurs along the coast of the Pacific Northwest. Eelgrass can form small patches to large meadows in the low intertidal and shallow subtidal zone in Puget Sound. Established eelgrass beds provide shelter for snails, crabs, shrimp, starfish, sea anemones, sea cucumbers, brittle stars, sea squirts, and many other marine creatures. Eelgrass (Zostera marina) 8

9 Ekki Wood: Ekki wood is a dense hardwood from Africa. Because Ekki wood is normally impervious to marine borers, it has been used on the Elliott Bay seawall to replace corroded steel sheet face panels. Unfortunately, Ekki wood is not as impervious as once thought. In places along the seawall, the Ekki wood panels are infested by the same organisms that have penetrated the seawall s timber supporting structures. Ekki wood panels along the Elliott Bay seawall Estuary: Estuaries are bodies of water along the coast that are formed when fresh water from rivers flows into and mixes with saltwater from the ocean. This mixing of fresh and saltwater creates a unique environment that supports a variety of organisms. Niawiakum River, Willapa Bay, Washington Source: Washington State Department of Ecology 9

10 GARDENS Horizontal Gardens: Horizontal gardens are plantings of live kelp or eelgrass situated water ward of a seawall. Horizontal gardens have the potential to provide shelter for snails, crabs, shrimp, starfish, sea anemones, sea cucumbers, brittle stars, sea squirts, and many other marine creatures, thus improving the diversity of nearshore organisms. In areas where live plants are not feasible, artificial vegetation could serve as shelter for migrating salmonids and substrate for algae and other marine organisms. Giant kelp could be used for horizontal gardens Vertical Gardens: Vertical gardens or living walls are plantings of live plants along a wall and are common in small urban spaces. Using the vertical garden concept, aquatic plants could be installed on the face of a seawall. Attaching plants on a frame along a seawall can provide substrate for other organisms and hiding places for salmonids. Habitat enhancing marine structures for urban waters. From a presentation given by Karen Dyson to Seattle Public Utilities on November 3,

11 Glass Blocks: The use of glass blocks over deck grating is one technique for enhancing light levels under a pier, walkway, dock, or wharf. Glass blocks were installed at the Clinton Ferry Terminal pedestrian walkway to improve light levels for eelgrass beds below the structure. Clinton Ferry Terminal s pedestrian walkway Whidbey Island, Puget Sound Groin: A groin is a shore protection structure built (usually perpendicular to the shoreline) to trap littoral drift material or reduce erosion of the shore. GROIN Puget Sound, Normandy Park 11

12 Habitat Enhancements: Habitat enhancements refer to engineered structures incorporated into the design of a seawall to improve environmental conditions of nearshore habitat. See habitat skirt (Vancouver, BC) and intertidal bench (Olympic Sculpture Park) for examples of habitat enhancements designed to provide texture and structure to a vertical wall for the colonization of a succession of aquatic organisms. Habitat Skirt: A habitat skirt or apron is an artificial reef designed to create new marine intertidal habitat. As part of the Vancouver Convention Center expansion, the City of Vancouver, BC installed a habitat skirt. Resembling long stadium bleachers, the skirt provides connectivity with existing shorelines for migrating juvenile salmon and other fish species. Habitat skirt Vancouver, BC 12

13 High Tide: High tide is when water meets land at its deepest, with the least amount of beach exposed. Low tide is when the water is the shallowest at that location, with the most beach exposed. Puget Sound tides move in daily, monthly, and yearly cycles. There are two high and two low tides every day, caused by combined effects of the gravitational forces of the moon and sun on the earth s rotation. The levels of the first and second high tides are rarely the same in a given 24-hour cycle. Similarly, the levels of the first and second low tides are rarely the same. Examples of high and low tide Puget Sound, Edmonds waterfront 13

14 Intertidal (Habitat) Bench: An intertidal (habitat) bench is an engineered structure installed at the base of a seawall to form a shallow angle to the seafloor and provide shallow water structure for the establishment of aquatic vegetation. An intertidal bench was built along the full length of the Olympic Sculpture Park shoreline, in the lower intertidal zone, to improve the salmon migratory route through the area. Currently, algal growth and invertebrate presence is being monitored on the habitat bench. Salmon food sources have been found along the bench. Habitat bench Puget Sound, Seattle (Olympic Sculpture Park) 14

15 Intertidal Zone (Foreshore, Littoral Zone): Also known as the foreshore and littoral zone, the intertidal zone is the area exposed to the air at low tide and under water at high tide (for example, the area between tide marks). This area can include many different types of habitats, including steep rock cliffs, sandy beaches, or wetlands. Organisms in the intertidal zone are adapted to an environment of harsh extremes of temperature change and water availability. The intertidal zone along Puget Sound provides food and serves as a migratory route for endangered salmonids and other fish species. 15

16 Lagoon: A lagoon is a shallow body of water, such as a pond or lake, isolated by a barrier beach or other narrow body of land. Lagoons do not have a freshwater source and may or may not have a permanent tidal connection to the sea. Lagoon at Lake Hancock Whidbey Island, Puget Sound Light Enhancements: In aquatic habitats, light levels affect water temperature, biological processes, and plant growth. Altered light levels, such as increased shading from overwater structures, piers, and protective structures, can negatively affect these parameters. Distributions of invertebrates, fish, and plants have been found to be severely limited in under-dock environments when compared to adjacent vegetated habitat not shaded by overwater structures.* In addition, lights from shoreline development may influence salmonid use of nearshore and migration patterns. Several habitat light enhancing options are being investigated in Washington state. These include grating, glass blocks, and deck prisms around the edges of a dock or overwater structure to create a transition area helping fish to adapt to the light/dark boundary. *2007, King County King County Shoreline Master Program. Appendix E: Technical Appendix. 16

17 Light Permeable Deck Grating: Light permeable deck grating is overwater grating that is designed to allow light to travel under a structure. Clinton Ferry Terminal Whidbey Island, Puget Sound Littoral Drift (Nearshore Drift, Longshore Drift): Littoral or longshore drift is the movement of sediments or sands along a coast parallel to the shoreline. Longshore drift arises when waves approach the shore obliquely. Waves striking the shore at an angle, as opposed to straight on, cause the water that washes up to the shore (wave swash) to move up the beach at an angle. The swash moves sediment particles up the beach. The backwash or seaward current brings sediment particles away from the beach. This has the net effect of a slow movement of the particles along the shore. A net movement of water also occurs, establishing a longshore current. Longshore drift is one of the principal processes in the overall sustainability of beach deposits. Longshore currents and longshore drift are generally considered to be constructive processes. 17

18 Longshore Current: Longshore current is water flowing essentially parallel to the shoreline in the nearshore zone. A longshore current is usually generated by waves breaking at an angle to the shoreline but also can be generated by a tidal current. (See image for Littoral Drift) Low Tide: Low tide is when the water is the shallowest at a location and exposes the most beach. Examples of high and low tide Puget Sound, Edmonds waterfront 18

19 Mean High Water (MHW): Mean high water is the average level of all high waters (high tide) at a place over a 19-year period as established by the National Oceanic and Atmospheric Administration. Mean Higher High Water (MHHW): Mean higher high water is equal to the average of the higher of the two daily high tides over a 19-year period as established by the National Oceanic and Atmospheric Administration. Mean Low Water (MLW): Mean low water is the average level of low water at a place over a 19-year period as established by the National Oceanic and Atmospheric Administration. Mean Lower Low Water (MLLW): Mean lower low water is equal to the average of the lower of the two low tides each day over a 19-year period as established by the National Oceanic and Atmospheric Administration. Nearshore: The nearshore is the area where the interplay of various physical processes creates and maintains shoreline features and habitats. The nearshore environment covers the most productive waters of Puget Sound and encompasses a wide range of habitat types, from marshes and sand flats to kelp and eelgrass beds and upland areas. The nearshore extends down to the depth where light can no longer support photosynthetic plants on the bottom. Nearshore Drift: (See Littoral Drift) 19

20 Photic Zone: The photic zone is the surface layer of the ocean that is penetrated by sunlight. In the photic zone phytoplankton (microscopic free floating aquatic plants such as algae) flourish; this zone is where familiar fish, marine mammals, and marine invertebrates are found. Light can penetrate down to approximately 100 meters or 330 feet, which marks the end of the photic zone. Light can penetrate down to approximately 100 meters or 330 feet which marks the end of the photic zone Pier: A pier is a structure, usually of open construction supported by piling, extending into the water from the shore to serve as a landing place for vessels and for transferring material between a vessel and shore. Pier 59 Puget Sound, Seattle waterfront 20

21 Piling: A piling is a group of piles driven vertically or nearly vertically into the bottom of a bay or harbor to support a dock, pier, or equipment or to aid in maneuvering vessels. Piles are made of timber, steel, reinforced concrete, and other materials. Concrete piles supporting Pier 91 Puget Sound, Seattle waterfront Pocket Beach: A pocket beach is usually a small beach between two headlands. In an ideal setting, there is very little or no exchange of sediment between a pocket beach and the adjacent shorelines. The Olympic Sculpture Park created a pocket beach where rip rap had once been. The newly created habitat provides a gentle sloping shoreline. The pocket beach includes plantings of native riparian vegetation that connect the land to the water. Pocket Beach Headlands Area before construction Olympic Sculpture Park pocket beach looking south Puget Sound, Seattle waterfront 21

22 Pocket Estuary: A pocket estuary is a term used in the Puget Sound region to describe small estuaries and lagoons that are connected with the Sound but are partially isolated by their configuration from the main body of Puget Sound. Pt. Monroe Puget Sound, Bainbridge Island Propeller Wash: Propeller wash is a high-velocity jet of water generated by a ship s propeller that is capable of eroding bottom sediments far from the propeller. 22

23 Revetment: A revetment is a facing of stone, concrete, or other materials built to protect an embankment, shore face, or shore structure against erosion by wave action or currents. Puget Sound, Kingston Riparian Areas: Riparian areas are lands adjacent to lakes, streams, marine shorelines, wetlands, and other aquatic systems. Marine riparian areas protect water quality by filtering or absorbing contaminants, provide shade that keeps water temperature low, provide wildlife habitat and food for fish, and provide soil stability and sediment control. Riparian areas also provide nearshore habitat structural elements, such as large woody debris, that provide shelter for many land and aquatic organisms and are a source of sediments that help sustain beaches. Typical Washington coastal riparian areas 23

24 Rip Rap: Rip rap is a layer, facing, or protective mound of stone placed in water to prevent erosion, scour, or sloughing of a structure or embankment. Rip rap is used for revetment, toe protection for bluffs, or structures exposed to wave action. Rip rap along the Elliott Bay seawall Puget Sound, Seattle waterfront Salmon Migratory Route: A salmon migratory route is a route juvenile salmon take along the shoreline in their migration from rivers/streams out to marine waters. Salmon migratory routes typically occur near the shoreline and in shallow waters (depending on species). Adult salmon return from marine waters to their native river along a migratory route but are less shoreline oriented. The nearshore area along the Elliott Bay seawall is the migratory route for several salmonid species including Chinook salmon. Seawall: A seawall is a structure built along a portion of a coast primarily to prevent erosion and other damage by wave action. Seawalls retain earth against a shore face. Elliott Bay seawall Puget Sound, Seattle waterfront 24

25 Seawall Habitat Panels: Seawall habitat panels are concrete panels of various shapes and sizes that were installed on the Elliott Bay seawall in 2008 to test whether adding structure and texture to a vertical seawall can increase biodiversity. The University of Washington has been monitoring the panels since their installation. The monitoring has indicated a succession of colonizing organisms including algae, mobile invertebrates, and barnacles. Monitoring will continue through Habitat test panels Puget Sound, Seattle waterfront Sediment: Sediment is unconsolidated loose fragments of rocks, minerals, or organic material (such as shells) generally transported from their source by water, wind, or ice and deposited elsewhere (such as downstream). Typical sediment found in Puget Sound 25

26 Sheet Pile: A sheet pile is an individual long, thin structural member that is driven vertically into the ground, generally forming the structure of a wall. Each sheet pile interlocks with adjacent sheet piles to form a rigid sheet pile wall and retain an embankment or fill structure. A sheet pile is fabricated from steel, concrete, or other materials, such as plastic or fiberglass. Sheet piles (left) and sheet pile wall at Pier 48 (right) Puget Sound, Seattle waterfront Shore: The shore is the strip of ground bordering any body of water that is alternately exposed or covered by tides and/or waves. Bush Point Puget Sound, Whidbey Island 26

27 Shoreline: The shoreline is the line of contact between the land and a body of water. On National Oceanic and Atmospheric Administration nautical charts and surveys, the shoreline approximates the mean high water line. 27

28 SOIL STABILIZATION METHODS Soil stabilization is a construction technique for improving soils that are easily erodible or liquefiable. Several soil stabilization methods are being discussed for construction of the Elliott Bay seawall. Two examples include drilled shafts and jet grouting. Both techniques would occur behind the existing seawall face. Drilled Shaft: Drilled shafts are created by driving piles behind an existing seawall structure. Drilled shafts are also called secant piles. Drilled shafts protect a waterfront from erosive forces and are designed consistent with current seismic codes. There are multiple options for configuring a drilled shaft structure. A number of seawall face treatments can be added to this or any structure to determine the final look and feel of a seawall. Facing Sidewalk Viaduct shown removed Alaskan Way Existing timber platform Soil anchors Viaduct shown removed Existing seawall panel Drilled Shaft Sidewalk Alaskan Way Drilled shaft example Facing Existing timber platform Jet Grouting: Jet grouting is a ground improvement technique that stabilizes a specific area of soil through the injection of a cement slurry. There are multiple options for configuring a ground improvement injection structure. Jet grouting provides Existing a similar level of tidal and seawall panel seismic protection as a drilled shaft method. A number of face treatments can also be Drilled Shaft added to a jet grouting structure. Existing face of seawall Sidewalk Viaduct shown removed Alaskan Way Existing face of seawall Sidewalk Viaduct shown removed Alaskan Way Existing face panel to remain Existing face panel to remain Facing Facing Existing master pile wall Soil-cement block Soil anchors Existing master pile wall Soil-cement block Jet grouting example 28

29 Stepped Seawall Design: Stepped seawalls are a type of seawall designed to enable waves to break, dissipate wave energy, and repel the wave back to the sea preventing overtopping of the wall. Steps can be a way to provide access to the shore during low tides or when wave conditions are suitable. The White Bay seawall in Sydney, Australia was reconstructed with a stepped design of roughed-cut sandstone. The horizontal steps are a common feature, and the stone is of similar composition to local natural rocky shores. Stepped seawall Wheelers Bay, Isle of White Stepped design White Bay Seawall, Sydney, Australia Subtidal Zone: The subtidal zone is the area below the intertidal zone that remains submerged at low tide. This area is exposed briefly during extreme low tides around full and new moon events and provides habitat to a large diversity of plants and animals. 29

30 Tide Pools: Natural tide pools are intertidal areas housing plants and animals adapted to daily changes in temperature, moisture, oxygen, food sources, and predation. They form where pools of water collect in rocky hollows at low tide. Incorporation of tide pools into seawall design to enhance nearshore habitat is being examined in Australia. A large tide pool was created along the Spit Bay seawall and was designed to flood at high tide and provide a shallow water habitat at low tide. At another seawall in Australia, shallow tide pools were developed by leaving portions of the seawall structure open. Spit Bay, Sydney, Australia Shallow tide pools (Rock Pools) McMahon s Point, Sydney, Australia 30

31 Touch Point - Shoreline Public Access: Shoreline public access refers to the ability of the general public to reach, touch, and enjoy the water s edge. A water touch point is an area along the shoreline where the general public can touch the water. Example of a water touch point Sydney, Australia (Glebe Point Park) Wave Overtopping: Wave overtopping is water carried over the top of a coastal structure, due to wave run-up or surge action, exceeding the crest height of the structure. Wave overtopping is reported as a volumetric rate per unit distance, such as cubic feet/ second/foot, along an overtopped structure. Puget Sound, West Seattle shoreline 31

32 Wave Reflection: Wave reflection is the re-direction of a wave after impacting a steeply sloping structure, such as a revetment or bulkhead. SR 520 bridge, Lake Washington Wave Run-Up: Wave run-up is the height of wave uprush on a beach or structure measured vertically above the still water level of the water s surface. Puget Sound, West Seattle shoreline 32

33 Wharf (Wharves): A wharf is a type of pier that is constructed almost parallel to the shore and is sometimes referred to as a marginal wharf. Wharves can be used to moor vessels, support a building, or other operations. Strictly speaking, there are no wharves along the Seattle Central Waterfront, with the possible exception of Pier 66. Other than Pier 66, the nearest wharf is Port of Seattle Pier 46, which is also referred to as a container wharf or marginal wharf. Examples of wharves 33

34 August 2010