Week 11 - Physical Restoration (Dikes, Jetties, Training Structure, Pilings, Pile Dikes - Flashcards
Estuary Habitats
- Emergent salt marshes (high, low)
- Mud flats
- Eelgrass beds
Estuary Gradients
- Fluvial Gradient – Surface Flow and Sub-Surface “Hyporheic” Zone
- Tidal Gradient - Planform View and Lateral Connection
- Salinity Gradient
- Light Penetration
Fluvial Gradient
Surface Flow - relative to ocean energy influences estuary form, habitats, salinity, biota
Sub-Surface “Hyporheic” Zone - sub-surface exchange of fresh + saltwater, ions, nutrients. microbial activity. redox react.
Tidal Gradient
Planform View - tidal height (flux), influences the horizontal extent of the tidal zone, the extent of estuary
Lateral Connection- connectivity at low tide
Salinity Gradient
Salinity is affected by river discharge, tidal flux, winds, shoreline revetment, substrate, delta bathymetry, evaporation, and more
Determines what plant species can establish and where
Influences the distribution of organisms
Light Penetration Gradient
Photic Zone - Photosynthetic zone
Influenced by turbidity, sediment load of the river, water depth.
Affected by structures, log booms, piles
Influences phytoplankton, extent of submerged plant community
Ways to restore tidal, fluvial, salinity, photic gradients, leading to restored habitat structure
- Dikes/Jetties/Training Structures
- Pilings/Pile Dikes
- Flap Gates
- LWD
Pile Dikes
- Wood, Metal, Concrete
- Many uses!
- Bank training, control flow, and sediment movement contains dredge spoil
Pile Fields
support overwater structures like docks and moorages
tether log rafts
build residential, commercial, and industrial structures
Training Dikes
Primary purpose is to protect dredged material from eroding back into the navigation channel
oriented parallel to the river
typically linear and in some cases have short perpendicular wings to deflect flows and distribute energy.
Spur Dikes
Constructed perpendicular to the mainstem channel
Functionally reduces channel width to increase depth (and velocity) of the river thalweg
Transverse Dikes
Linear pile structures that cross an embayment or side channel
frequently associated with a spur or training dike and dredge material placement
in some cases, shallow water and marsh habitats form due to the construction of the dike and placement of dredge material.
Pile/Dike Stressors
- Interferes with sediment deposition and erosion processes
- Reduces flow circulation through shallow-water habitats, side-channels, and peripheral bays
- Reduces connection to refuge habitats
- Release of toxic contaminants into the water and sediments where pile structures are treated with preservatives (creosote)
- Pilings favor predators of salmonids, such as northern pike minnow, smallmouth bass, double-crested cormorants
- Possible habitat benefits? Restoration tool vs stressor?
What are some negatives and positives of pile structures?
Positives:
May trap available woody debris,
As untreated pilings decay, they may contribute macro detritus directly to the system
Plants hanging over the river may contribute litter and also insect prey
Reduce flow energy and provide “velocity shadows”, shallow refuge habitats
Negatives:
Cormorants use pilings, pile dikes, navigation aids and other structures as perches/resting
Creosote associated with industries that use toxic materials (eg, cannery sites – metal concentrations)
depositional environments - may trap and hold toxic-laden sediments, and assimilate toxins into the pile structures themselves
What are some methods to improve pile structures and are they acceptable?
Copper napthenate - a newer biocide to replace creosote is also a concern
Impairs juvenile salmonid olfactory function, affects salmonid growth and development, immune function, reproduction, predator avoidance, and much more
Removing treated piles may cause a pulse of contaminants to enter the system - test sediments, capp sediments, or remove them too
Replace piles with concrete, fiberglass composite, or steel pilings
