Midterm 2. Flashcards
Why are terrain maps important?
Terrain and stream stability are a key focus of the mapping. understand which areas are prone to flooding, mass land movements.
What is a Terrain map?
Descriptive data on the physical characteristics of the land surface.
- topography
- aspect
- landforms
- material properties
1st step in watershed terrain analysis
Determine what info is available.
Terrain maps, forest cover maps w/Sensitive areas
-Slope stability, geology maps, air photos
What are some general info aspects of Watershed assessment?
- Landforms and slope
- surficial materials
- geological processes
- BEdrock
- Hydrological characteristics
- Vegetation
Where can you find map info?
Terrain Info BCMoE
Federal Gov
BC Gov Sales Offices
What are possible problems with maps? Air photos
Inappropriate scale (Inability to differentiate small units)
- Area of delineated polygon not field checked
- Level of map usefulness- who mapped it.
Describe Basal till
- Rock fragments of various sizes and shapes in a matrix of predominantly silt clay
- Non-Stratified
- high compaction. variable minerology/texture
- depends of source materials moved by ice
Describe Ablation materials?
Later stages of glaciation (melting) non compact-coarse, sandy textures. relatively pervious materials -fine materials are washed away -hummocky landform
Fluvial sediments
Active braided channels flood plain fluvial fans non sorted-non bedded rapid aggradation
Glacial Fluvial deposits
Eskers, Kames terraces, outwash points, wide range of particle size,
Deltaic Deposits
Gravels and sand deposits
Lacustrine
Fine sediments settled from suspension in standing fresh water (lake)
-well sorted and stratified materials along beaches
varves- shows seasonal layers when in sediment horizon
littoral sediments
transported and deposited by wave action
varves
Seasonal layers when you cut into the lake sediment horizon
Glaciolacustrine materials
Deposited in or along the margins of glacial (ice dammed lakes) layers of silt and fine sand. kamloops
Marine Deposits
Marine mud mixtures
sediments deposited in salt or brackish water; clay silts and sands to well sorted and stratified modern beach
Large valleys at elevations of up to 250m (Kitimat valley, south coast fraser valley)
-shells
Glacial Marine
mud, silt, clay, shells
Colluvium
Materials that have reached thier present position as a result of direct gravity-induced movement
What are the 3 groups of colluvium?
- (rock slide) Talus slopes, colluvial mantles, rockslides, snow avalanche deposits ( loose angular rock fragments , non-cohesive , well drained)
- Debris flow and mudflow deposits (interlayer debris flow deposits-fluvial deposists
- earthflow and slumps, texture depends on source material (weathered bedrock, till) high clay content.
What materials make up colluvium
Range of size in poor-well stratified
boulders to rocks, pebbles to clay/
like a rock avalanche
Eolian deposits
Material transported and deposited by wind
- revegetated sand dune
- medium fine sand
- coarse silt that is well sorted
- non compacted
rock and bedrock
Soft volcanic rock weathered to clay
what are the two types of weathering
Chemical and physical
Volcanic Sediments
Ash, cinder lapilli volcanic bombs, tephra (flying magma turned to solid) basalt lava flow
Organic sediments
Organice material resulting from the accumulation of vegetative matter; thick level peat bog
-swampy areas
Define surficial materials
Non-litified unconsolidated sediments
how are surficial materials produced?
Weathering, sediment deposition, biological accumulation, volcanic activity and human activity
How are surficial materials classified?
Mode of origin: eroded and deposited by glacial ice; post glacial erosion by wind water and landslides; or accumulation of biological origin
What are Schematic Cross sections?
rough depictions of where between two points would we find different surficial materials and how large those sedposits may be
Alluvial Fans
Occur when confined channel enters a broad valley
-sediment deposition causes the channel to swing back n forth, developing a fan like shape`
Types of Alluvial fans?
- flood fans (low gradient channels)
- debris flow fans (steep with landslide deposits
What is FCN?
Natural Fan Channel Networks
What are 2 measures of FCN?
Channel extent (% of the fan surface covered by active channel) -Channel network complexity (# of channel nodes, where channels fork/join
Gullies
Steep, incised headwater channels
-sediment and woody debris onto lower valley slopes or into valley bottom streams
GAP intends to..
Identify the main factors affecting forest management in and around gullies
GAP provides..
a framework for managin gully systems before and after harvest
what are the 3 parts of GAP?
- Collection of field and air photo/map data
- Assess hazards and resources at risk
- Selection of management strategies and goals
Why gully assessment?
major part of riparian/stream network
high frequency of landslides, operationally difficult
hazardous for forestry work, public, water quality, fisheries
gully system hazards:
debris slides and flows
Water floods
fan destabilization
What does gully hazard level depend on?
climate and gully systems -size of catchment area # of triburary channels - slope angels on head wall and side wall -type of materials -channel and fan gradient -other woody debris and sediments
What are the components of GAP?
reach by reach assessment
reach by reach management strategies
What are the 7 GAP form components?
- Gully system Id
- Downstream Impact Potential
- Upslope debris flow potential
- Water transport potential
- Fan destabilization potential
- Debris flow initiation potential
- Post-logging conditions
What is downstream impact potential
Assessing the potential downstream impacts of all reaches in the gully. sidewalls and channell materials/ debris etc.
What is Upsole debris flow potential
Used of fans, transport zone and headwalls
What is water transport potential?
Used for fans, transport zones and headwalls
What is fan destabilization potential?
The potential for the stream channels on a fan to be destabilized, to widen or erode or avulse (breakout)
What is debris flow initiation potential?
Headwall failure potential
Sidewall failure potential
Gully geometry potential for debris flow hazard
debris flow initiation hazard
What are post logging conditions?
Evaluates the effect of harvesting on logging debris and sediment in the channel
rehab assessments
What are some management goals of GAP?
maintain gully wall and channel stability
maintain natural rates of erosion and recruitment and transport of sediment and woody debris
What is gully restoration?
- reduce volume of logging debris and sediment in gully. must be done immediately after harvest or the debris and sediment become part of the channel structure
- stabilize gully walls with vegetation
- protect sidewalls from stream erosion
- Road deactivation
What are some strategies of road deactivation?
- remove bridges, culverts
- construct fjords
- pull back fill slopes, stabilize road cuts
- re-establihs channel geometry+ hydrology
- armour channel beds
- clear woody debris immediately upstream and downstream of crossings
Terrain analysis
Description of the form and character of the land surface and the materials that underlie it
-past and present geological processes that modify the landscape
3 Rapid mass movement processes
- Debris slides
- Avalanches
- flows
Classification of landslide events is by the following:
-Failure mechanism
-depth of failure
-rate of failure
-water content
-material type
(rock, debris , earth, mud)
Landslide types:
Bedrock failures:
- Topple (slump)
- fall (material free falls)
- saskungen- sagging hillslope, bedrock slide
- creep
- slump
Pavilion earth flow
Old and very slow moving
-annual snowmelt recharges the groudn water to keep the slide moving
hummocky nature of the earthflow deposit
Debris flow
Material movement down channels as slurries of sediment, water and debris #1 worldwide-money+lives
Piping
Subsurface water erosion
-occurs in loose, non-cohesive materials overlying a stronger more cohesive material
Ravel
Dry process where the slope adjusts to its angle of repose.
Snow avalanches
Failure of large amount of snow on steep mountain. can often occur in the same paths as other failures
Landslide
Any mass of earth material (soil or rock) displaced by gravity
Criteria to delineate TSM classes
- slope gradient
- surficial material
- material texture
- slope morphology
- drainage
- geomorphic processes.
