Natural and Anthropogenic

choppedspleenMécanique

21 févr. 2014 (il y a 3 années et 3 mois)

56 vue(s)

Natural and Anthropogenic
Agents of Watershed Change

Natural Agents of Watershed Change

Floods

The San Antonio River and
Guadalupe

River converge during a flood.


Natural Agents of Watershed Change

Drought

Brummetts
Creek

in southern
Indiana

following 8
weeks

without
measurable

rain.

Natural Agents of Watershed Change

Fire

Natural Agents of Watershed Change

Hurricanes

Natural Agents of Watershed Change

Erosion and Sediment Deposition

How much

is natural??

Timber Harvesting


Sediment
production from
logging roads is
770
-
fold higher than
unlogged forests


30% due to surface
erosion


70% due to mass
soil failure

Agricultural Impacts


Channelization


Drainage tiles


Removal of riparian
vegetation


Tillage practices


Nutrient loss


Soil loss

Indiana Drainage Code


Enacted by state
legislature in 1965


Co. Drainage Boards and
Co. Surveys have authority


Must ‘maintain’ regulated
drains in county


Code specifies that all
vegetation may be removed
for proper operation of the
drain

Legal Drain

Cleaning

‘Uncleaned’

‘Cleaned’

IBI and Habitat Score vs. %
Forest Land Cover

From: Wang et al.
1997, for 134 sites
on 103 WI streams

IBI scores vs. Four Categories of Land
Use. Correlations with agriculture and
forest were statistically significant.

From: Roth
et al. 1996 in
Michigan
watershed


at 23 1
st



3
rd

order stream
sites

Potential Downstream Influences on
Upstream Communities

From: Pringle,
1997)

The Problem:


Sediment Deposition


Human disturbance causes sediment
deposition in streams


Habitat degraded


Decline in biotic integrity of stream


Restoration needed

David Starr Jordan

(IU President: 1885
-
1891)


Earliest published
comment on the
destructive effects of
sediments in streams
(1889)


Wrote about loss of
trout habitat in
Colorado due to
mining

Hydrology of Sediment

Transport

Equilibrium
Flow
Sediment
Load
Hydrology of Sediment

Transport

Deposition
Flow
Sediment
Load
Scour
Sediment
Load
Flow
Deposition
Flow
Sediment
Load
The Effects of Sedimentation


Habitat


substrate for plants


loss of benthic habitats


Macroinvertebrates



(60%< if TSS >120 mg/L over norm


Gammon, 1970)


interference with respiration


gilled macroinvertebrates


smothering


loss of interstitial space

The Effects of Sedimentation

Fishes


interference with respiration


gill clogging


53
-
77% > in O
2

consumption


loss of rearing habitat


emergence


visual impairments for feeding


move downstream to avoid sluicing (4.3 km)

Moving Sediment Downstream

Flushing Flows


Regulated Streams (dams)


General Uses


One time sediment release


Regular maintenance of regulated
streams


Benefits


Flushing out fines


Channel maintenance


Riparian habitat maintenance


Glen Canyon Dam
Controlled Release
of 1996



Max Q with dam =
34,000cfs



Ave. peak flow w/o
dam = 93,400 cfs



Released 45,000 cfs
for 7 days

The Fawn River

The Fawn River


Study
Sites

Study Sites


DNR Dam

Study Sites


750 W

Study Sites


Rock Dam

DNR Dam Release


May 18, 1998
-

Sluicing Event


Increased sediment flow


Anoxic pulse

The Fawn River

Total Suspended Solids in the Fawn River
(Rock Dam)
304
42
9
2.6
14.7
0
100
200
300
400
5/18
5/19
6/26
7/17
8/14*
Date
TSS (mg/L)
* measured 6
days after a
discharge event

Suspended Sediments

Sediments were deposited
up to 3 feet deep

The formerly pristine Fawn
River was a sludgy mess

Greenfield Mills
-

before

Greenfield Mills
-

after

Mussels were clogged and
smothered

Macroinvertebrates

Family Biotic Index (HBI)
4.6
4.33
3.8
3.81
0
1
2
3
4
5
26-Jun
17-Aug
Date
Value
750 W
Rock Dam
Fish Data


No live fish observed 5/19/98


27 dead fish observed at Rock Dam in 30
minutes


Dead fish had blackened gills


all adult fish

Many of the dead fish had
blackened gills

Dead Fish @ Rock Dam

Fish Species
Number Dead
Rockbass
4
Smallmouth bass
7
Largemouth bass
1
Walleye
2
Rainbow trout
1
Channel Catfish
5
Bluegill
3
other fish
1
carp
1
suckers
2
Options For Restoration
and Enhancement


Options for sediment removal.


Moving sediments

downstream


Remove them from the system

Moving Sediments
Downstream


Natural flow fluctuation


Flushing flows


Habitat alteration (In
-
stream structures)


Unregulated streams


After temporary discharge


Example:

Valley Creek, Minnesota
(Waters 1992)


Deposition decimated trout and invertebrates


2 years of natural flow variation eventually
cleaned bed


Trout and invertebrates recovered

Moving Sediment Downstream:

Natural Flow Fluctuation


What flow regime to use?


How big (magnitude)?


How long (duration)?


When (timing)?











Comprehensive summary of techniques: Reiser et al (1985) for the
Pacific Gas and Electric Co.

Moving Sediment Downstream

Flushing Flows

Magnitude


Three primary approaches


Hydrological


Use runoff records (200% mean annual Q)


Morphological


Use channel characteristics (1.5 year flood)


Sedimentological


Based on sediment transport equations

Moving Sediment Downstream

Flushing Flows


Timing


Fish and wildlife requirements


Spawning: biological cue, floodplain spawners


Rearing: juveniles in the floodplain


Riparian vegetation


Historical runoff period


Water availability



Moving Sediment Downstream

Flushing Flows

Considerations


Downstream effects


Sediments downstream


Disturbance of spawning gravel


Speed of flow release and recession


Quality of flush water



*Most successful in high gradient and riffles*

Moving Sediment Downstream

Flushing Flows


Most tested techniques


Used commonly for trout


Macroinvertebrates & other organisms benefit


Localized scouring


Goals for use of in
-
stream structures


Speed current and increase turbulence


Deepen channel


Increase substrate particle size

Moving Sediment Downstream

In
-
stream Structures


Techniques for localized scouring


Placement of roughness elements in stream


Wing deflectors


Temporary structures

Moving Sediment Downstream

In
-
stream Structures


Roughness elements


Boulders, stones and logs


Increase scour


Turbulence


Velocity


Habitat creation


Moving Sediment Downstream

In
-
stream Structures

Moving Sediment Downstream

In
-
stream Structures


Wing Deflectors


Triangular, embedded in bank, angled
downstream


Narrow and deepen stream


Increase velocity and scouring


Moving Sediment Downstream

In
-
stream Structures

Moving Sediment Downstream

In
-
stream Structures

Moving Sediment Downstream

In
-
stream Structures

Moving Sediment Downstream

In
-
stream Structures

Moving Sediment Downstream

In
-
stream Structures

Sediment Removal


Expensive


Disposal site


Large machinery required


Dredging


Gravel cleaning


Disturbance of contaminants


Gravel Gertie (Wash. State Univ.)


Self propelled tractor (log skidder)


Water jets angled down and forward


Hood collects flushed fines


Slurry concentrated (centrifuge) and
disposed of on banks


Sediment Removal

Gravel Cleaning

Sediment Removal

Gravel Cleaning

Recommendations for
Fawn River


Natural flow


Muck bars


Low budget


another ‘flushing flow’


Downstream effects


Dredging


Access problems