a toolkit for identifying and measuring physical streams features from high resolution dems and...
Post on 22-Jan-2018
192 Views
Preview:
TRANSCRIPT
G EOMORPHOLOGICAL FEATURES EXTRACTION FROM HIGH RESOLUTION DEM S C.Cencetti, P.De Rosa, A.Fredduzzi.
OG
RS
201
4 ::
Ot a
nie
mi C
am
pus
, Aal
to U
n ive
rsity
, Esp
oo : :
10-
12 J
une
201
4
A toolkit for identifying andA toolkit for identifying andmeasuring physical streams featuresmeasuring physical streams featuresfrom high resolution DEMs andfrom high resolution DEMs anddigital imagedigital image
Authors: C. CencettiP. De RosaA. Fredduzzi
OG
RS
20
14
– O
tan
iem
i C
am
pu
s,
Aa
lto
Un
i ve
rsit
y , E
sp
oo
G EOMORPHOLOGICAL FEATURES EXTRACTION FROM HIGH RESOLUTION DEM S C.Cencetti, P.De Rosa, A.Fredduzzi.
The problem
● A river is a natural system characterized by continuous changes (in space and in time).
● In most developed countries, over the past decades, the morphology of most rivers have suffered huge changes, mainly due to anthropic interventions.
From Surian & Rinaldi, 2003
The anthropic effects usually cause a narrowing and incision of channel leading to a change of channel type.
Effects:Change in hydrograph response → flooding
OG
RS
20
14
– O
tan
iem
i C
am
pu
s,
Aa
lto
Un
i ve
rsit
y , E
sp
oo
G EOMORPHOLOGICAL FEATURES EXTRACTION FROM HIGH RESOLUTION DEM S C.Cencetti, P.De Rosa, A.Fredduzzi.
The Challenge
● Stream restoration has emerged as a means to improve aquatic systems by returning streams to their “pre-disturbed state”.
● So hydraulic work or any operation that affect the river should not (or al least minimize) the disturb to the system.
● Became fundamental understand the “equilibrium state” of a river.
– Fluvial geomorphologists are asked to answer the question: is the river/channel in equilibrium or disequilibrium?
Fluvial experts use indices as sinuosity index, braiding index, hydraulic discharge, bankfull limits to support their work comparing this values over time.
OG
RS
20
14
– O
tan
iem
i C
am
pu
s,
Aa
lto
Un
i ve
rsit
y , E
sp
oo
G EOMORPHOLOGICAL FEATURES EXTRACTION FROM HIGH RESOLUTION DEM S C.Cencetti, P.De Rosa, A.Fredduzzi.
How to compare this indices over time?
Which elevation is should use to derive indices as braiding index (number of channels), flow discharge .
??
Moreover what happens if we want to compare such indices over time remembering that the cross section change in time.
A reference elevation is required
OG
RS
20
14
– O
tan
iem
i C
am
pu
s,
Aa
lto
Un
i ve
rsit
y , E
sp
oo
G EOMORPHOLOGICAL FEATURES EXTRACTION FROM HIGH RESOLUTION DEM S C.Cencetti, P.De Rosa, A.Fredduzzi.
In the morphological-sediment study of a water course is useful to define a level (and a corresponding flow discharge) ”representative” (and responsible) about the shape and size of river channel. – Formative discharge.
Bankfull discharge
For a river in equilibrium state the formative discharge is the bankfull discharge or better is the discharge where streamflow spills onto the floodplain. [Leopold et al., 1964].
The flows effectively able to erode and shape the channel are not the low discharge (they flows through a channel) and not the highest discharge as they are capable of eroding the channel but they occur so infrequently. It is reasoned, therefore, that exists a range of intermediate discharges that do most of the work of shaping the river channel and that some summary value of these intermediate flows represents the formative discharge of the river (Wolman & Miller, 1960)
The formative discharge corresponds to a discharge with a return period between 1 and 3 years.
Bankfull elevation – bankfull discharge
OG
RS
20
14
– O
tan
iem
i C
am
pu
s,
Aa
lto
Un
i ve
rsit
y , E
sp
oo
G EOMORPHOLOGICAL FEATURES EXTRACTION FROM HIGH RESOLUTION DEM S C.Cencetti, P.De Rosa, A.Fredduzzi.
formative discharge – bankfull discharge
Bankfull channel ≠ Active channel
Thalweg
● Reconstructing streams to a pre-disturbed state is a difficult task as we know the landscape never return to its condition before human-disturbance
● We rely on accurate determination of the modern bankfull channel geometry to approach stream restoration projects.
Bankfulllimits
OG
RS
20
14
– O
tan
iem
i C
am
pu
s,
Aa
lto
Un
i ve
rsit
y , E
sp
oo
G EOMORPHOLOGICAL FEATURES EXTRACTION FROM HIGH RESOLUTION DEM S C.Cencetti, P.De Rosa, A.Fredduzzi.
The hub for all indices
#1: Bankfull discharge
Bankfull elevation
#2: Number of channels
#3: Bankfull width
#4: Hydraulic conveyance
The tool here presented is developed to extract such morphological feature directly from an high resolution DEM (LiDAR)
#5: Polygon of channel limits
OG
RS
20
14
– O
tan
iem
i C
am
pu
s,
Aa
lto
Un
i ve
rsit
y , E
sp
oo
G EOMORPHOLOGICAL FEATURES EXTRACTION FROM HIGH RESOLUTION DEM S C.Cencetti, P.De Rosa, A.Fredduzzi.
bankfull elevation
Bankfull location are identified on the following standard field indicators:● Break in bank slope corresponding with the active floodplain● High-flow markers
➢ Limit of bank scour➢ Roc k staining➢ Sand/silt deposits
● Vegetation limits● Bar tops
OG
RS
20
14
– O
tan
iem
i C
am
pu
s,
Aa
lto
Un
i ve
rsit
y , E
sp
oo
G EOMORPHOLOGICAL FEATURES EXTRACTION FROM HIGH RESOLUTION DEM S C.Cencetti, P.De Rosa, A.Fredduzzi.
bankfull elevation
The bankfull definition becomes difficult to apply in riverbeds recently carved or still in incision.It may happen that the "active floodplain" is absent and the bankfull discharge could be identified as a discharge where flow spills onto a “terrace”.
This flow may be associated with return periods that excess the 1÷3 years - does not correspond to the formative discharge
The bankfull definition becomes difficult to apply in riverbeds recently carved or still in incision.It may happen that the "active floodplain" is absent and the bankfull discharge could be identified as a discharge where flow spills onto a “terrace”.
This flow may be associated with return periods that excess the 1÷3 years - does not correspond to the formative discharge
OG
RS
20
14
– O
tan
iem
i C
am
pu
s,
Aa
lto
Un
i ve
rsit
y , E
sp
oo
G EOMORPHOLOGICAL FEATURES EXTRACTION FROM HIGH RESOLUTION DEM S C.Cencetti, P.De Rosa, A.Fredduzzi.
Cross section hydraulic magnitude
Vertical scale: horizontal scale = 10:1hydraulic depth=
wet areawidth
OG
RS
20
14
– O
tan
iem
i C
am
pu
s,
Aa
lto
Un
i ve
rsit
y , E
sp
oo
G EOMORPHOLOGICAL FEATURES EXTRACTION FROM HIGH RESOLUTION DEM S C.Cencetti, P.De Rosa, A.Fredduzzi.
The methodology
The idea behind the tool is based exclusively on the bank/floodplain slope break.
For each cross section, is graphed the hydraulic depth as a function of flow elevation.
The (local) maximum value of this function indicates a the elevation where water spills across the floodplain
(approach suggested by McKean &Wright 2005 as variant of Williams 1978)
OG
RS
20
14
– O
tan
iem
i C
am
pu
s,
Aa
lto
Un
i ve
rsit
y , E
sp
oo
G EOMORPHOLOGICAL FEATURES EXTRACTION FROM HIGH RESOLUTION DEM S C.Cencetti, P.De Rosa, A.Fredduzzi.
The tool
The tool developed is able to:
● graph the hydraulic depth vs the elevation
● investigate such function to locate the local maxima and select the first local max corresponding to the first break in slope.
OG
RS
20
14
– O
tan
iem
i C
am
pu
s,
Aa
lto
Un
i ve
rsit
y , E
sp
oo
G EOMORPHOLOGICAL FEATURES EXTRACTION FROM HIGH RESOLUTION DEM S C.Cencetti, P.De Rosa, A.Fredduzzi.
The tool
The tool developed is able to:
● graph the hydraulic depth vs the elevation
● investigate such function to locate the local maxima and select the first local max corresponding to the first break in slope.
OG
RS
20
14
– O
tan
iem
i C
am
pu
s,
Aa
lto
Un
i ve
rsit
y , E
sp
oo
G EOMORPHOLOGICAL FEATURES EXTRACTION FROM HIGH RESOLUTION DEM S C.Cencetti, P.De Rosa, A.Fredduzzi.
The methodology – limitation
ISSUE:1)We experienced that the
methodology work better in rivers with floodplain and would be limited in confined channels that miss floodplains.
2)The method is less definitive in channel with multiple terrace, where could be tricky decide which terrace and which plateaux in the hydraulic depth function correspond to the current bankfull elevation
A specific smoothing procedure is required to find the
“significant” local maxima(remove noise)
OG
RS
20
14
– O
tan
iem
i C
am
pu
s,
Aa
lto
Un
i ve
rsit
y , E
sp
oo
G EOMORPHOLOGICAL FEATURES EXTRACTION FROM HIGH RESOLUTION DEM S C.Cencetti, P.De Rosa, A.Fredduzzi.
The QGIS pluginThe tool have been implemented as QGIS plugin ant it have two main steps:1) Cross sections generation from river axis known longitudinal step and
width2) Evaluation of bankfull elevation (following the proposed methodology) for
each cross section and deriving of all morphological features.
In tab “Numerical setting” the user select the vertical steps and the minimum hydraulic depth.
1
2
OG
RS
20
14
– O
tan
iem
i C
am
pu
s,
Aa
lto
Un
i ve
rsit
y , E
sp
oo
G EOMORPHOLOGICAL FEATURES EXTRACTION FROM HIGH RESOLUTION DEM S C.Cencetti, P.De Rosa, A.Fredduzzi.
The numerical parameters
Vertical steps: it defines the number of points in function.+ High values are more sensitive for
small slope variations- High computational timeUsually > 500
Minimum hydraulic depth: this setting is to filter out local maxima below such value. Usually: 0.5 m
OG
RS
20
14
– O
tan
iem
i C
am
pu
s,
Aa
lto
Un
i ve
rsit
y , E
sp
oo
G EOMORPHOLOGICAL FEATURES EXTRACTION FROM HIGH RESOLUTION DEM S C.Cencetti, P.De Rosa, A.Fredduzzi.
The spline smoothing procedure I
A smoothing procedure, based on splines function, is required to remove local maxima not significant (“noise”).
● Explore the range 0÷1 for 100 smoothing parameter (spar).
● To select the best “spar” parameter a k-fold cross validation is used.
● For each “spar” parameter the mean square error and the 1sd is computed
Black dots represent the mean square error and the grey bar the 1sd
The spar selection
OG
RS
20
14
– O
tan
iem
i C
am
pu
s,
Aa
lto
Un
i ve
rsit
y , E
sp
oo
G EOMORPHOLOGICAL FEATURES EXTRACTION FROM HIGH RESOLUTION DEM S C.Cencetti, P.De Rosa, A.Fredduzzi.
The spline smoothing procedure II
A smoothing procedure, based on splines function, is required to remove local maxima not significant (“noise”).
● spar parameter with minimum error
● The corresponding 1sd
● The highest spar parameter, just smaller that 1sd, is selected
The spar parameter: 1)non significantly
different from the minimum
2)Big enough to smooth data and remove noise
OG
RS
20
14
– O
tan
iem
i C
am
pu
s,
Aa
lto
Un
i ve
rsit
y , E
sp
oo
G EOMORPHOLOGICAL FEATURES EXTRACTION FROM HIGH RESOLUTION DEM S C.Cencetti, P.De Rosa, A.Fredduzzi.
Evaluation of bankfull elevation
we found the local maxima looking for the zero function of 1st and 2nd derivative of spline using the newthon-rampson method.
The figure shows how The figure shows how this approach is able this approach is able to remove small local to remove small local maxima for a better maxima for a better identification of identification of bankfull elevationbankfull elevation
No selected No selected local maximalocal maxima
OG
RS
20
14
– O
tan
iem
i C
am
pu
s,
Aa
lto
Un
i ve
rsit
y , E
sp
oo
G EOMORPHOLOGICAL FEATURES EXTRACTION FROM HIGH RESOLUTION DEM S C.Cencetti, P.De Rosa, A.Fredduzzi.
Polygon limits for multiple channels
In case of multiple channel the tool locate the polygon limits to the channel with wet area max.
Channel limits
Banfull width
OG
RS
20
14
– O
tan
iem
i C
am
pu
s,
Aa
lto
Un
i ve
rsit
y , E
sp
oo
G EOMORPHOLOGICAL FEATURES EXTRACTION FROM HIGH RESOLUTION DEM S C.Cencetti, P.De Rosa, A.Fredduzzi.
The entire workflow
OG
RS
20
14
– O
tan
iem
i C
am
pu
s,
Aa
lto
Un
i ve
rsit
y , E
sp
oo
G EOMORPHOLOGICAL FEATURES EXTRACTION FROM HIGH RESOLUTION DEM S C.Cencetti, P.De Rosa, A.Fredduzzi.
Case study: Paglia River – central Italy
Reach of 2.2 km of length
XS step: 80mXS width: 400 m
OG
RS
20
14
– O
tan
iem
i C
am
pu
s,
Aa
lto
Un
i ve
rsit
y , E
sp
oo
G EOMORPHOLOGICAL FEATURES EXTRACTION FROM HIGH RESOLUTION DEM S C.Cencetti, P.De Rosa, A.Fredduzzi.
a
Case study: Paglia River – central Italy
Wandering river in a strong disequilibrium state.● Narrowing and incision
processes● Change in channel
morphology from a braided river to a wandering
● The old active floodplain works now as a morphological terrace
● The active floodplain is now inside the old riverbed, before the narrowing process started.
The blue line is the polygon output of the tool: refers to the limits of the main channel related to the bankfull elevation.
OG
RS
20
14
– O
tan
iem
i C
am
pu
s,
Aa
lto
Un
i ve
rsit
y , E
sp
oo
G EOMORPHOLOGICAL FEATURES EXTRACTION FROM HIGH RESOLUTION DEM S C.Cencetti, P.De Rosa, A.Fredduzzi.
Results: channel limits in detail
OG
RS
20
14
– O
tan
iem
i C
am
pu
s,
Aa
lto
Un
i ve
rsit
y , E
sp
oo
G EOMORPHOLOGICAL FEATURES EXTRACTION FROM HIGH RESOLUTION DEM S C.Cencetti, P.De Rosa, A.Fredduzzi.
Local incongruence?
Local incongruence (a) between main channel limits and aerial photo does not appear in the shaded map.
There is a shift in time between LiDAR survey and orthofoto date.
OG
RS
20
14
– O
tan
iem
i C
am
pu
s,
Aa
lto
Un
i ve
rsit
y , E
sp
oo
G EOMORPHOLOGICAL FEATURES EXTRACTION FROM HIGH RESOLUTION DEM S C.Cencetti, P.De Rosa, A.Fredduzzi.
Result: number of channels vs bankfull width
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 280
50
100
150
200
250
0
1
2
3
4
5
6
7
bankfull width channels
wid
th (
m)
# o
f ch
an
ne
ls
In a equilibrium river # of channel is proportional to the bankfull width.
The proportion looks altered.The floodplain is going to became a terrace.
OG
RS
20
14
– O
tan
iem
i C
am
pu
s,
Aa
lto
Un
i ve
rsit
y , E
sp
oo
G EOMORPHOLOGICAL FEATURES EXTRACTION FROM HIGH RESOLUTION DEM S C.Cencetti, P.De Rosa, A.Fredduzzi.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 280
100
200
300
400
500
600
700
800
900
1000
0
50
100
150
200
250
300
wet area
Bankfull di-scharge
m3
/s
Are
a (
m2
)
Result: wet area and bankfull discharge
A good correlation between discharge and wet area.
1)For some cross section the proportion is altered (see 13÷14 and 26÷27) – low bed slope
2)Section 1 has very higher value of area → high discharge
Q =χ⋅S⋅√R j
OG
RS
20
14
– O
tan
iem
i C
am
pu
s,
Aa
lto
Un
i ve
rsit
y , E
sp
oo
G EOMORPHOLOGICAL FEATURES EXTRACTION FROM HIGH RESOLUTION DEM S C.Cencetti, P.De Rosa, A.Fredduzzi.
Cross section #1
● The cross section look carved and in this point the river is partially confined (the floodplain in right is missing).
OG
RS
20
14
– O
tan
iem
i C
am
pu
s,
Aa
lto
Un
i ve
rsit
y , E
sp
oo
G EOMORPHOLOGICAL FEATURES EXTRACTION FROM HIGH RESOLUTION DEM S C.Cencetti, P.De Rosa, A.Fredduzzi.
Result: discharge variation and water table
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28-2
0
2
4
6
8
10
12
14
16
130
135
140
145
150
155
maxWTWT linear egressionvariation
As the discharge may be affected by global error, as the DTM LiDAR does not include the under-water, we should be more interested in variation rather that the discharge itself.
Potential pitfallXS # 26 → Increasing of cross section area.XS #1 → carved cross section.
OG
RS
20
14
– O
tan
iem
i C
am
pu
s,
Aa
lto
Un
i ve
rsit
y , E
sp
oo
G EOMORPHOLOGICAL FEATURES EXTRACTION FROM HIGH RESOLUTION DEM S C.Cencetti, P.De Rosa, A.Fredduzzi.
Conclusions
● Advantages
– The tool/plugin is designed to be extremely simple to use (a DEM input and two numerical parameters).
– The tool use a robust methodological approach.
– The bankfull limits are correctly located compared to aerial photo.
– Several parameters useful to evaluate the “state” of a river.
– Few tool that extract river morphological features exists already implemented in a GIS environment
● Disadvantages
– The methodology base the location of bankfull limits only on the slope/break in slope. Some other collateral indicators, from aerial photo (?), using image classification procedure could/should be inserted.
– The tool is less definitive for river that miss floodplain, or in strong disequilibrium, or for braided rivers.
OG
RS
20
14
– O
tan
iem
i C
am
pu
s,
Aa
lto
Un
i ve
rsit
y , E
sp
oo
G EOMORPHOLOGICAL FEATURES EXTRACTION FROM HIGH RESOLUTION DEM S C.Cencetti, P.De Rosa, A.Fredduzzi.
THANKS FOR YOUR ATTENTIONTHANKS FOR YOUR ATTENTION
The authors acknowledge Luca Scrucca for the collaboration in the The authors acknowledge Luca Scrucca for the collaboration in the the statistical smoothing procedure.the statistical smoothing procedure.
Plugin available at:https://github.com/pierluigiderosa/BankFullDetection
top related