This document discusses a meeting held in Bari, Italy from September 22-24, 2009 regarding estimating the location of channel heads in a watershed using digital elevation models (DEMs). It presents several key assumptions about landscape geomorphology and erosion processes. Methods discussed include analyzing the DEM, slope-area plots, cumulative area distributions, and energy indexes to identify thresholds that indicate the transition from hillslopes to valleys and the start of the channel network. Results from applying these techniques to a pilot catchment in eastern Gargano, Italy are also presented.

1. Meeting in Bari • 22-24 September ’09
CChhaannnneell hheeaadd llooccaattiioonn
uussiinngg DDEEMMss
Autorità di Bacino della Puglia
LR 9 dicembre 2002
c/o InnovaPuglia S.p.A.
www.adb.puglia.it
Politecnico di Bari
Dipartimento di Ingegneria delle Acque
e di Chimica
www.diac.poliba.it

2. CHANNEL HEADS
EXTENT
OF CHANNEL NETWORK
Geomorphic
&
Hydrologic
Analyses
Environmental
Management

3. CHANNEL NETWORK OF APULIA REGION

7. Estimating channel head location
according scientific basis
KEY ASSUMPTIONS
Landscape
Geomorphologic form
Erosion
processes
DYNAMIC EQUILIBRIUM
between
SOIL PROPERTY
&
CLIMATE REGIME
Channel network rapresents indeed the mark on landscape
of intermittent discharge series of flow and sediment transport

8. Estimating channel head location
according scientific basis
KEY ASSUMPTIONS
Landscape
Geomorphologic form
Erosion
processes
DEM analysis
Dominant
sediment and transport
process
+
Geomorphologic thresholds

9. Estimating channel head location
according scientific basis
GEOMORPHOLOGIC
THRESHOLDS
=
¦ ( A, S)
Drainage Area
Drivers of erosion processes
Surface slope
But also
Indicators of past erosive actions

10. PILOT CATCHMENT
UTM Coordinate
E = 593735,06
N = 4638391,50
A = 27 SKm
BasA
EASTERN
GARGANO
Absance of tectonic forces
Soil impermeability
1.000
0.900
0.800
0.700
0.600
0.500
0.400
0.300
0.00000 0.20000 0.40000 0.60000 0.80000 1.00000
Ai / A
h i / h max
h media
MATURE
STAGE

11. DTM 5 x 5 m
Fill Dem
Slope
Flow Directions
Flow accumulation
Energy Index
TWI

12. SLOPE-AREA PLOT AvsP
1.000
0.100
TURNOVER
40 pixel
=
1100 mq
dS
dA > 0
dS
dA < 0
0.010
1 10 100 1000 10000 100000
Drainage Area [pixel]
Local Slope [m/m] n

13. [Gilbert]
slope-dependent
sediment transport
gives rise to
CONVEX PROFILE
Discharge and slope
dependent sediment
transport gives rise to
CONCAVE PROFILES
Transition from
CONVEX
to
CONCAVE
profiles
= Transizione
HILLSLOPE - VALLEY
NO!! Channel Head
AvsP
TURNOVER
40 pixel
=
1100 mq
dS
dA > 0
dS
dA < 0

14. AvsP
TURNOVER
40 pixel
=
1100 mq
dS
dA > 0
dS
dA < 0
Transition from
CONVEX
to
CONCAVE
profiles
= Transition
HILLSLOPE - VALLEY
NO!! Channel Head

15. 1.000
1,000
0.100
0,100
0,010
Area [pixel]
Pendenza locale [m/m]
potenza1
SA1
SA2
y = 1,2354x-0,3257 R2 = 0,3192
0.010
1 10 100 1000 10000 100000
Area drenata [pixel]
locale [m/m]
SA3
SA1 = 40 pixel
SA2 = 200 pixel
SA3 = 1100 pixel
AvsP

16. CUMULATIVE AREA DISTRIBUTION PLOT
1
0,1
0,01
0,001
1 10 100 1000 10000 100000
CAD2
A* [pixel]
P(A>A*)
CAD1
y = 0,5267x-0,4825 R2 = 0,9969
y = 11,685x-1,2068 R2 = 0,9994
potenza1
potenza2
SA1 = 40 pixel CAD1
SA3 = 1100 pixel CAD2
@ -0,43  fluvial channel
CAD

17. ENERGY INDEX DISTRIBUTION PLOT
1,000 10,000 100,000
1
0,1
0,01
0,001
0,0001
EI = S × A
Energy Index EI*
P(EI>EI*)
EID1
EID2
Slope-dependent
crtical contributing area
EID
A C cr =
(tanJ)2

18. EID
ENERGY INDEX DISTRIBUTION PLOT
1,000 10,000 100,000
EID1 EID2
2
5 . 0 2 4 ÷ø
1
0,1
0,01
0,001
0,0001
= × = Þ = æ
ö S
çè
P(EI>EI*)
EI S A A
2
5 . 0 10 20 ÷ø
Energy Index EI*
= × = Þ = æ
ö S
çè
EI S A A
EID1 EID2
Slope-dependent
crtical contributing area

19. EID CAD AvsP
1
1 10 100 1000 10000 100000
0,1
0,01
Area drenata [pixel]
Pendenza locale [m/m]
EID2
SG1 SG2
EID1

20. VERSANTI.basA: if(($tca.basA$<40),5,null)
VALLI.basA: if(($tca.basA$>=40)&&($EI.basA$<4),4,null)
HEAD.basA: if(($EI.basA$>=4)&&($ tca.basA$<1100),3,null)
RETICOLO.basA: if($tca.basA$<1100,null,2)

21. y = 351,38e1,4369x
R2 = 0,9741
y = 19,069e0,4895x
R2 = 0,9855
y = 151,08e-0,9204x
R2 = 0,9473
1.000.000
100.000
10.000
1.000
100
10
1
1 2 3 4
u
Nu,Lu*,Au
u vs. Nu u vs. Lu* u vs. Au
1^ legge di Horton 2^ legge di Horton legge di Schumm
25
20
15
10
5
0
0 0,5 1 1,5 2 2,5 3
t [h]
Q [mc/s]
RA
RB
RL
L
GIUH

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23. Bari, 24/09/2009