Looking at the hydrological results from the Asu catchment in a wider

context

Hodnett, M.G1., Tomasella, J2., Cuartas, L.A2., Waterloo, M.W1.,

Nobre, A.D3, Mota de Oliveira, S3. and Múnera, J.C3

1 VU, Amsterdam, 2CPTEC, INPE 3INPA, Manaus

Asu catchment results examined in a wider context Location (Landsat)

Area:

6.8 km2

Maximum elevation

95m asl

Maximum relief variation

~50m

Topography Dissected plateau, slopes up to 30%

Mean annual rainfall

~2400mm

Dry season (=less wet season!)

June – September

Geology Flat bedded unconsolidated sediments (sands and clays) of the Barreiras formation

Soils Oxisols (85% clay) on plateau Deep sandy soils in valley, transitional on slopes

Vegetation Terra firme forest (~180 species ha-

1, dbh >10cm)

Asu catchment results examined in a wider context Catchment information

– Rainfall– Runoff– Groundwater storage – Soil moisture storage– Interception– Evaporation fluxes– CO2 fluxes

In streamflow, groundwater, throughfall

– DOC– POC – Nutrients– CWD (coarse woody debris)

WATER TABLE

TDR PIT (15 m)DEEP SOIL MOISTURE (LOGGED)

DIPWELLS FOR WATER LEVEL

4.8 m ACCESS TUBES FOR SOIL MOISTURE (WEEKLY)

DISCHARGE, EC AND DOC MEASUREMENT (UV-VIS)

INTERFLOW PITS

TENSIOMETERS & THETAPROFILE PROBES AT RESPIRATION MEAS. SITES

INTERFLOW PITS

TENSIOMETERS & THETAPROFILE PROBES AT RESPIRATION MEAS. SITES

TOWER -CLIMATE - AWS

HEAT & CO2 FLUX -SONIC + IRGA

WATER QUALITYSAMPLINGWATER QUALITYSAMPLING

RAINFALL

Asu catchment results examined in a wider context Measurements

Asu catchment results examined in a wider context Cross-section along hydrological transect

0

20

40

60

80

100

0 100 200 300 400 500 600 700 800

Distance from stream (m)

Hei

gh

t ab

ove

str

eam

at

gau

ge

(m)

T12, 13

T8, 9

T6, 7

T4, 5

T3

T1, 2

STREAM

CROSS-SECTION ALONG HYDROLOGICAL TRANSECT

15M SHAFTwith TDR

DELTA-T PROFILE PROBES

INTERFLOW TRENCH

WATER LEVEL 16 JULY 2002

BOREHOLES

Asu catchment results examined in a wider contextSchematic diagram showing processes

Clay cap

50% clay

Throttle layer

Phreatic surface

In very large events only - possible return flow & surface runoff (in convex areas)

Groundwater discharge to stream

Variable contributing area

Main (perm. saturated) contributing area

Deep drainage/recharge

50m

Sand

Year Rain Baseflow % Stormflow % (mm) (mm) (mm)2002 2975 744 55 618 45

2003 2054 540 69 241 31

Asu catchment results examined in a wider contextKey features of Bacia Asu

• Deeply weathered and permeable catchment• Large storage in deep unsaturated zone (up to 36 m deep) • Large storage in saturated zone• Long time constant of drainage from this storage• Valley floor area ~35%

• kept near saturation by ground water discharge• main source of storm runoff (& DOC)

• Baseflow has very little DOC• Some evidence of contribution from slopes (in v. large

events)

Asu catchment results examined in a wider contextMoisture storage changes beneath the plateau

2200

2300

2400

2500

2600

2700

01/10/2002 31/12/2002 01/04/2003 01/07/2003 30/09/2003 30/12/2003

Sto

rag

e (m

m)

- N

B a

rbit

rary

zer

o

0

50

100

150

200

250

300

350

400

Dai

ly r

ain

fall

(m

m)

0 - 5m

5 - 15m

Daily rainfall

Asu catchment results examined in a wider contextStorage in saturated zone - Groundwater levels at different

distances from the stream

0

4

8

12

16

01/11/01 31/01/02 02/05/02 01/08/02 31/10/02 30/01/03 01/05/03 31/07/03 30/10/03 29/01/04

He

igh

t ab

ove

dat

um

(m

)

7m 67m 150m

215 m 272 m 403 m

510 m 780 m

0 – 230m - valley floor272 m - foot of slope403 – 780m - plateau

Asu catchment results examined in a wider contextRelation of stormflow to catchment area for studies near

Manaus

Catchment Years Area(km2)

Annual rainfall

Stormflow (%)

Source

Calado 1984-85

0.23 2870 5 Lesack (1993)

Barro Branco 1981 1.3 2312 9 Leopoldo et al.(1995)

1982 1.3 2365 9

1983 1.3 1949 9

Asu 2002 6.8 2975 45 Hodnett et al. (2004)

2003 6.8 2054 31

Asu catchment results examined in a wider context

Figure modified from Lesack (1993)

Asu catchment results examined in a wider context

Figure from Chauvel et al.(1987)

Asu catchment results examined in a wider contextCatchment form – DEMs from map and shuttle radar

Shuttle X-SAR Radar

Digitised topog. map MI 517/2

E

W

40

60

80

100

0 500 1000 1500 2000 2500

Distance (m)

Act

ual

hei

gh

t (m

)

E W

Asu

Bacia Modelo

Asu catchment results examined in a wider context Conclusions

• Results apply to deeply weathered permeable catchments

• Balance between storm flow and baseflow depends on proportion of catchment area which is valley floor with a shallow watertable

• Results from very small catchments cannot be scaled up directly without taking this into account

• Interflow / return flow on slopes may depend on presence of “clay cap” – not known how widespread this is

• Much geomorphological variation on the Barreiras sediments N of Manaus – range of valley forms in different areas.

Asu catchment results examined in a wider contextResults continued

• In areas with a shallow depth of weathering:

– much less storage

– less baseflow (quantity and duration)

– soil / weathered zone may fill to the surface creating very large contributing areas