Use of tracer infiltration patterns for the parameterization of macropore flow p p p

U f t i filt ti tt f th t i ti f fl

Use of tracer infiltration patterns for the parameterization of macropore flow p p p

N.L.M.B. van Schaik* ⁽¹⁾ , dr. J.C. van Dam ⁽²⁾ , dr. R.F.A. Hendriks ⁽²⁾

•contact person: l vanschaik@geo uu nl

•contact person: l.vanschaik@geo.uu.nl

1)C t f G E l i l R h F lt f G S i Ut ht 1)Centre for Geo-Ecological Research, Faculty of GeoSciences, Utrecht

University, P.O. Box 80115, 3508 TC Utrecht, The Netherlands

2)Wageningen University and Research Centre Wageningen The Netherlands 2)Wageningen University and Research Centre, Wageningen, The Netherlands

Study area SWAP- model Parameterisation

The area chosen for the fieldwork is the Parapuños catchment

(approx. 99 ha) in Spain, near the city of Cáceres, Extremadura. The macropore parameters were calibrated using the tracer infiltration profiles, by

minimizing the difference between the measured and simulated curves of infiltration with The variably saturated water flow in the soil matrix is based on the Richards

(approx. 99 ha) in Spain, near the city of Cáceres, Extremadura.

The area is part of the Dehesas, a semi-natural landscape, which is typical for a large part of the south western Iberian Peninsula

minimizing the difference between the measured and simulated curves of infiltration with depth. The Mualem van Genuchten parameters for the soil matrix characterisation were equation, including terms for root water uptake and macropore exchange.

The soil hydraulic relationships are described according to van Genuchten.

typical for a large part of the south western Iberian Peninsula. obtained from Multi Step Outflow experiments. In the case of simulations with macropore

flow the fitted saturated conductivity of the MSO experiments was used. For the simulations The soil hydraulic relationships are described according to van Genuchten.

The top-boundary conditions are determined by precipitation, irrigation and

evapotranspiration y p

without macropore flow the much higher measured saturated conductivity was used, this was measured using a ponded water layer on the soil samples

Macropore concept:

evapotranspiration.

measured using a ponded water layer on the soil samples.

100 Pest runs show a small area with the best optimizations, with almost similar parameter

p p

The predominant feature of macropore flow is that precipitation and irrigation

sets, indicating that a unique set of best parameters can be obtained using the infiltration patterns for the optimisation.

water with solutes are routed into macropores at the soil surface, bypassing the

reactive unsaturated soil. This water is transported rapidly downwards and p p

The simulations of separate matrix and macropore flow with model parameters based on soil physical measurements and the infiltration patterns results in a much better prediction of

reactive unsaturated soil. This water is transported rapidly downwards and

distributed over different depths in the soil or the groundwater. The macropore

volume is characterised according to two properties: physical measurements and the infiltration patterns results in a much better prediction of measured distribution of infiltration with depth as compared to simulations without

volume is characterised according to two properties:

- continuity: internal catchment macropores versus main bypass

macropore flow macropores;

- persistency: static macropores versus dynamic (cracks).

O i i d ( i h 9 % i b d )

Catchment characteristics:

- agro-silvo-pastoral landuse; ^V st (cm3 cm-3)

F (-)

persistency: static macropores versus dynamic (cracks).

O ptimized parameters (with 95% uncertainty bounds ) V olume of macropores at soil

3 3

0.04 0.048 0.04 0.01 - 0.0

g p ;

- mediterranean, semi-arid climate;

poor soils (shallow acid

0.00 0.02 0.04

0

V

_mb V

ic

F ( )

0.0 0.5 1.0

0

surface, V _ss (cm ³ /cm ³ ) ( ±0.004) ( ±0.001) ( ±0.003)

Fraction of internal catchment 0.90 0.98 0.99 0.01 - 0.9

- poor soils (shallow, acid,

low organic matter content).

^-40

-20

ZAh Z_Ah

z (cm)

^-40

-20

m = 0.4 m = 0.1

at soil surface, P _ic (-) ( ±0.03) ( ±0.002) ( ±0.001)

Power –m, m (-) 10.0 1.69 4,01 0.1 - 10.0

z (cm)

80

-60

( )

-60

m = 10 m = 2.5 m = 1

( ±0.97) (±0.061) (±0.21)

Relative depth of S-parameter, 1.0 0.37 0.56 0.0 - 1.0

Z_ic

( )

-100 -80

Z_ic

-100

-80 ^{m = 10}

Measurements

p p

S (-) ( ±0.06) ( ±0.013) ( ±0.023)

140

-120

F = 1 − S

Z

S z

S = ⋅

In the Parapuños watershed meteorological data (temperature, humidity, net radiance, global

Soil moist re content and ater balance sim lations nder nat ral circ mstances

-140

Zst

Ah

Z Z

S S =

Ah

( ^S ) ^{Z Ah z m}

S

S ⎟⎟ ⎞

⎜⎜ ⎛ −

+

= 1

The macropore geometry is described using a

limited number of physical and shape parameters:

radiance, wind speed and –direction), rainfall, catchment discharge and sediment transport are

measured every 5 minutes as part of an ongoing measurement campaign. Further measurements for

Soil moisture content and water balance simulations under natural circumstances

( )

ic Ah

Z

Z S Z Z

S

S =

Ah

+ 1 −

Ah

⋅ ⎜⎜ ⎝ − ⎟⎟ ⎠

For both soil moisture content as well as water balance the simulations with macropores show better results the than simulations limited number of physical and shape parameters:

- Z _ah : Depth bottom A-horizon

h b l h d i

y p g g p g

this study existed of dye-tracer infiltration experimenents, soil pits with TDR-sensors and piezometer measurements

For both soil moisture content as well as water balance, the simulations with macropores show better results the than simulations without macropores. The soil moisture content simulations of the topsoil yield better results using the macropore model. The

dd j i il i t t t ft i f ll d d ll ith b th th d I i l ti ith t th

- Z _st : Depth bottom Internal Catchment domain - Z _st : Depth bottom Static macropores

piezometer measurements. sudden jumps in soil moisture content after rainfall are reproduced well with both methods. In simulations without macropores, the

high saturated conductivity values which are needed to ensure enough infiltration result in rapid percolation from the topsoil to

st p p

- V _st : Volume Static Macropores at Soil Surface P : Proportion of IC domain at Soil Surface

deeper layers. Therefore in the simulations without macropores the top soils do not easily reach or maintain the high water contents which according to the measurements do occur in the top soils

- P _ic : Proportion of IC domain at Soil Surface - m: Power m for distribution curve IC domain

i d d b A

contents, which according to the measurements do occur in the top soils. . - R _zah : Fraction macropores ended at bottom A-

horizon

Wetting of the deeper layers is too slow for

- S: Symmetry Point for freq. distr. curve Wetting of the deeper layers is too slow for

both the simulations with and without

Measurements were used in two steps:

• infiltration patterns are used for the

macropores. This indicates that there is more preferential flow to the deeper layers than is

• infiltration patterns are used for the inverse parameterisation of the

physically based macropore parameters

Rainfall distribution to matrix, macropores and surface runoff:

0 0,5 1

fraction of area stained (-)

p p y

calculated using the parameterization based on the dye tracer infiltration profiles Runoff

physically based macropore parameters in SWAP

2) TDR measurements and yearly water

As long as precipitation intensity is lower than matrix infiltration capacity, the precipitation is distributed over matrix and macropores equal to the ratio

0 5

0 0,5 1

)

on the dye-tracer infiltration profiles. Runoff amounts are well simulated with

2) TDR-measurements and yearly water balance are used for evaluation of model

f d ^l

the precipitation is distributed over matrix and macropores equal to the ratio of their surface areas. Once matrix infiltration capacity is exceeded the

i it ti ill fl i t th d ff t t A li ht

5

10

ro fi le (c m

l11v1 l11v2 l11v3

macropores, but strongly overestimated in the simulations without macropores, even

performance under ^natural

circumstances

precipitation excess will flow into the macropores and runoff starts. A slight delay in the infiltration to macropores occurs due to a resistance to inflow,

15

ept h i n pr 20 l11v3

average hor profielen

p ,

though these simulations were performed with the very high measured k sat values which depends on the macropore width. This resistance is very low and

usually a threshold ponding height must be exceeded before regular runoff to

20 25

de with the very high, measured k-sat values.

Conclusions

usually a threshold ponding height must be exceeded before regular runoff to surface waters starts. Therefore runoff into macropores is favored over

l ff Conclusions

• macropore parameterisation based on infiltration profiles works well

regular runoff.

macropore parameterisation based on infiltration profiles works well

• fitted parameters underestimate rapid infiltration to deeper layers

• runoff and drainage is better simulated using the macropore concept