RAINFALL-RUNOFF MODELLING ON SMALL PLOTS UNDER DIFFERENT LAND USES WITH A UNIT HYDROGRAPH APPROACH

(1)

RAINFALL-RUNOFF MODELLING ON SMALL PLOTS UNDER DIFFERENT LAND USES WITH A UNIT HYDROGRAPH APPROACH

Findeling , A.; Ruy , and Gaudu¹ ² ³

1

2 ,3 2 3

S.; , J.C.

CIRAD-AMIS - Program m e Agronom ie - 2 4 7 7 , avenue du Val de Montferrand - B.P. 5 0 3 5 - 3 4 0 3 2 MONTPELLIER cedex 1 - e_ m ail : findeling@ cirad.fr INRA - Unité de Science du Sol - Dom aine St Paul - Agroparc - F 8 4 9 1 4 AVIGNON cedex 9 - e_m ail : ruy@ avignon.inra.fr gaudu@ avignon.inra.fr

M odelling the rainfall-runoff transform ation on sm all plots rem ains challe ng ing. Two different approaches can be identified :

1 / fully m echanistic m odels m odelling spatially variable overland flow (e.g. Fiedler, 1 9 9 7 ) : as these m odels require a hug e quantity of data they are used only at the very local scale (m ²). M oreover, infiltration process and crop growth are poorly or not accounte d for.

2 / sim ple statistical m odels (e.g. Peugeot ., 1 9 97 ) : they can be used on sm all plots or on hillslope, but only runoff am ounts are sim ulate d, thus the hydrograph at the outlet can not be obtained.

!

^{et al}

We propose to use a statistical approach based on the Unit Hydrograph (UH) m odel to quantify the effect of different form s of land use on runoff. This m ode l has previously been used for watershed hydrology (Duband ., 1 9 9 3 ) : it is called F DTF, for Fisrt Differenced Transfer Func tion.et al

Material and m ethods : experim ental layout Material and m ethods : theory

[ ] l

ite r

L l

l∈ E R =G R

∀ 1.. ,

[ ] [ ]^{ite r}l ^{ite r}

L l

l∈1..,Q=m ⁻¹T F

∀

[ ]M^{ite r}T F^{ite r} Q= ⁻¹

















= QL

Q Q ...

1 [ ] [ ]

[ ] ^^















=

−

− 1 1 1

1 ...

ite r L ite r ite r

m m M

[ ] [ ]

(

M M

)

[ ]M Q

T F^{ite r}=^t ^{ite r}⁻¹⋅ ^{ite r}⁻¹⁻¹⋅^t ^{ite r}⁻¹⋅

ite r l ite r

L l

l∈ Q=n E R

∀ 1..,

[ ]L ^{ite r}l

(

^t[ ] [ ]^{ite r} ^{ite r}

)

^t[ ]^{ite r} ^l

l∈ E R = n ⋅n ⋅n ⋅Q

∀ 1.., ⁻¹

l j i K

j j l

i T F E R

Q 1

1 −+

= ⋅

=∑

l

Qi l

j

E Ri−+1

(2)

References :

Duband, D.; C h. O bled and J.Y. Rodriguez, 1 9 9 3 . Unit hydrograph revisited: an alternate iterative approach to UH and effective precipitation identification, , 1 5 0 ,1 1 5 -14 9 . Fiedler, F.R., 1 9 9 7 . Hydrodynam ic sim ulation of spatially variable overland flow. PhD Thesis, C olorado State University.

Peugeot, C.; M. Esteves, S. G alle, J.L. Rajot and J.P. Vandervaere, 1 9 9 7 . Runo ff generation processes: results and analysis of field data collected at the East C entral Supersite of the HAPEX-Sahel experim ent, , 1 8 8 -1 8 9 , 1 7 9 -2 02 . Journal of Hydrology

Journal of Hydrology

Results : experim ents

Cum ulative rain and runoff of event n° 10 (29/9/98)

0 2 4 6 8

2894.0 2894.5 2895.0 2895.5

Tim e (h)

Rain or runoff (mm)

Rain Runoff lote3 Runoff lote4 Runoff lote5 Runoff lote6

12345678

9 10 11 121 3 14 15 161 7 18 19 202 1 22 lote3 lote4 lote5 lote6 0 %

1 0%

2 0%

3 0%

4 0%

5 0%

6 0%

7 0%

Runoff Coefficient (%)

eve nt #

lote3 lote4 lote5 lote6

Results : validity of the m ethod

Results : m odelling

event 11 even

t 13.2 event 28 event 30 even

t 36

event 46.1 event 54 even

t 55

event 58 .2

e vent 72 .1

even

t 72.2 even

t 73.2 lote6

lote5 lote4

lote3

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

R²

0 % 1 0 % 2 0 % 3 0 % 4 0 % 5 0 % 6 0 %

RC (mm mm-1)

event 11 event 13.2

event 28 event 30

event 36 event 46.1

event 54 event 55

event 58.2 event 72.1

event 72.2 event 73.2

lote3 lote4lo te5lote6