Runoffs and Phreatic Surfaces Behaviours over Large Floodplain and Lowland
Paddy Field
Sombat CHUENCHOOKLIN1, Tsutomu ICHIKAWA2, and Sanguan PATAMATAMKUL3(1: Graduate School, Khon Kaen University, Thailand, 2: Prof. Dr., Kyushu Tokai University, Japan,
and 3: Assoc. Prof. Dr. Khon Kaen University, Thailand)
Faculty of Engineering, Naresuan University, Phitsanulok, 65000 Thailand, E-mail: sombatc@nu.ac.thAbstract
Research of the exchange between surface and subsurface flows over large floodplain and lowland paddy field withinrecharge zone was carried out. A case study in the Yom River, Phichit Province, Thailand was selected to this researchduring 2001-2004. Field measurements of infiltration, flood depths and phreatic surface changes were observed during such
period. The water budget modeling and regression analysis were applied for fitting those comparative parameters. The
results showed that the relationships between the daily water tables and inundated depth were fitted with R2 approx. 0.90.
Those comparisons of the rising limb and recession limb hydrographs within the large flood year in 2002 and less flood year
in 2003 were presented. Baseflows were investigated according to time series of river flow and yielded R2 greater than 0.90.
Keywords: Surface-subsurface flow interaction, infiltration, phreatic surfaces, floodplain.

1. Introduction
In general the behaviors of surface flow andsubsurface flow over the catchment’s area are interacted
particularly in floodplain of large river. The hydrologic
phenomenon and parameters influencing phreactic
surface should be investigated. Infiltration from surface
may change the soil water storage and become theinterflow and groundwater as baseflow of the stream.
This paper described the effect of surface and subsurface
interaction in large floodplain paddy field.

2. Materials and Methods
Study Area
The catchment’s area of the Yom River in Phichit
Province, Thailand about 1,698 sq. km. was chosen tostudy surface runoff. Its basin covered by RID’s gauging
stations namely Y17 (Samngam) at upstream and Y5(Phothale) at downstream with a stream length of 71.88
km. (Fig. 1). It comprised of 7 sub-catchments
connecting the river with the average slope of 0.000337.
The core area of some 153.05 sq. km for studying runoffand phreactic exchanged was located in Phopratabchang
District in Phichit Province. About 60 % of this area isnormally affected by flood from the Yom River.
The core of study area is very flat slope of 0.000138 andaverage ground surface level of +32.889 m(MSL). Thereare 3-local streams via this area namely Phairob,
Nongkla, and Dongsualuang, respectively with averageslope of 0.000286 (Fig. 2). Most of land-use classifies byhigh-yield-variety (HYV) rice of 86% of total area thatgrowing into 2 times a year with depend on the amountof remaining water from the sources and inundated
seasons. Its geomorphology conforms by shallow clay orsilt layer at ground surface. Unconfined aquifer is thesecond priority source of water from farmer in order tosurvive the plants during lack of surface water which laysat the upper layer with average porosity of 0.26
(Mekpruksawong, 2004). There are 22-observation wells
ranged 15-30 m in depth in order to study the phreatic
surface behaviors (Fig. 3). The 15-observation wells

namely P3, P7, P8, P9, P10, P11, P12, P13, P14, P15,P20, P21, P22, P23, and P24, respectively were situatedon floodplain with the area of 50.41 sq.km.

Floodplain of theYom River

7-catchments forstudying surfacerunoffs

Core area

Fig. 1: Location of study area, sub-basins of the Yom

Fig. 1: Map of study area of the Yom River.

Fig. 2: The enlarger of core area (inner zone) used forstudying runoff and phreatic surfaces behaviors byexisting 22-observation wells.

The infiltration (I) was replaced by seepage coefficient( a c = K / H ) [mm/d/m] as the rate of infiltrated per headof ponded water above ground in case of soil surface issaturated (Mekpruksawong, 2004).

3. Results and Discussion
The result of field infiltration was averaged 1.355
mm/d (1.568x10-6 cm/s) with ac of 16.245 mm/d/m anddistributed over the study area presented in Fig. 5.

Fig. 3: Hydrogeological profiles and location of 22observation wells in the core study area (afterMekpruksawong, 2004)

Whereas Q can be calculated using existing water levelwith flow through bounded structures: Qin = volume of
upstream runoff included over-bank flow from the river,
Qout = volume of surface flow out the downstream, I =infiltration varied by t (measured from the fieldexperiment), and ∆S = change of water storages overfloodplain estimated by generated contour map. ET(based on FAO’s pan or Penman-Monteith method) canbe evaporation (E) during flooded otherwise ETcrop. I(t)by rainwater or floodwater above ground and ETcrop will
be recharged and withdrawn to and from aquifer whichleads to the change of phreatic surface.

ETP

The result of daily P, ETo, Qin, runoff and annual P, andETo over floodplain in the inner zone in 2000-2003 werepresented in Fig. 6 and Fig. 7. The phreatic surfaces
versus river stages were shown in Fig. 8 and Fig. 9.

300

0250

2040200

Rainfall
EToTotal RO vol.

150
100

60
80
100

50

1200140Fig. 6: Daily P, ET, total runoff volume on floodplain
and river channel in 2000-2003.

EQin

Qout

GWin

I
uplandFloodplainI
floodplain

GWLchangeRiver

Baseflow

GWout

Boundary of control tank

P, ET, I, Q (mm)Pumpingwells

ETo , Rainfall ;mm/d(1)Runoff vol. , 106 m3

I = (P-ET)+(Qin-Qout) -∆S

Fig. 5: The distributed infiltration flux (ac) on floodplain.

1/4/
01/ 08/1 / 00
12/0
1/ 0
4/
0
1/ 1
8/
1 / 01
12/0
1/ 1
4/
0
1/ 2
8/
1 / 02
12/0
1/ 2
4/
01/ 3
8/
1 / 03
12/0
1/ 3
4/
01/ 4
8/
1 / 0412/0
4Modeling and Parameters
The water budget model was applied for studying thewater balance in the cases of non-flooded and flooded
over the year round (Fig. 4). Rainfall (P) accounting overthe river basin is assumed to be disposed of as follows:surface runoff: inflow (Qin) at upstream and outflow(Qout) at downstream, evapotranspiration (ET), andgroundwater accretion as the following equation.

2000
1800
1600
1400
1200
1000
8006004002000

Rainf all2000

Fig. 4: Conception model as water budget for surface
and subsurface interactions was applied.

2001

ET (P-M)

2002

I-mm

2003

Runof fMean

Ye a rFig. 7: Annual P, ET, I, Qin in year 2000-2003

Fig. 8: Distribution of phreatic surfaces vs maximum
flood level of +35.00 MSL an example on 24/09/2002.

Water level, m(MSL)

36.00

RWLP14P7

34.00

P11P20P12P22

Delaytime atrising limb

32.00
30.00

Delay time atrecession limb

28.00

4. Conclusion and recommendation

26.00
24.00

Rising & recession limb ofRWL and GWL

22.00

1/11/0 1

31/3

/0 2

28/8/0 2

25/1/0 3

24/6/0 3

21/1 1/0 3

19/4

/0 4

Fig. 9: Comparison daily river stage (RWL) vs phreatic
surface (GWL) at each observation well in floodplain.

Elevation, m(MSL)a)y = 0.0905x - 3361.5
2R= 0.9451

33RWL

31

GWL
y = 0.0391x - 1439.9

292

R= 0.8986

2725
13/7/02

Elevation, m(MSL)

There are many parameters effect the change ofphreatic surface in floodplain hydrologic basin thatshould be paid more attention in the field observation andmodeling by using water budget or water balancetechnique. The result of the streamflow and phreatic
surface hydrograph can be used for further monitoring
and forecasting the effect of the change of groundwater
withdrawal.

References

3735

From the relationship of daily stages (RWL) versus
phreatic surfaces (GWL) in Fig. 9 and Fig. 10, the lagtime between rising and recession limbs of those RWLand GWL hydrographs in 2002 and 2003 were 75 days
and 105 days during rising limb, and 10 days and 6 days
during recession limb, respectively. The trend lines
during rising and recession limbs were fitted with
R2=0.90. The difference on slope of trend lines and timedelayed during rising and falling limbs were shown
because of flood volume and ponded time in 2002 wasmore and longer than 2003. The recession constant (Krb)for baseflow separation into groundwater flow (Krg) andinterflow (Kri) in 2000-2003 were fitted average of 0.783
and 0.936, respectively and R2=0.9672. The amount ofannual baseflow per total runoff via the measuring point
is average 10.7%. However, during dry season from midof January to May, there is zero baseflow in the river has
been obviously seen. Because of there is somewithdrawal water from users by using small pumping
machines along the river. The trend of baseflow is going
downward from that reason and also causes by overgroundwater withdrawal from farmer during drought
period.

2/8/02

22/8/02

11/9/023534- 1967.4b) y = 0.0528x
233
R = 0.9296
323130y = 0.0238x - 873.31
292
R = 0.9656
28272625
13/7/03
1/9/03RWL
GWL

Fig. 10: Trend lines of river stages (RWL) andphreatic surfaces (GWL) in a) 2002 and b) 2003.

Mekpruksawong P., Ichikawa T., Aramaki S., and Yamada T.,
Hydrogeological condition and groundwater behavior inlow land, Thailand, J. Japan Soc. Hydrol. & Water
Resour., 17(1), 32-42, 2004.
Chuenchooklin, S., Ichikawa, T., Mekpruksawong P., andPatamatamkul, S., The effect of flood changes onphreatic surface in large floodplain in Phichit, Proc. 2ndAPHW Conference 5-8 July 2004 Singapore, 1, 281285, 2004.