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IX Convegno Nazionale dellAssociazione Italiana di Ingegneria Agraria

Ischia Porto, 12-16 settembre 2009

memoria n. 3-19

TI ME DOMAI N REFLECTOMETRY EVALUATI ON OF RAI NFALL

HARVESTI NG I N H I LLSLOPE MI CRO-BASI NS BUI LT AROUND

OLI VE TREES: FI ELD MEASUREMENT FI RST RESULTS

M. Previati, I. Bevilacqua, S. Ferraris, D. Canone

Dipartimento di Economia e Ingegneria Agraria, Forestale e Ambientale Sezione di IdraulicaAgraria, Universit degli Studi di Torino

SUMMARY

Micro-basins are slope managements built out of earth and stone on hillslopes around

cultivated trees (e.g.: olive trees) for the rehabilitation of lands degraded by water

erosion and for the rainfall plus runoff water harvesting in arid and semi-arid zones.

In this paper we discuss the results of an extensive experimental survey for the

comparison of soil water content for both inside and outside the micro-basins.

Measurements were taken after some rainfall events from January to December 2003 in a

hilly region of Central Tunisia.

Time Domain Reflectometry technique was used in this survey to measure soil moisture in

15 couples of soil profiles (inside and outside) at three different depths. Four different

soils have been considered: Cambisols, Kastanozems, Arenosols, and Calcisols.

The data analysis shows a significant improvement on the water stock given by this type

of management. The differences in water storage in relation with different types of soil,

depths, and tillage are evident but strongly connected to farm management. In optimal

conditions a 30% increase of average water stock has been pointed out. Whereas in

adverse natural conditions or bad farm management this amelioration can nullify or even

deteriorate the plant life condition.

1 I NTRODUCTION

The infiltration determines how much water will enter the root zone and how much

will runoff. The runoff can be considered as the portion of water that exceeds the

infiltration capacity. Hence, the rate of infiltration affects not only the water economy of

plants communities, but also the amount of surface runoff that can be collected

(Schiettecatte et al., 2005; Oweis and Hachum, 2006) and the risk of soil erosion.

Water harvesting systems for the runoff water collection and storage still represents an

interesting solution to resolve water scarcity in many part of the world (see for an

overview Oweis and Hachum, 2006; Schiettecatte et al., 2005; Frot et al., 2008).

Southern mediterranean regions are characterised by arid and semi-arid climates that

engender an unbalanced distribution over space and time of the water resource. Moreover,

in the last 50 years the demographic boom induced a population pressure increase with an

overexploitation of natural resources. In this context, agriculture still remains the greatest


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M. Previati, I. Bevilacqua, S. Ferraris, D. Canone, R. Haverkamp

consumer of water resources, by changing its typology from extensive to intensive.

Careful attention has been given to different typologies of watershed management useful

for the conservation of runoff water and to also limit soil erosion thanks to international

organizations such as the FAO with its soil and water conservation projects (FAO, 2004).Watershed management can be realized by little walls with semi circular forms made

out of soil or stone (or both) found within and on the hillside, around every cultivated

tree. These micro-basins are comparable to little barriers built on the slope with the aim to

retain water (and eroded soil) in situ, or, at least, to slow down the runoff water velocity

(Fig. 1). In this study soil and stones micro-basins built around olive trees have been

considered.

The farmers in this area have become aware of the economical gain generated by thiskind of management (Mancuso and Castellani, 2005). However, few hydrologicalevaluations of this kind of applications have been done (Boers et al., 1982; Sepaskhah et

al., 2003; Schiettecatte et al., 2005).

The objective of this study is to quantify by Time Domain Reflectometry (TDR)

measurements the soil water storage efficiency of micro-basins in relation to soil type,

soil depth, morphology, and tillage. A comparison for the different situations with and

without management, is presented with soil water content measurements conducted inside

and outside the micro-basins. Finally, some considerations about good practices to

enhance the micro-basins performances have also been presented.

2 MATERIA LS AND METHODS

2.1 Experimental site

Central Tunisia highland is known as Tell, that is an extension of Algerian Tell andis characterized by a semi-arid and arid climates. All the selected farms managed with

micro-basins were located in the Kairouan district. This area is characterized by an annual

rainfall of about 300 mm which gradually decreases from north to south down to 240 mm

(average over the last 35 years).

In this paper, 9 farms with one-year-old micro-basins and 6 with five-year-old micro-

basins, with walls made out of soil and stones, have been considered.

The one-year-old micro-basins were located on Cambisol,Arenosol, and Kastanozem

soils. These soils are respectively characterized as follows:

- Cambisols have a cambic horizon and very fine texture,

- Kastanozems have a mollic horizon with a moist chroma value of more than 2 to a

depth of at least 20 cm. (FAO, 1998),

- Arenosols have a sandy texture to a depth of at least 100 cm from the soil surface.

The five-year-old micro-basins were located in the Hajeb el Ayoun zone on Calcisol

soils (FAO, 1998). These are characterized by a calcic orpetrocalcic horizon within 100

cm of the surface.

The UTM coordinates are in the 32T zone, between 552825 - 577001 latitude and

3908596 3953207 longitude. They are shown for each farm on Table 1.

Moreover, field measurements were collected in order to evaluate slope, surface of the

catchment basin, stones upon the soil surface and rocky surface, soil labour, and

vegetation (Table 1).


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Time Domain Reflectometry evaluation of rainfall harvesting in hillslope micro-basins built around olive trees

The geographical position is depicted in Figure 1.

Table 1. Micro-basins locations and relative morphologic data.

Farmnumber

Soiltype

Latitude

Longitude

Slope(%)

Vegetationcover(%)

Stonesonsurface(%)

Tillage

Catchmentarea(m2)

Micro-basinare

a(m2)

1 Cambisols 568055 3949631 33 20 50 no 70 18.4

2 Cambisols 571371 3953207 27 15 50 outside (old) 36 12.5

3 Kastanozems 577001 3948214 14 5 40 no 51 29.3

4 Arenosols 568342 3942826 21 2 30 no 33 29

5 Calcisols 552852 3911191 16 5 70inside

(superficial)63 32.3

6 Calcisols 568622 3951355 26 10 40inside and

outside76 28.1

7 Cambisols 568567 3942923 9 2 40 no 346 27.3

8 Kastanozems 576781 3947481 19 20 80 no 51 10.8

9 Calcisols 553004 3911052 21 10 60 inside 35 22.8

11 Arenosols 567537 3941074 17 1 20 no 79 29

12 Calcisols 555357 3908596 18 5 10outside(recent)

35 13.8

13 Kastanozems 576715 3947598 10 20 25 inside 48 18.5

14 Calcisols 555831 3914163 12 10 40 inside 350 7

15 Calcisols 555561 3914424 5 10 80 no 40 7.3

16 Calcisols 552825 3911421 15 10 80 no 410 28.5


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Figure 1. The Kairouan district in Tunisia (North Africa). The enumerated micro-basins are in the

rural area of Haffouz, Hajeb el Ayoun, and Kairouan and they are partially included in a FAO

project for soil and water conservation.

2.2 Measurements

Soil and morphology parametersFor every micro-basin selected, two pedological profiles 1 m in depth were dug (one

inside and one outside the soil and stone wall). In every horizon the following parameters

have been evaluated: texture, structure, skeleton, colour, and organic matter. Catchmentbasin soil profile textures and organic matters for every micro-basin analyzed at three

different depths are shown in Table 2.

More over other data have been collected in order to evaluate slope, catchment basin

surface, soil surface stones and rock, soil labour and vegetal cover. See fig. 1.

Soil water contentMeasurements were carried out by connecting the three-wire probes to a Tektronix

1502 C TDR cable tester using a 50 coaxial cable and a BNC connection.

In this work the Roth et al. (1990) relation has been used for calculating water contentfrom permittivity.

The used probes were set up by two stainless steel rods (150 mm length) with a 5 mm

diameter spaced out by a nylon spacer at a distance of 50 mm.

Inside and outside the 15 micro-basins, measurements of soil water content were taken

in every soil profile by using a set of two-rod TDR probes inserted into the soil at the

following depths: 0.00-0.15 m vertically, and 0.30 m, 0.60 m horizontally. The survey

was conducted in two different periods: spring 2003 (February-April) and autumn 2003

(October-December). In conclusion, three repeated measurements were carried out for

every depth in each of the 30 different soil profiles.


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Table 2. Catchment basin soil profile textures and organic matter for every micro-basin analyzed at

three different depths. Data has been grouped in relation to the FAO (1998) classification and

profile depths.

Infiltration testsFalling-head single ring infiltrometer tests (e.g.: Lassabatre et al., 2006) have been

done using a PVC cylinder (110 mm in diameter) inserted into the soil and filled with 100

mm of water height. The infiltration time was recorded every 10 mm at each step in the

cylinder until the complete infiltration of water.

Infiltration tests were conducted on the soil surface in the micro-basins and out of

them with a total amount of 30 measurements.

3 RESULTS AND DI SCUSSION

3.1 Overview on the collected data

3.1.1 Soil water content

Soil type. Concerning about the efficiency in different types of soils, one-year-old

micro-basins located on the following soils: Cambisols, Kastanozems, and Arenosols and

have been taken into account. As shown in Figure 2, an evident improvement can be

pointed-out in a lot of soils by comparing inside and outside volumetric soil water

content.

SOIL TYPE

CAMBISOLS

KASTANOZEM

S ARENOSOLS CALCISOLS

% 1 2 7 3 8 13 4 11 5 6 9 12 14 15 16

Sand 39 31 83 27 51 63 87 93 71 40 73 75 54 57 77

Silt 37 28 5 53 28 20 5 5 18 35 16 13 28 31 21

Clay 24 41 12 20 21 17 8 2 11 25 11 12 18 12 20.2

O.M. 1.8 0.9 0.0 2.4 2.5 0.6 1.1 0 1.3 1.1 0.0 0.0 0.7 1.7 0.8

Sand 39 31 37 27 51 63 95 97 38 40 76 75 61 73 77

Silt 37 28 13 53 28 20 3 2 29 35 13 13 27 20 21

Clay 24 41 50 20 21 17 2 1 33 25 11 12 12 7 20.3

O.M. 1.8 0.9 0.2 2.4 2.5 0.6 0.3 0 0.8 1.1 0.2 0.0 0.5 0 0.8

Sand 27 13 37 97 96 36 39 76 75 69 73 67

Silt 47 35 13 1 2 39 34 13 15 19 20 29

Clay 26 52 50 2 2 25 27 11 10 12 7 4

SOILDEP

TH

[m]

0.6

O.M. 1.3 0.9 0.0

BED

ROCK

BED

ROCK

BED

ROCK

0.2 0.1 0.7 0.5 0.2 0.1 0.1 0 0


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Figure 2. Comparison between data collected inside and outside micro-basins in the 2003

measurement campaigns. All data are divided for the survey period and the different type

of soil. A) Cambisols, B) Kastanozems, C)Arenosols and D) Calcisols.

Cambisol soils are characterized by presence of fine materials and great depths (Fig. 2

A) with a consequent good retention capability that allows high quantity of water storage,

which can increase up to 100% compared with the outside soil. Its also interesting to

highlight the quantitative differences between the spring time and the autumn period that,in addition to quantifying the retention capability, also shows the functionality for the

high range of water content. This good aptitude to water retention allows a water stockincrease average value close to 30% (0.10 m3m-3)

Kastanozems (Fig. 2 B) fertile soils have loamy texture and a high quantity of organicmatter but, unfortunately, those presented in this study, also have a very thin soil

thickness. This implies a low water storage capacity with the consequent loss of great part

of caught water. This situation makes the slope management by micro-basins useless and,

at the same time, in this condition, water retention is influenced by many of the external

factors. This can explain the high variability values where the average value is close to

zero.

A situation similar to Cambisols can also be supposed forArenosols (Fig 2 C). In this

condition, the sandy texture narrows down the water retention capability, but an

improvement is still present. The water retention can increase over 100% (in volume), but

the average value highlight an improvement of about + 0.03 m3/m3 that represents the

20% of the total water stock.

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.00 0.10 0.20 0.30 0.40 0.50 0.60

Soil water content- inside (m3/m3)

Soilwatercontent-outside(m3/m3)

Spring data

Autumn data

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.00 0.10 0.20 0.30 0.40 0.50 0.60

Soil water content- inside (m3/m3)


Spring data

Autumn data

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.00 0.10 0.20 0.30 0.40 0.50 0.60

Soil water content- inside (m3/m

3)


Spring data

Autumn data

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.00 0.10 0.20 0.30 0.40 0.50 0.60


3)


Spring data

Autumn data

A B


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About Calcisols (Fig. 2 D),a good capacity has been found in this type of soils, but

only in case of proper tillage: measurements show soil water content average increase of

about +25% in case of appropriate management, down to -45% in case of incorrect

tillage.Farm management.Another investigation has been made to verify the influence tillage

has on the land. Five-year-old micro-basinsmade on Calcisol soils have shown a soil

positive evolution thanks to the fine particle soil retention. Likewise, this kind of soil can

show a hard limestone crust with the consequent inability of water drainage.

Finally, the wall conservation condition can be important on the hydrologicalimprovement. All these variability brought a garbled distribution of data (Fig 3A). As a

matter of fact, by analyzing in detail some of these data, the effect of a bad farmmanagement can be highlighted. Fig 3 B shows an incorrect tillage of the farm # 12,

where a plough on the catchment basin at a 30 cm depth nullified the micro-basins

improvement in consequence of the runoff decrease. This situation can still be aggravated

if this tillage isnt done inside the micro-basin because the hardening of the limestone

crusts can impede water penetration. Supporting this theory, Figure 3 B shows the good

micro-basin effect in springtime evolving in a severe worsening result in autumn due to

0.00

0.10

0.20

0.30

0.40

0.00 0.10 0.20 0.30 0.40


3)


Spring data

Automn data

0.00

0.10

0.20

0.30

0.40

0.00 0.10 0.20 0.30 0.40


3)

Soilwatercontent-outside

(m3/m3) Spring data

Automn data

0.00

0.10

0.20

0.30

0.40

0.00 0.10 0.20 0.30 0.40


3)

Soilwatercontent-outside(m3/m3) Spring data

Autumn data

Figure 3. Old micro-basins data. Figure A shows all data collected. Figure B and C show the

importance of a right farm management: in the left, the good effect of micro-basins (farm 12)

(spring data) became null in consequence of an incorrect tillage (autumn data). In the right, a

good management (farm 6) is able to improve the water stock in every season.

A

B C


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0

20

40

60

80

100

camb

[1]

camb

[2]

camb

[7]

kast

[3]

kast

[8]

kast[

13]

aren

[4]

aren[

11]

calc

[5]

calc

[6]

calc

[9]

calc[

12]

calc[

14]

calc[

15]

calc[

16]

Soil type

Time(min)

Inside micro- basin Outside micro- basin

3.2 Micro-basins water harvesting management

The success of rain water harvesting is related to the quantity of water that can be

collected from an area with defined meteorological conditions. Soil texture and structure,

soil moisture before each rainfall event, rainfall intensity and duration, but also catchment

size, soil compaction, tillage, stones and rocky surfaces can all strongly influence the

efficiency of the micro-basins. In a non-limiting natural condition the correct

management becomes the key factor to preserve the micro-basins functions.

On the other hand, a good soil aptitude to increase the water storage conservation

inside the micro-basin is needed, namely high infiltration and retention capacity. A useful

way to avoid evaporation could be to consider surface tillage to interrupt hydraulic

continuity after infiltration and improve infiltration velocity.

In case of thin soil depth or a very high deep percolation, it would be helpful to stock

runoff water in a farm tank in order to dispense it in function of soil storage capacity.

4 CONCLUSI ONS

In this study micro-basins slope management for rainfall harvesting has been

evaluated. Micro-basinsgenerate an improvement in water and soil conservation. In order

to quantify the water stock increase it could be useful to evaluate soil texture, soil

thickness, soil depth, tillage or even the presence of elements of disturbance like

limestone crusts or surface clay films.

TDR soil water content measurements have been made inside and outside micro-

basins to evaluate their improvements and provide new planning information.

Taking a broad view of the different soil types (classified by the FAO (1998) method)

the binomial Cambisol micro-basin shows a good aptitude to water retention with an

increase average value close to 30% (0.10 m3m-3). Analogously, a good capacity has beenfound in Calcisol soils, but only in case of proper tillage: measurements show soil water

content averages between +25% (farm 9 and 14) down to -45% (farm 12). Sandy texture

Figure 5. Comparison of infiltration test durations (10 cm of water column) conducted in the surface

horizon of every experimental site.


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ofArenosol soils limits the water retention capability with increases in soil water stock of

about + 0.03 m3/m3 that represents the 20% of the total stock. In this case, micro-basins

become helpful also in the soil conservation by retaining the fine soil particles in the

slope. Finally, for Kastanozem soils, good retention capacity can be supposed from soilanalysis, but their thin thickness nullifies every improvement..

The micro-basins efficiency is connected to both the preliminary planning and the

farmer management. The best situation detected for the micro-basins valorisation is

identifiable with a no tillage (or a minimum tillage) condition, to facilitate runoff on the

catchment basin surface, in opposition with a quite deep labour inside the micro-basin for

a faster water infiltration.

Acknowledgements. This work has been possible thanks to the FAO Project FAO GCP-TUN-028-ITA. A special thanks also goes out to the Tunisi Headquarters, their whole

staff, and the Kairouan displace unit. This work has also been funded by the project

PRIN2007: Misura sperimentale dei processi di interazione atmosfera-vegetazione-suolo

e modellistica numerica della loro risposta ai cambiamenti climatici.

REFERENCES

Boers, Th.M. and J. Ben-Asher, 1982. A Review of Rainwater Harvesting. Agric. Water

Manage., 5: 145- 158.

FAO/ISRIC/ISSS. World Reference Base for Soil Resources. Rome: World Soil

Resources Rep. 84. FAO, 1998.FAO Corporate Document Repository, 2004. Catching the Rain A Successful

Partnership Restores Drylands in Tunisia. Y5378/E.

Frot, E., B. van Wesemael, A.S. Benet, M.A. House, 2008. Water Harvesting Potential inFunction of Hillslope Characteristics: A Case Study from the Sierra de Gator

(Almenria Province, south-east Spain).Journal of Arid Environments 72: 12131231

Lassabatre, L., R. Angulo-Jaramillo, J.M. Soria Ugalde, R. Cuenca, I. Braud, and R.

Haverkamp, 2006. Beerkan Estimation of Soil Transfer Parameters Through

Infiltration ExperimentsBEST. Soil Sci. Soc. Am. J. 70:521532.

Mancuso T. and L. Castellani, 2005. Amnagement du Territoire pour la Conservation du

Sol et Agriculture Pluviale: Rsultats Economiques des Exploitations dans un PVD.

D.E.I.A.F.A., Dep. Note (Unpubl.) 120pp.

Oweis, T., A. Hachum, 2006. Water Harvesting and Supplemental Irrigation for Improved

Water Productivity of Dry Farming Systems in West Asia and North Africa.Agricultural Water Management80: 5773.

Roth, K., R. Schulin, H. Fluhler, W. Attinger 1990. Calibration of TDR for Water Content

Measurement Using a Composite Dielectric Approach . Water Resour. Res. 26:2267-

2273.

Schiettecatte, W., M. Ouessar, D. Gabriels, S. Tanghe, S. Heirman, F. Abdelli, 2005.

Impact of Water Harvesting Techniques on Soil and Water Conservation: a Case

Study on a Micro Catchment in Southeastern Tunisia. Journal of Arid Environments61: 297313.

Sepaskhah A.R., H.R. Fooladmand, 2004. A Computer Model for Design of

Microcatchment Water Harvesting System for Rain-fed Vineyard. Agric. Water

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