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Volume 18 2), 220- 223, 2014JOURNAL of Horticulture, Forestry and Biotechnologywww.journal-hfb.usab-tm.ro

Dynamics of hydrological parameters in a small torrentialbasin covered with full-stocked forestsC. 11 D . M 11orne1 . rago1 .University of Suceava, Faculty of ForestryCorresponding author. Email: [email protected]

Abstract The paper is focused on how the ever-changing structure of the Key wordsforest canopy alters the hydrological parameters of a small torrential basin,where heavy rains may occur suddenly without being recorded atmeteorological stations, as happened in 99 and 1993 with Paraul Negruwatershed, where this study was carried out. The study consists in calculatingthe average annual load at the very beginning of five decades, from 1956 to2006, based on the forest stand description, provided by the forestmanagement plans, and the terrain features, plugged into a CAD system,where all important morphological features were estimated .Land use change is considered one o the nineboundaries o development Folke, 2013) , mainly dueto ecosystem services provided by forests. One o mainhypotheses hard to disagree with is the crucial roleplayed by forests in preventing floods , due the highretention capacity o forest canopy, litter and soil,combined with the capacity o forest trees to pump upthe water.The goal o this study is to show how the hydrologicalparameters o a full-stocked small watershed changeover time, even though the forest cover remainsunchanged, except for the age structure o the stands.Material and MethodIn a small watershed Paraul Negru, located in GuraHumorului forest district, the main hydrologicalparameters were estimated five times, taking intoaccount the slightly changes produced into the forestcanopy as described by each management plan

Fig. 2 Location o Paraul negru watershed

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The methodology actually addresses an intriguingquestion: may we have encountered extreme floodseven in a fully forested basin? In order to answer thisquestion, we have chosen a very small watershed,potentially torrential due to steep slopes, but almostcompletely covered with full-stocked forests andlocated pretty close to a meteorological station, whichhas provided most o all important meteorological dataneeded to estimate the hydrological parameters o thewatershed.

produced in a 50 years timeframe, period in which twomajor floods had occurred downstream: one in 1991and the next one in 1993, although the rainfalls in thosetwo periods, recorded at the nearest station GuraHumorului, 6 km distance), were not recorded as thehighest ones.

80.0.75.070.065.060.055.050.045.0

.035 030.025.020 0

j--

tt,_

- - l J- t- i_ -Fig. 1 Highest annual rainfalls in the studied period, asrecorded at Gura Humorului meteorological station


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secom:::...-:_ _

O. e:-:: ping the maps and data processing under~ ~ r o n m e n t - e::ing up a database with all relevant data about

s:ands lo ated within the watershed, for the period2e , \- en 19 -6 and 2006, data collected from the forest:::ianag rnent plans.In order to assess the hydrological parameters at thelosin g: section of the watershed two indirect methods\\ere p p l i in order to calculate the followingparameters: Z - total retention (mm); I soil infiltration(mm); Sc - run-off water layer (mm); Pl% rainfallwith 1 likelihood of occurrence ( ) ; i rainfallin tens ity for 1 occurrence likelihood (mm); Tc - timeof concentration; c - run-off coefficient; Qmaxlpeak discharge for 1 likelihood (m3/s ; Wa -sediment transportation;

Fig . 3 .Contour lines and hydrological network in ParaulNegru watershed

The runoff coefficient (c) has been determined by twomethods, Gaspar () and Freve1i () respectively, takinginto account the infiltration coefficient (ci) and theretention coefficient (cz , given that c= 1 c c;.In order to account for the stand structure whenassessing c,, we have used the procedure proposed by

Clinciu and Lazar (Lazar et Clinciu, 1987), based onstands hydrological mappin g, which fetches eachcompanme : in one of the four hydrologicalcateg:ories.. _ \_ 3. C. or D.The -hi_--c,- ---o ,- \1 appraised by the rat ionalefo rmul;_ \\ - - -:: s _:se oi :be potential evapo

::. _02d w2.:: --es ed using

esults

This study addresses two different aspects: the causes -te rain and the forest supposed to influence thetorrential patterns - and the effects, which are thehydrological parameters of the watershed. The firstparameter that brings about different hydrologicalcategories wherein the stand fall is the forest density,that changes, in average values, as shown in. Anotherfeature slightly changed over time is the forestdistribution on age classes, which reflects somewindtluows that had been produced meanwhile, asshown in; comparing the shares of the ages classes in1986 with the ones reached in 1964, one may considerthat a small area, about 20 hectares, was affected by\\indthrO\\-s. most of the stands getting older in normalconditions. meaning that influence of the age structurei n gligible .The wa er flO\\. and the solid load, assessed by indirectmethods. do not pose significant variations during the

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five decades period, except for a slightly increase ofthe erosion produced on slopes , brought about by

140

120 I' u (l it -; I a EVPI ~ ___

100

80mm

60 - - - ->-- - - -4020

f

Ill v VI VII V IXMonth x X XFig. 4 Average precipitation and potential evapo

perspiration, as given by at Gura Humoruluimeteorological station150

h100

50

01964 1976 1986 1996 2006

Fig. 6 Changes produced in age structure of the forest

Discussion and Conclusions

Between 1955 and 2006 the percentage of forest coverremained the same, 97,6 of the total area.hydrological role played by the forest, described by thefour hydrological categories within the stands of treesfell has showed a high hydrological effectivenessalthough the whole watershed might be included in thecategory of medium risk of triggering to1Tents whenexceptional heavy rainfalls occurred.Nevertheless the small change of solid load producedby slope erosion was brought about by small changesin the hydrological effectiveness of the stands, alteredduring the studied period, by salvage harvestingoperations and scattered windthrows.In spite of this hydrological reliability of thewatershed, two toITential floods yet had occurred in1991 and 1994, and the only cause of these two events

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sma ll er densities

ha 350=-=-E00150100 = -

1 .o-

964 1976 1986

of

111996

the stands.

t.t i 0 71 0 /1-I [2006

Fig. 5 Small changes in the forest density produced in thelast five decades

~ ... 12 --- - . .. .......__ rE

1008060

40

20

1964 1976 1986 1996 2006

Fig. 7 Average annual load (Wa) resulted from slopeerosion (Wav) and waterbed erosion (Waa)

shall be sought in the weak capacity of forestvegetation to buffer the water input, phenomenonwhich occurs only when the soil retention capacitydiminished, and this happened after snow melting orlong rainy periods, which are not recorded atmeteorological station for different reasons. This wasthe case of the studied watershed, where theappropriate forest layer couldn ' t deter two exceptionalfloods , produced downstream.References

I .Lazar, N. 1984 Contribut ii la studiul torentilor dinbazinul hidrografic S e b e PhD Teza de doctorat,Universitatea din B r a ~ o v2.Lazar, N . Clinciu, I. 1987 Determinareacoe ficientului de scurgere In functie de categoriilehidrologice de arborete, In bazinele hidrografice cu


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torentiale cu folosinta preponderent forestiera. InManuscris. I.C.A.S. u c u r e ~ t i .3.Idol T 2003 Hydrologic Effects of Changes inForest Structure and Species Composition. Manoa:Department of Natural Resources Environmental

Management Center of Tropical Agricultural andHuman Resources at the University ofHawai4.Folke C. 2013 Respecting Planetary Boundaries andReconnecting to the Biosphere . In State of the World2013: Is Sustainability Still Possible?

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