Ì . R a chner

2. N astavlenie gidometeorologitsheskim stanciam i postam. (1946): v ipusk 3, Tshast 1, Gidro-meteoisdat , Leningrad.

3. Pacifi c Southwest Inter-Agency Committee. (1966): L imitations in hydrologic data as appliedto studies of Water Control and Water Management , 129 ðð.

Some results of investigation and representationof snow supply and the melting of snow

Ì . Rachner, Meteorological Î ãï ñå,Ha11e, GDR

SUMMARY: Results of experiments to investigate and represent the snow-supply and the ablationof snow cover for the Selke catchment area up to the gauging station at Meisdorf are presented.M ethods of surveying snow cover are outlined. The ablation of àï î â cover is calculated by theaid of radiation measurements and the enregy budget . Special measurements (gradients ofclimatic elements) showed signifi cant local diff erences of snow-cover ablation. Finally, theimportance of the experiments with regard to water management and hydrology is discussed.

êéàî ì é : On pr6sente les r6sultats des expáriences dont le but est 4 '6tudier et de pr6senter les

donn6es concernant le stock neigeux et ÃàÛ àã|î ï de la couche de neige dans le bassin versantSelke j usqu' à la station de j augeage Meisdorf . On d6crit bribvement les ãï áãéî äåü appliquáes pourles reIev6s de la couche de neige. Ü'ablation 4å la couche de neige est calculde par la máthode dubilan de radiation et d'6nårgtå. Les mesures sp6ciales (les mesures de gradient des 6I6ments

climatiques) ont d6montr6 les é 1ãåãåï ñåâ locales considárables dans ÃàÛ àã|î ï de la couche deï ñ å . Enfi n on indique Ãí ï ðî ããàï ñå de ces exp6riences pour Ãèã|1üàã|î ï pratique des eaux etpour ÃÜó4ãî 1î à|å.

1. Ï ~1ÒÊ 0 13Ñ ÑÒ10 1~1

In the Selke river catchment area (à hydrometeorological experimental area in theHarz-Mountains) extensive investigations of water balance dependent on meteorologicalconditions are performed.

Áî ò å results of snow ablation measurements and computations at the end of the winterSeason 1965-1966 (February 1966) are discussed.

Meteorological measurements are performed at the base station of the observationsSiptenfe1de-Hanichen (ãð = 51' 38' .8 N ; Ë = 11' 05' .3 Å ; Í = 395 m above sea level ;

see also fi gs 1 and 2).

2. M EA SU R I N G M ET H OD S

Fig. 3 gives an impression of the measuring program. In addition to the measurementsand records at the station Siptenfe1de-Hanichen à network of secondary stations with

6 2 8

Áî ò å r esul ts of investi gati on and r ep resentation of snotv supp ly

4. Sz

5. G

6. À

QG

8õ

T ~

ò ~ , ß

àÜñå~ÊW~é ~

r

ðñ„Å

7. L

8.

9. S + 8ê ' 0 G À T4(a b 10 " L ) (1+ ~ ~ , ã.ç)

à ò 4

global radiat i on [ly m in ]atmospher ic back radiat ion [ly m in ]heat radiat ion [ly m in ' ]

(shor t-wave) coeffi cient of absorpt ion(1 — cz), where à is the albedotemperature of air [' Ê ]temp. of snow or soil sur face [' Ê ]8.26 10 [ly ' Ê min ]

0.8225 new constants of the A ngstrom-formula according to Bolz,

Falckenberg 1949

vapour pressure of the air [Torr]constant of cl oudiness (Bolz 1949)amount of clouds (tenths)constant of heat t ransfer (W armeii bergangszahl) [meal cm m in degr . ' ]

heat of vaporization [cal g ]atmospher ic pressurespecifi c heat of the air at à constant pressure [cal g ' degr . ]

max . vapour pressure at soi l or snow sur face temperat ure [T or r]— tzt. ( TÄ rt — Tz)

— (0.623r /ð ñð) uL (E — å )1 ð ä + ò 4( ~ b . 10 — " L ) ( I 1 óä ~ ã .5) ò 4 ~ ( ò ò

— (0.623ã/ð ñð ) tzL (E — å )

This equation is val id if we accept that t he stated r adiat ion-streams and heat -st reams

from and to the snow sur face are determ in, suff icient ly , the energy balance of the snowsurface. W hen the equation is suffi cient f or calculat ion, then we only have to measureor compute the fol lowing quant it ies (according to M ook 1965) :

i ; å~ ; t e., n ; Ô„ ; Q ; àã,; ÿ~

Special measurements and interpolat ions make i t possible to compute the dai ly andhour ly amounts of the energy balance. For our base stat ion Siptenfel de-H anichen dur ingthe snow melt ing per iod in February 1966 the components of the heat balance werecomputed for th is purpose.

Est imates of cloudiness and wind velocity were cor rected by observat ions at fi xed hoursat the neighbour ing stat ions. W ind velocity is the base to compute otz (constant of heattransfer ). V alues of uz appropr iate to the wind veloci t ies are contained in à work byH ofmann 1963 (the condi t ion of ground was considered).

Fr om the surplus of energy balance the amounts of ablation must be expl icable.A mbach 1966 has f ound in this way in the spr ing of 1962 à diff erence between calculat ionand measurement of 4.8 per cent (f or à glacier ).

F i gs. 4-6 give à summary of the meteorol ogical and hydr ometeorological elements

which form the hydro logical regime.The regime of snow melt refl ects factor s which

à) influence in some f orm the development of the snow cover ;Ü) express the development of the snow cover andñ) represent the resul t of snow cover ablation in relation t o meteorological condit ions.

6 3 1

Ì . Rachner

The reduction of snow-cover in the ï òåàéî ÷ happened very quickly (see fi g. 5). Thegradient measurements above the snow surface show that remarkable peculiar ities occurin the stratifi cation of vapour pressure. Heigel 1963 observed that air temperature and airhumidity in the layer close àÚî ÷å the snow surface show extraordinary and quickvariations.

Fig. 7 shows the result of the water balance of snow-cover and its eff ect on the waterbalance of the catchment area. Precipitation off ering (N iederschlagsdargebot) can beexpressed by the equation (according to Natermann).

10. N() = N — (R — Â),„ ,Ôå = " precipitation off ering"N = actual precipitation(R — Â),„ , „ = diff erence between accumulation and ablation of snow water storage

The water balance equation of the catchment area is therefore:1 1 . N p — — N — ( R — Â ) ãàï î í~ — — À + Ê + (ß — Â )

À = run off= evaporation

(R — Â) = underground water storage (R = " reserve ; Â = " consumption ")

The calculation of the energy balance actuates à part the " precipitation off ering" in

thaw water and direct precipitation. But an exact knowledge of the conditions of thesnow-cover (density of snow, structure of snow layers and snow crystals and contentof free water in the snow-cover) is necessary in this ñàâå.

¸ åã 1949 also observed that the depth of the snow-cover is very important for thevelocity of snow ablation. À low snow-cover for instance melts very quickly and thawwater in abundance becomes free in à short time. À high snow-cover on the other handis receptive of 1Üà÷ water.

According to the energy balance at February 19th and 20th, measured over meadow-land, between 20 and 30 mm water equivalent of the snow-cover must be reduced.From these 20-30 mm only about 10 mm have become free and the remaining amountis the liquid free water content of the snow-cover (about 30-40%). This is approximatelythe maximum amount (according to K usmin 1956).

A CKNOW LED GEMENò

1 am very grateful to my fellow worker, Mr. Horst Richter, for his linguistic revision ofthe manuscript .

R E F E R E N C E S

A MBACH, W. (1966): Untersuchungen des Energiehaushalts und des freien Wassergehalts heimA bbau der winterlichen Schneedecke. (Energy balance and water contents of the meltingsnow-cover). Arch. M eteor . Geophys. Biokl., Â 14, 2, S. 148-160.

ANGSTROM, À . (1916): M eteor . Z ., 33, S. 529.BoaR, W . (1949): D as Fruhj ahrshochwasser 1947 in Thii ringen. (The fl ood of spring 1947 in

Thii ringen). M i tt. Thii r . L andestoetterwar te, 8.Âî i.z, Í . Ì . (1949): D ie A bhangigkeit der , infraroten Gegenstrahlung von der Bewolkung.

(Connections between infrared contraradiation and the clouds). Z . M eteor ., 3, S. 201-203.BoLz, Í . Ì . und Åì õ êÿûââêñ, G. (1949): N eubestimmung der K onstanten der À ï äâ1ãáò âñÜåï

Strahlungsformel . (New evaluation of the constant fi gure in the ëÿ î âòâáì formula for radia-t ion). Z . M eteor ., 3, S. 97.

H EIGEL., Ê . (1963): Die Reif bildung und die schneenahen Temperatur-Feuchte-Verhaltnisse.(H oar-frost and events in the humid temperature zone near snow). M et. R., 16, 2, S. 46-49.

6 3 6

Runop condi ti ons duri ng snotv thawtng i n the M oravi an-Si lesi an Beski ds

HOFMANN, Ñò. (1963): Zum A bbau der Schneedecke. (On the destruction o f the snow-cover).Archi v M eteor . Geoph. Bi okl., Â 13, 1, S. 1-20.

Ê î ì ëêî ÷, W.D . (1947): Issledovanie vesennego stoka rek bassejna ã. Oka. (Investigation of springfl ow of rivers in the Î Ê À basin. Proceedings of the Central Institute of Forecasts). ÒòèéóÑ.1.Ð., 4 (31), 1947, ðð. 58-109.

Ê î êì ãì , P.P. (1956): Vodnye svoj stva snega. (Water properties of snow. Proceedings of theState Hydrological Institute.) Trudy G. G.l ., 55 (109), ðð. 41-69.

Ì î î ê, Í .G. (1965): Meteorologische Faktoren im Gelande nahe Tromso wahrend der Schnee-schmelze. (Meteorological factors during the ðåï î é of snow-melting in the area of Tromso).Ðèòå and Applied Geophysi cs (Pageophl , 60, 1, S. 201-216.

RACHNER, Ì . (1965): Der Wasserhaushalt der Schneedecke und seine Bedeutung im Rahmen desGebietswasserhaushalts der Oberen Bode (H arz). Eine Studie zur Hydrometeorologie. (Waterbalance of the snow-cover and the importance of it on the water balance of the area of theÎ Úåãåï Bode (Harz). À âãï éó on its hydrometeorology). Di sser tati on Uni versi tat, Leipzig

Êèï î é conditions during snow thawingin the M oravian-Silesian Beskids

V. Zeleny, Research Institute of AmeliorationPrague, Czechoslovak ia

SUMMARY A mong the causes of fl oods is thawing. Using the examples of runoff during thethawing in the experimental watersheds M ala Rhztoka and Cervik in the M oravian-SilesianBeskids it is proved that ø the mountain forested regions the thawing of âï î ú is usually quiteharmless and the culmination of runoff has not the character of à fl ood owing to the confi gurationof the landscape and of the presence of forests.

In the course of 13 years there has not been à single ñàçå recorded of any fl ood wave with àmaximum ãï ï î é above 367 1/â/kms.

êåâï ì é : Une des causes provoquant les crues est la fonte des neiges. En se basant sur Ãåõåò ð1åde Ãåñî ï 1åò åï ñ pendant la fonte des neiges dans les bassins versants exphrimentaux de M alaRhztoka et de Cervik en Beskids de Moravie et %16ç|å, il à 616 prouv6 que dans les rágionsforestihres de montagne, la fonte des neiges se fait g6n6raIement sans caIamit6s. Üà culminationd'6couIement ï 'à pas le caracthre de crue du fait de la confi guration du terrain et de la prdsence

des 1î ãåñç.Durant treize ann6es ñÃî Üâåã÷àã|î ï ç il ï 'à pas áñå enregistr6 un seul fl ot de crue à÷åñ un dhbit

sphcifi que maximum dhpassant 367 1/s/kms, bien qu'apparement toutes les conditions pour les

crues éï åâ à la fonte des neiges se soient produites particulihrement pendant les printemps 1962et 1963.

In many regions spring thawing mentioned as one of the causes of fl oods. This isçî in Czechoslovakia where there are some regions where spring thawing causes fl oodseach year and others in which they occur irregularly. Thawing in forest coveredmountain areas is harmless as à rule. Í åãå the intensity of thawing varies considerably

637