Groundwater contribution to a mountain stream channel , Hedmark, Norway.

SYLVI HALDORSEN, JENS-OLAF ENGLUND, PER J0RGENSEN, LARS A. KIRKHUSMO & DAG HONGVE

Haldorsen, S.. Englund, J-O., Jorgensen, P., Kirkhusmo, L.A. & Hongve, D. 1992: Groundwater contribution to a mounta in stream channel , Hedmark . Norway. Nor.geol.unders . 422.3-14.

The Skvaldra stream in Hedmark, Southern Norway is characterized ~y a stable baseflow . This baseflow is controlled by a significant groundwater supp ly from Quaternary deposits. The area was chosen for an attempt at quant ification of the basenow's three groundwater components: (i) ground water from numerous springs on a sprinq-honzon at the boundary between permeable sediment-flow depos its in the upper valley side and compact basal till depos ited along the lower part of the valley sides and the valley bottom; (ii) groundwater from aquifers in compact basal till. topographically lower than the spring horizon; (iii) deep groun dw ater from till or underly ing bed­ rock . Flood events in the Skvaldra are due to surface run-o ff, usually confined to the valley bot­ tom along the stream channel , or due to very. shallow subsurface interflow , with very little or no groundwater compon ent. Even when the baseflow is very low « 0.05 rn's" ), groundwater from the springs makes up more than 70% of the total flow. Groundwater from the compact till constitutes about 10% of the baseflow, while deep gro undwater makes up less than 20%. During the summer the spring component is higher. During a year the baseflow varies between 0.03 and 0.1 rn's'", Most of this baseflow is due to groundwater, and the groundwater component is at least 1 x 10' m' per year, corres ponding to 10% of the annual precipitation .

Sylvi rtetaorsen. Per Je rqensen, Jens-Olaf Englund, tnstitutt for jord fag, seksjon for geologi, Nor­ ges landbrukshogskole, Postboks 28, 1432 As, Norwa y. Lars A. Kirkhusm o, Norges geologiske underseke tse. Postboks 3813 - Ullev;jl Hageby, 0805-0510, Norway. Dag Hongve, Statens institutt for toncenetse, Geitmyrsveien 75, 0462 Oslo 4. Norway.

Introduction in chemical and isotopic ratios of flow compo­ Terr ain covered by till or with a surface of nents. Observations from limnigrammes give strongly frost-weathered bedrock characteri­ some information about the hydrological pro ­ zes the mountainous regions of south central perties of a catc hment. but these cannot be Norway. In some mountain a: eas the ground­ anything but qualified guesses wit hout field water contribution to streams and rivers is studies. Hewlett (1982) stated that «no graph i­ considerable. It gives a stable and significant calor mathematical operation performed on a baseflow and has an important influence upon hydrograph will reveal the sourc e or pathway the chemical composition of these waters. The of stormflow». Different comb inations of sour­ routing of water along surface and sub-s urfa­ ces and pathways can lead to quite similar ce flow paths in such mountainous areas is hydrographs. This study, therefore, uses che­ important because it influences the timing of mical data in addition to the volume, rate, and strea m flow and the chem ical composition of timing of streamflow to clarify the sources of water reaching the stream. In a catc hment ground water and the specific pathways along consisting of fractured bedrock over lain by which grou ndwater moves through a catch­ glacial sediments, the rivers may receive wa­ ment. ter from deep regional groundwater flow paths The Skvaldra catchment in Hedmark was as well as shallower water from the glacial selected for the study because the Skvaldra overbu rden. Two general approaches have stream receives groundwater from thick Qua­ been used to better define the sources and ternary depos its along the valley sides and actual flow paths of wate r in catchments (e.g. because human influence is small. It is therefo­ Horton 1933, Pinder & Jones 1969, Kirkby re well suited for an attempt to quantify the 1978, Germann 1986, Kennedy et al. 1986. different groundwater components which con­ Sklash et al. 1986); (i) physical observations tribute to the Skvaldra 's streamflo w. The inves­ fro m field stud ies, coupled with theoretical flow tigation is mainly based on data from the peri­ modelling. and (ii) measurements of changes od 1987 to 1991. 4 By/vi Ha/dorsen, Jens-Ote! Eng/und, Per Jerqensen, Lars A. Kirkhusmo & Dag Honqve NGU· BULL. 422. 1992

Study area coming from the east. In the western part of the catchment there are two small lakes (Fig. 1). The annual precipitat ion is about 1100 mm Topography, climate and land use (Fig. 2).Winters are norm ally cold with tempera­ tures well below aoe , and the snow falls from The study was car ried out in the uppe r part the beginn ing of November. The main sno w of the Skvaldra catc hment , Godlidalen, whi ch melt period is usua lly in the latter part of covers 13.5 km' (Fig. 1). Godlidalen is an asym­ May. Two of the study years, 1989 and 1990, metric valley with a rather flat valley floor, were exceptionally mild, with little or no snow bounded by mountainou s areas to the north accum ulation until late December and wit h the and east, and low er hills between the Skvald­ main snow melt in late April. ra catch ment and the main Astdalen valley to Peatland const itutes about 40 percent of the west. The altitude varies from 875 m abo­ Godlidalen, and dom inates completely below ve sea level (a.s.l.) in the valley bottom up to the timber line. The Skvaldra catc hment is 1090 m at the highest mountain summit in the used only for extensive graz ing by sheep, east. The Skvaldra stre am forms a dend ritic hunt ing and recreation. Other sources of pollu­ pattern , with most of the tributary streams ion are insignificant.

Precipitation (mm) 70

60

'---'_---''----'3km 50

40

30

20 '

~ . ., I " 10 . 00 . : • I ° • f ' .. 0 ~ ~ ! : :-~ ~ ~~ ~ - ~:. ~:- ~~~~ ~ _ h _ ~ ! , · : o • • •• • •-', . .. • ,_: ... • .:. ". : ;,:: i ;.. ;. .. JFMAMJ JASON D

Discharge m 3s -' 20 -

...-/ Sk val d r a ca tchm ent

Monitored pa rt of 15 · ca tchment area River

o Gr ound w at er tu bewel l o Y Pre cipitation g auge

""'V Limnig raph

Peat lands 5

Sprin g horizon

Fig. 1. The Skvaldra catchment with position of the monito­ red part (Godlidalen). The profile a - a' is shown in Fig. 4. o J F D The western tube well is number 15006, the middle one 15007 and the eastern one 15008. Inset: 0 .d.= 0 sterdalen, Fig. 2. Precipitation at Sjusjeen 1990 and discharg e of the G.d.= Gudbra ndsdalen. Skvaldra in 1990. z - -<..------1 k m o C Dommant ground w a ter aJ oE- recharge ar ea ~ C r: Thin sacrments r c. and frost .. · Permeable weathered bedroc k !" -o· glacial seo tments '" -o· c I uva m a.s .t s ~· 1100 '" ~ 1050

Comp act basal (Ill 1000 Permeable and peat land sediments 9 50

900

"I--''-----LJ...... :,I!:l ""''' '-''-' c=. .,..J: ==c-=~-- _r. ---__,_- --,_--N..J 8 50 o 500 1000 1500 2000 2500 3000m ~=~ ~======a a' l .-- -;r I : ,;;:/ 1 - 3· Bas e flow 4 Flood events '0 --- j~ 7 .r: Tate ru ngskampen "

==== peat Spri ng A ­ unsaturated flow

Spring s saturated flow

-- - groundwater level

springs

Fig. 3. Depositional mode l for the Quatern ary sediments in Fig. 4. (a) W5W -ENE geo logical and hydrogeological pro file the Skva ldra catchment. a -a' through the southern par t of the Godlidalen based Top : Relation to the glac ier during glaciation. on the seismic investigations of Hillestad (1990). Position Bott om : Present day, show ing pos itio ns of the springs & of profi le is shown in Fig. 1. (b) Main hydrological budget peatland s. of the Skva ldra . 6 Sylvi Haldorsen , Jens-Olaf Englund. Per Jerqe rtsen, Lars A. Kirkhusmo & Dag Hongve NGU · BULL. 422. 1992

Bedro ck geology en clearly separ ated flood events, and it is The Skvaldra catchment is situated in the normally between 0.03"and 0.1 m's-I (Fig. 2). middle of a Late Precambrian sedimentary The annual baseflow is 1 - 3 x 10' m' , corre­ rock basin. The bedrock belongs to the upper sponding to 110 - 220 mm (Le. 10 - 20%) of part of the Brett urn form ation and consi sts the precipitation. During snowm elt floods , the of alternating fine-grained conglomerates and discharge in the Skvaldra can reach 20 m's-I. arkosic sandstones (Siedlecka et al. 1987). During the summer, stormflows of more than Seismic studies (Hillestad 1990) showed that 2 rn's' have been measured. the bedrock underlying the Quaterna ry sedi­ ments can be regarded as only moderately fractured,Le. with seismic velocities betwe en 4500 and 5500 ms-I. Monitoring The precipitation in summer was measured Quaternary geology with a Plumatic precipitation gauge (Fig. 1) The valley botto m and the lowest part of the and the data was proc essed by the Norwegian valley sides (about 6.5 km') are covered by a Meteorological Institute (DNMI Station 0676 compac t silty basal till of thick ness c. 10 m Astdalen - Skvaldra). During the winter, precipi­ (Kehler 1985, Hillestad 1990) (Figs. 3 & 4). Its tation data from the meteoro logical station at petrographic and granulometric composition Sjusjeen, 30 km west of Godlidalen, were is very homoge neous because it was formed used (DNMI Station 1296 Sjusjeen - Stora­ by comminution of the arkos ic bedrock alone sen). The precipitation data from Sjusjce n are (Haldorsen 1982, 1983). Glaciofluvial material almost the same as those from Godlidalen is found locally along the Skvaldra and this during the summer and fall, and it is therefor e is probably underlain by till. Bedrock expos u­ assumed that they are also representative for res are almost absent. the winter period. The upper part of the valley sides (about 7 The discharge of the Skvaldra was measu­ km') is covered by a 5 - 10 m thick layer of red with an Ott limnigraph (Fig. 1). Glaamen more permeable and less compact materia l, og Laagen Brugseierforen ing was respo nsible much of it unsorted. Debris flow deposits for the instrumentation, and the limnigrammes dominate. The sediments as a whole are in­ were analysed by the Norw egian Water homogeneous and form a hummocky surface . Resources and Energy Administration (NVE Meltwater channels are frequent, and in many 2673-0). of these only coarse boulder lags remain. For spring A (Fig. 3) the discharge was Some of the channels extend deep into the till. measured each time a water sample was col­ The distinct boundary between compact till lected , while for spring B (Fig. 3) the dischar­ and more permeable material can be followed ge was monitored closely only during two at an altitude of 950 m in the south up to shorter summer periods. The discharges of about 1000 m in the northern part of God­ these spr ings were measured with a tipping lidalen, where it continues into a prominent bucket or a bucket and a stop watch. moraine ridge. The boundary marks the upper Three groundwater monitoring tubewells of limit of an active glacier during the Weichseli­ 5/4" diameter and with a filter tip of one me­ an period (Fig. 3). Compact till was then depo­ tre length were placed in the till by the Geologi­ sited subglacially, while the material along the cal Survey of Norway (Fig. 1)(LGN Station ice-free valley sides was exp osed to water 24/Astda len 15006, 15007 and 15008). Ground­ sort ing, flow and frost activity. water levels in these were measured with a Above an altitude of about 1050 m the co­ manual measuring tape . ver of Quaternary sediments becomes thinner and the summits are characterized by boulder fields, formed by intensive fro st activity, pro­ Groundwater types and ground­ bably during a period of periglacial climate. water chemistry The main groundwate r recharge areas are the General hydrology of the Skvaldra area of frost weathered bedrock at the top The baseflow of the Skvaldra is defined as of the mountains and the permeab le sedi­ the lowest discharge which is observed betwe- ments along the valley sides (Fig. 4). Lower NGU - BULL. 422, 1992 Groundwater contribution toa mountain stream channel 7

A , Winter - March 1989

JJ Eq v/ 1 Skvaidra 5001

Spring 400 C

150 08 Spring 300 8

Spring A

15007 le ge nd '00 Snow H ' . HC0 3' Ca" Mg" N0 3- K' SO;' I Na' Cl Springs Sk Tub ewens in till

8. Summe r - August 1990

JJ Eqv ll 400

Spring C 150 06 JJ Eqv/ l

300 1500 Skvalora

Spring 8 20 0 1000 Spring A 15007 100 · 'IlI I 500 Rain ~ OL ~du,d OL Springs Tub eweus in till

Fig. 5. Ion composition of the main water types in Astdaten. Precipitation (Pl, groundwater springs A, B and C, Skvald ra, and grou ndwater tubewells 15008, 15007 and 15006. Bars on left show cations and bars on right show anions.Winter data are from 1989 . Summer data are from 1990. down , the peatlands form an effective barrier suggest that the hydraulic conductivities of against gro undwater recharge, Three main these sediments may be up to one hundred groundwater types dom inate (Fig. 4a, 4b): times higher than those of the compact basal (i) Groundwater in the inhomogeneous per­ till lower dow n. The groundwater in these meable sediments along the upper part of the upper sediments discharges via a marked valley sides. Data from Haldorsen et al. (1983) spring horizon (Figs. 1, 3 & 4)(Kehler 1985). 8 Sy/vi Hetoorsen , Jens-O/af Eng/und. Per Jerqensen, Lars A. Kirkh usmo & Dag Hongve NGU- BULL. 422, 1992

The springs are classified as cont act springs. since they occur at the bound ary between the SUMMER

S \f e>' w a : ~ S permable upp er sediments and the compact el'la.,,,,,, basal till. The spring water follows numerous U ECIIceree-a ne small stream s from the spring horizon down ~ Eo PO· ...•• '" -. to the Skvaldra. ~ "" (ii) Shallow groundwater in the basal till along ~ .. the lowest part of the valley sides and in the So- -0 .. valley bottom. This water discharg es along the valley bottom . Some discharge may occur from S S y e :...:.' Ye :"" . :. ' the till to the peatlands. but the main part ct1ann C " a" ~e' probably flows from the till directly to the c " Skvaldra. ... '" (iii) Deep groundwater in the lower part s of the till or in the bedrock. with a long residen­ 5m ce time. which discharges in the middle of the valley (see Englund 1986). From a conceptual standpoint. flow systems Fig. 6. Mod el of spring A (shallow qroun dwa ter) and Its relation to the meltwater channel. For pos ition of spring A in catchments can be cons idered to fall betwe ­ see Fig. 3. en two end-member extremes; those that are dom inated by near-surface flow paths and A. Hummoci< y area those that are dominated by deeper groundwa­ ter flow paths (e.g. Peters & Murdoch 1985. Parsons et al. 1986. Winter 1986. Baron & Bricker 1987). The bedrock in Godlidalen is resistant to - chemical weathering and mos t of the ground­ ------::::-:::: -::::-::::-::::-::::-/. water has a rather short residence time. The area is dominated by near-surface flow paths . As a result the groundwater which discharges B. into the Asta (Fig. 1) has a low ionic strength Hummoci< y area (Fig. 5) compared with other types of Nor­ weg ian groundwater (Englund 1983). Calcium. magnesium and sodium are the major cations. with potassium as a minor cons­ tituent. Bicarbonate and sulphate are the domi­ .,...... ,,'--- Basal till nant anions. Calcium. magnesium. sodium and bicarbonate constitut e mor e than 90% of the Fig. 7. (a) PoSItion of spr ing B in a hummoci

Springs 1000 ms-'. The saturated zone must be rather The marked spr ing horizon along the eastern thin with a flow parallel to the bedrock surface valley side is found at an altitude of 930 m.a. down towards the spr ing horizon. s.1. in the south . rising to about 1000 m in the The most typical springs are found in the north (Figs. 1. 3 & 4). More than 80 distinct follow ing positions: springs can be mapped over a distance of (i) Single springs downslope of meltwater three kilometres. with mor e diffu se seepage channels which act as confluence areas for faces between them. the gro undwate r (Spring A. Figs. 3 & 6). The seismic profile indicates that the perme­ (ii) Groups of spr ings inside topographical able sediments are mainly unsaturated (Fig. depressions downslope of greater accumulati­ 4b). with seismic velocities between 800 and ons of coarse sediments. The latter common- NGU - BULL. 422.1992 Groundwater contribution to a mountain stream channel 9

Sum of cations (" Eqv/I) tions in the springs are found at the end of 500 ,------~ winter (March-April) (Fig. 8) befo re the meltwa­ ter reaches the water table. Variations in con­ centration reflect degree of dilution and variati­ C ons in storage time for the groundwater. The similarities in groundwater level fluctuati­ 300 on and chemical composition indicate that all the springs are fed by the same type of aqui­ / -' .'.' . " fer, a shallow unconf ined aquifer in coarse 200 ~ \ : ;. . ~+- T V. , ~ <, • ,~ ~ -c.~ . Quaternary sediments. Since the sediments I ~ , -- -- ' _ _ • ...,...... 'A- ~ are rather inhomogeneous they probably form 100 . ' "\K!' !-- -. many local, limited aquifer units rather than •.- Ii • one single continuous aquifer along the valley side . Three springs, A, B, and C, have been stu­ died in more detail. Fig. 8. Cation content (ueqzl) of the springs during the years Spring A (Fig. 3) has a relatively low ion 1989-1991. Samples from all three years are plotted in the same diagram to show the general annual variation. Springs content (Figs. 5 & 8). Its upper, main outlet A, B and C are shown by curves. Small black squares are is active only when the groundwater level is samples from other springs in the catchment. high, i.e. from May to the middle of October (Figs. 6 & 9). The rest of the year only a diffu­ Iy form a distinct hummocky topography se seepage face is found some metres below (Spring B, Figs. 3 & 7). the main spring A outlet. The highest ground­ (iii) Single spring outlets in topographical water level is established one to two months positions some metres below springs of types after the snow melt. After the start of an inten­ (i) and (ii) (Spring C, Figs. 3 & 7b). sive rainy period during the summer it takes Between the marked spring outlets, a seepa­ at least two weeks before the discharge from ge face extending along the whole valley side spring A starts to increase (Fig. 10). feeds the downslope peatland areas with Spring B has a medium ion concentration water (Fig. 3). In dry summer periods no stre­ (Figs. 5 & 8). Its discharge is more stable than ams are found above the spring horizon. The that of spring A, but spring B also has its streams leading from the springs have a signi­ highest discharge in the middle of the summer. ficant discharge even after long dry summer Spring C has the highest ion content of all periods and also during the whole winter. the springs. The lowest values , found in the The ion concentration varies among the middle of the summer, are higher than the springs (Figs. 5 & 8), with the highest concen­ highest winter values for spr ings A and B trations for the springs topographically lowest (Figs. 5 & 8). The discharge from spring C is down in the valley side. The highest concentra- significant even in the late part of the winter.

SPRING A

Q) 4 2' jg 3 o cS 2

J FM A J FMAM JJ A SO ND 19 9 0

Fig. 9. Discharge of spring A(lis) in 1989 and 1990. 10 Sylvi ne taorsen,Jens-Otet Englund. Per Jerqensen, Lars A. Kirkhusmo & Dag Hongve NGU· BULL. 422. 1992

The change in chemistry along the stream I/ s flowin g from spring A to the Skvaldra is insigni­ 5 ficant during low discharge situations in sum­ mer , as well as during winter. The water samp­ Disch arge 4 led at the spring outl ets is therefore repr esenta­ tive of the groundwater that drains into the Skvaldra via the small streams leading from 3 the springs. The water supp ly to the Skvaldra from the springs thus has an annual variation with one ~ Eq vll ~cat ion s main maximum in discharge dur ing the sum­ 2001 mer. This is the same annual variation which is ob served for ot her aquifers in the inland 100j mountain areas of south Norway (Kirkhu smo '---r-::-,---.-,--.-----r--.~- & Sensterud 1988). 10 20 A u g u st

Groundwater in basal till 5 0 About 80% of the compact basal till, stretch ing fro m the spr ing horizon down to the Skva ldra , 4 0 E is covered by peat (Fig. 1). The till forms lo­ E cal unconf ined aquifers along the valley side c 30 where it is not covered by peat. Along the 0 rn valley bottom the peat forms a confining lay­ ... N '0. 20 er. Two groundwater tubewells are located in '0 an unconfined part of the comp act till in the c::'" lower part of the valley side (the two tube­ 10 wells to the right in Fig. 1). The lower one (NGU 15007) ext ends to a depth of 2.4 m below the ground surface and the upper (NGU 10 2 0 10 2 0 15008) to a depth of 5.1 m. The distance betwe­ J u ly Au g u sl en them is about 100 m. Falling head tests (method: Hvor slev 1951) Fig. 10. Variation in discha rge and cation content of spring gave hydraulic conductivities of 2 x 10-' ms-' A in Augusl 1988 in relation to prec ipitation in July and (tubewell 15007) and 5 x 10-' ms-' (tubewell August 1988. 15008), which are typ ical values for a com­ pact basal till (Lind & Lundin 1990), The till thu s has a limited ability to transport water Gr ound wate r levels in till down to the valley bottom. The annual ground ­ - 15006 ---- 15007 ·· ·· ·····,5008 water fluctuation in the two tubewe lls is about " '------.r-- 1.5 m, with the highest values occurring dur ing o - - -, .. .. I . .••••• . •. . ~ '~:" ." r~· '· ·~~~ ~·· ~~ ----- '.''''1 .. ./... the summe r. This is a typ ical pattern for , '. , -, .•..~ ... ":'':':':'.,: qrouncwatc in the mountainous regions of southeaste rn I, , rway (Kirkhusmo & Sensterud I 1988). I , ,ae , The contribution of water from the till to the " '" ~ I Skvaldra has been calculated in two differe nt I .~!\tV\ i'",,:,:,'.,J. /0"; way s: '~h , I (i) Lowering of the groundwater table. During ;:'i

the winter month s ther e is no recharge to the -a till, except for some water which may flow into the till from the permeable sediments of

the upp er area (Fig. 4b). There is no loss of Fig. 11. Fluctuations in groundwater level of tubswalts' water from the till by evapotransp iration. The 15006, 15007 and 15008. NGU · BULL. 422,1992 Groundwater contribution to a mounta in stream channel 11 lowering of the ground wate r level (Fig. 11) lar to many of the springs (Fig. 5). Water samp­ roughly corresponds, therefore, to the amount les taken from tubewell 15008 have a higher of water which has drained from the till to the ion concentration than those from tubewe ll bottom of the valley and later contributed to the 15007 because the for mer is placed deeper discha rge of the Skvaldra. From Dec.12th 1989 down in the till. Samples from the botto m of to Feb. 25th 1990 (75 days) the groundwater the peat betwee n the Skvaldra and tubewell level declined by 50 cm in bot h tubewells 15007 give values in the same range. It is 15007 and 15008. Based on other studies of thus not poss ible to distinguish between wate r basa l tills (e.g. Haldorsen et al. 1983) spec ific fro m the till and water from the springs by yield is estimated to abou t 10% and the length means of chemistry alone; of the till slope from the spring horizon down The till water has been samp led only in the to the Skvaldra is about 1 km. If the whole area between the Skvaldra and tubewell 15008 till area was an unconfined aquifer, the obser­ and only down to 5 metres depth. Till wate r ved lowering of the water table would corre­ from other parts of the area has not been spond to a release of wate r from the till to stud ied. However, since the basal till is very the Skvaldra of 8 x 10-3 m's-' per km'. Howe­ uniform, the obtained values are probably re­ ver , much of the till forms a confined aquifer, presentative for other parts of the till down to where the storativity is much less than the a depth of 5 metres. specific yield. A general lowering of the piezo­ metr ic surface by half a metre in the confined parts of the till aquifer would yield a much Groundwater with a long residence smalle r amount of water to the Skvaldra than time calcu lated for unconfined cond itions . Based In the middle of the valley bottom, close to on typical values of storativities for confined the river Skvaldra a groundwater tubewell in aquifers, the real flux from the who le till area till extends to a depth of 3.5 m below grou nd to the Skvaldra is probably not more than a level (NGU 15006, the tubewe ll to the left in tenth of the calculated value. Fig. 1). The cond itions are artes ian the who le (ii) Groundwater flow to Skvaldra. The year , with a press ure surface above ground groundwater grad ient betwee n the two tube­ level (Fig. 11). The ion concentration in water wells is 1:10 which is equal to the topographi­ from this tubewell is about ten times higher cal gradient. This is representative for the than that of most of the other studied ground­ who le till slope from the tubewell 15007 up water types (Fig. 5). The ion concentration has to the spring hori zon. The flow of groundwa­ only a small variation throughout the year. The ter is thought to be mainly one-dimens ional artes ian pressu re could be caused by the and directed down the valley slope . The hy­ unconfined aquifer in the uppe r part of the drau lic conductivity around tubewell 15007 at valley sides feed ing a confined aquifer lower 2 m depth was found to be 10-7 ms-'. The dow n. However, the high and rather stable ion hydraul ic conductivity nearer the till surface is concentration indicates that this is a deep obviously much higher due to the occurrence gro undwater, or a groundwater with a signifi­ of fractures and root channels, while the valu­ cantly long residence time , which discharges es deeper down probably are lower (as for in the centre of the valley , as has earlier been tubewell 15008). If the hydrauli c conductivity proposed for the main Asta catchment (Fig. value from tubewell 15007 is used, and the 1) (Englund & Haldorsen 1983, Englund 1986). average thickness of the till is estimated to The small variat ions in pressure head and be 10 m, Darcy 's law implies a water trans­ chemical composition indicate a nearly cons­ port of 10-' m's-' down to the Skvaldra per tant annual flux of this groundwater type . It km width of the area. is not clear if the water originates from the The whol e till slope area in Godlidalen is deepest part of the till or from the bedrock about 7 km'. If the calculation above is repre­ below it. sentative, it indicates that the Skvaldra recei­ Tubewell 15006 is the only locality where ves a till water component of between 6 x the deep groundwater has been sampled. Its 10-l and 7 x 10-' rn's: ' during the middle of representativeness for the catchment as a winter . whole has not been verifi ed. However, the Water samples fro m the two tubewells in bedrock is very homogeneous, as is the overly­ the till have ion conce ntrations which are sirni- ing till. The topographical grad ient of the val- 12 Sylvi Haldorsen , Jens-Olaf Englund, Per Jorgensen, Lars A. Kirkhusmo & Dag Hongve NGU · BULL. 422.1992 ley sides in the stud ied part of the catchment groundwater level in the till are low during the does not vary very much , and the gradient whole snowmelt period . The snowmelt flood of the valley bottom is very small. There is, is ther efore completely dom inated by direct therefore, no reason to suppose that the deep supp ly of melt water, as surface run-off or groundwater compone nt along the valley shallow channelled interflow , down to the should vary significantly. Strea mwate r samples Skva ldra. take n at several places along the Skvaldra in Marked precipitation events in moist periods August 1987 and 1988 showed very little varia­ give a rapid increase in the discharge of the tion in wate r chem istry (Bosch et al. 1988, Skvaldra . After a rainsto rm the discharge dec­ Anema et al. 1989) indicating a rather uniform reases very rapidly. The correspond ing delay distr ibution of the different water components in the increase in discharge from spring A, along the Skva ldra. which reacts quickly to rainstorms compared The influence of the deep gro undwater is with the other spr ings, was found to be about clear ly seen in the chemistry of the Skvaldra. two week s. During this groundwater delay In the winter the ion co ncentration in the period , the discha rge in the Skvaldra has typi­ Skva ldra's stream water is nor mally higher than cally nearly returned to baseflow conditions. in spring C (Fig. 5). There are no othe r sour­ This means, in the same way as argued for ces for such water other than the deep ground­ the snowmelt flood , that the groundwater supp­ water which discharges in the middle of the ly is of very little importance for the discharge valley. of the Skvaldra even during the latter parts of flood events . During a rainstorm, water di­ scharges as surfac e run-off or follows shallow channe ls in the peat or the soil down to the Peatland hydrology Skvaldra (Fig. 4b). The peat is very important The 40% of the Skvaldra catc hment which is since it constitut es most of the area along the cove red by peatlands (Figs. 1 & 3) plays an valley bottom. this is very apparent after hea­ important role in its hydrology. The hydraulic vy rain; the Skvaldra then becom es brow nish­ conductivity of the peat was measured at three coloured due to a high humic con tent in the localities between tubewe lls 15006 and 15007 water. The water soluble humic substances by falling or increasing head methods (Hvors­ sto red in the peat are partly washed out from lev 1951). For the upper part of the peat the it under such conditions . value varies betwee n 5 x 10-' and 3 x 10-' It is therefore concluded that groundwater rns", while below 50 cm depth the value drops flow does not significantly influence flood di­ to 1 - 2 x 10-< ms-I. In the deeper part of the scha rge in the Skvaldra dur ing any part of the peat the hydraulic conductivity is much lower year . than in the till. The peatlands clearly act , there ­ fore , as a confining layer overlying the till. The Baseflow and groundwater budget wate r transport through the deeper part of the It is difficult to say how much of the baseflow peat must be very slow, and therefore of little is real gro undwater and how much is surface import ance for the hydrological budge t of the water or shallow interflow wat er. In the Skvald­ Skvaldra . ra catchment, water from peatlands, as well as from the three small lakes, will certainly cont ribute to baseflow during dry periods . According to studi es by Yasuhara & Storm (1992) in Trondelaq (mid- orway) the flux from peatl ands is important for the baseflow of ri­ Hydrological budget vers, even when the watersheds are rather of the Skvaldra dry. However, from Octoberl November and dur ing the winter months, the surface water Flood events influence decreases and the baseflow beco­ In 1989 and 1990 the snowmelt flood occurred mes more and mor e dom inated by groundwa­ from April to May (Fig. 2). The conclusions ter. It is thus thou ght that the lowest dischar­ above indicate that the ground wate r compo­ ge values recorded during winter approach the nent of the snowmelt flood is insignificant, true groundwater basetlow value. since the discharge from the spr ings and the The January baseflow in the Skvaldra during NGU- BULL. 422, 1992 Groundwater contribution to a mountain stream channel 13 the winters of 1989 and 1990 was about 0.25 Table 1. Calculated compo nents (% ) of diffe rent groundwa­ m's- '. By the latter part of February it had ter types co ntibuting to Skvaldra dur ing win ter baseflow period s. Dat a from spring A gives minimum . and data from decreased to about 0.05 rn's'", In 1991 the spring C gives ma ximum . spring water components. minimum discharge was even lower and Feb­ ruary discharge values of 0.03 rn's: ' were PERCENTAGES OF DIFFERENT GROUND­ measured. To make a groundwate r budget for WATER BASEFLOW COMPONENTS these low baseflow situations , the following assumptions, whic h are based on the discussi­ CALCULATEDCOMPONENTS(%) ons above, have been made: Based on data from Spring Deep Till (i) The total baseflow is due to the three water groundwater water groundwater components described earlier in Feb.1991 SpringA 66 20 14 the paper , while the contribution from surface SpringC 76 10 14 water is insignificant. March 1990 Spring B 82 13 5 (ii) The deep groundwater sampled in tube­ March 1989 Spring A 70 20 10 well 15006 is representative for the whole Spring B 72 18 10 catchmen t. SpringC 79 11 10 (iii) The average groundwater component from the springs lies between the observed values for spring A and spring C, If the lower ion concentration found in spr ing (iv) The shallow till groundwater in the enti­ A is regarded as representative for the winter re area has an average composition close to spring flow, the same calculation gives a that of tubewells 15007 and 15008. The di­ spring water flux of 66%, a deep groundwater scharge from the till is not higher than 5 x flux of 20% and a till water component of 14%. 10-' m's- '. A similar calculation for early March 1990, (v) There exists.110 groundwater with a com­ using data from spring B, yields a spring flow pos ition betweenthat of sprinqC and tube­ component of about 82%, a deep groundwa­ well 15006, i.e. there is a real difference betwe­ ter flux of 13% and a till water component of en the deep groundwater component and the 5% (Table 1). For early March 1989 (Fig. 5) shallow groundwater, with no intermediate similar calculations give a spring component groundwater types. of 70, 72 and 79% and a deep component of Based on these assumptions one can make 20, 18 and 11%, using data from springs A, the following approximation of the groundwa­ Band C respectively. The till water compo­ ter budget for late February 1991. The cation nent is then calculated to be 10%. conce ntrations for spring C, tubewell 15006, It is concluded, therefore , that the contributi­ tubewell 15008 and the Skvaldra are applied on from springs is the most important compo ­ as input data. The relative water contribution nent of winter baseflow in the Skvaldra , com­ from the springs (X) and from deep groundwa­ prising cons iderably more than 50%. The deep fer (Y) are then calculated as follows: groundwater constitutes less than 20% of the tota l baseflow. The calculation of the flux from X • cation concentration spring C the basal till is based on a series of assumpti­ + Y • cation concen tration tubewell 15006 ons which are not verif ied by field data. Howe­ + Z • cation concentration tubewell 15008 ver, the till wate r chemistry is so close to the = cation concentration of the Skvaldra spring water chemistry that an error in the till water flux would mainly affect the calcula­ zrs the relative water contribution from the ted spring water component and would have till. The total discharge in Skvaldra in late little effect on the calculated deep groundwa­ February is 3.6 x 10-' rn's" . Thus, ter flux. The calculation of the maximum deep Z = 5 X 10-'/ 3.6 x 10-' = 0.14 (i.e. 14%). groundwater flux is thus regarded as a rather The second equation required to solve this good estimate . proble m is, It was difficult to separate the baseflow X + Y + Z = 1 (total discharge is 100%). part of the limnigrammes during the summer The calculation yields a spring water compo­ periods , because rain events were frequent nent of 76%, a deep groundwater component during most of the observed summers. In of about 10% and a till water component of addition the groundwater discharge responds 14% of the tota l baseflow (Table 1). very slowly to rain events, with a delay of at 14 Sy/vi Ha/dorsen, Jens-o tet Eng/und, Per Jerqensen, Lars A. Kirkhusmo & Dag Hongve GU- BULl. 422 . 1992

least two weeks. Compared with the winter, Englund. J-O. 1986: Spring cnarac ero s ICS and hydrolog ical a calculation of the different groundwater com­ rnoce rs of catchments. ora .Hyorot. 17. 1-20. ponents is comp licated to carry out. Howe­ Englund J-O . & Halc orsen, S. 1983: T e As tada len catch­ ment. southeaste rn orw ay. geo log y and general voro­ ver, this study does support the following logy. Rep.Dept. of Geol.Agric.UnlV. of orwa y 18.42 pp. deductions. Germann. P.F. 1986: Rapid dr ainage response 0 orecipi a i­ During the summer the total deep groundwa­ on. Hydrol. Processes 7. 3-13 . ter flux and till water component are probably Haldorsen . S. 1982: The genesis of tills from Astadalen. southeastern or way. Nor.Geot.t tassi«. 62. 17-38 . about the same as in the winter. The spring Hatcors en. S. 1983: Miner alogy and geochem istr y of basa l discharges are at a maximum in t:,e middle till and their relationship to \Ill-formin g processes. or. of the summer and early fall. The total ground­ Geol.t iosskr. 63. 15·25 . water flux is therefore expected to be higher Halcor sen. S.. Jenss en. P.D.. Kc nter. J .Chr . & yhr. E. 1983: Some hydraulic properties of sanov-suiv or- in summer than in winter. The ion content of wegian nns. Acta Geol.Hisp. 78. 191-198. the Skvaldra baseflow is lower during summer Hewlet t, J.D. 1982: Prmclples of forest hydrology. The than during winter because all the springs Un iv, of Georg ia Pres s. Athens. Geo rgia. U.S.A.. 183 pp . have lower ion contents in summer than win­ Hvorstev, .J. 1951: Time lag and soil permea bili y In ground water observauons, u. S. Army Corps of Engm. ter (Fig. 5). Waterways Expenment.Stat.Bul/. 36. 50 pp . The mean annual groundwater flux to the Hlllestad . G. 1990: Seisrmske rnaunqer i Astadalen. or. Skvaldra must be more than 0.03 rn's" , equiva­ qeot.unaers. Report 90.036. 5 pp . lent to at least 10% of the annual precipitati­ Horton. R.E. 1933: The role of infiltration in the hydrologiC cycle . Ann.Geophys.Umon Trans. 14. 446- 460. on. Of this. most is recharged above the Kennedy. V.C.. Kendall. C.. Zellweger. GW.. Wyerman. TA spring horizon. while precipitation along the & Avanzmo, R.J. 1986: Determina Ion of he compo­ lower part of the catchment mainly contributes nents of 5 orm flow uSing water chemist ry and en " on­ to the flood events. ment al ISOtOPeos. auore River Basin, Cahtornia. J. Hydr. 84. 197- 140. K" by..J. 1978: Htllslope hydrology. Joh n oI ey &Sons. Ackno wledge ments ew York . 386 pp . K" husmo . L. & Sonst erud. R. 988: Over vakrunq av grunn­ Financial support was pro vided from the orweq ian auo­ vann . or.qeot.uncers. Report 88.046. 15 pp. nal Committee of Hydr olog y. Glaamen & Laage n Brugseier­ Koh ler . J.Chr. 1985: Kvaruergeologisk kart - Goauoeten fore ning and the Norwegian Water Resources and Energy 7:70 000 . LVF's inst. for geore ssurs- og foru rensnings­ Adm inistration were responsible for the discharge stat ion . Iorskninq (GEFO). As. Norw ay. The orweg ian Meteorolog ical Inst itute has been responsib­ UndoB.B. & t.und m, L. 1990: Saturated hydr aulic con duc ti­ le for the preci pitatio n data . Facilities have been placed at vity of Scandinavian tills . ora.nyor. 2t. 107-118. our dispo sal by Plhlske Skogsameie. B.v.dWeerd. D.J .G. Parso ns . D.J .. Stohlgre n. T.J. & Graber. D. . 1986: Long ota and R.v.d.Berg from the Inst itute of Soil Science and Geolog y. Univ, of Wagen ingen supervised two groups of term effe cts of acid depos ition on selected ecos ystems Dutch students in the field. Valuab le comments and co ns­ of Sequia anonal Park. Californ ia. U.S. Dept. Interior. truc tive cnnc ism have been given by D. Banks. H. Hueslat­ at. Park Service. Ann. Rep.. Dec. 1986. Three RIvers . ten. G. Storro and an anonymous refe ree . G. Blocn. L. California. Jakobse n, B. Sonsteby and R. Sonsterud assisted In the Peters. .E. & Murdocn, P.S. 1985: Hydrologic co mparison field. A. Borga n and B. Hop land drafted most of the figu­ of an acidic- lake basin With neutral-lake bas in in the res . To these person s and institutions we render ou r since­ west central Aoiro ndack Mountains . ew York. Water. re thanks. Air & So" Pol/ut. 26. 387-402 . Pinder, G.F. & Jones. J .F. 1969: Oeterrmna uon of the gr ound­ wa ter com ponent of peak disc harqe from the Chem istry of total runoff. Wat.Res.Res. 5. 438-445. References Siedlecka . A.. ystu en. JP .. Englund . J.O. & Hossack. J. 1987: Ulleha mmer - berggrunnskart M. 1:250000. Nor. Anema . D.. Jansse n. R.. [ ssen, B. & Veenis. N. 1989: A qeot.unders . hydrogeologlc al reconnaissance of the Skvaldra catch­ Sktasn, .G.. Stewar . .K. & Pearce . A.J. 1986: S orrn ment . Southeaste rn orway. Agricultural University of runo f generation In nurmo neacwater catchm en 5 2. A orway - u rnversuy of Wage ninge n. 113 pp . case study of rutlstope and loworder strea m respon se. Baron. J. & Bricke r. O.P. 1987: Hydrolog ic and chemical Wat.Res.Res. 22. 1273 -1282. fl u x In L OCh Vale watershed. R OCk y Mountain ano n a r 'Vlnter. T.C. 19 8 6 : E ffe ct of groundw3 e r recharge and Park. In: Averett . R.C. & cK night. D.M.(eds.). Chemi­ con Igura Ion of he water able benea h sand dunes cal quality of water and the hydrologic cycte. t.ewis and on seepa ge in lakes In the Sand Hills of eo ras ­ Publishers. Chelsea . L a. USA. J.Hydr. 86. 221 -237. Boscn, R.v.d.. Eggln . H.. Pelgrum. R. & Vermaas. J. 1988: Yasuh ara .. & Storro , G. 1992: Base flow procuc ion rorn A hydrogeologlcal reconnaissance of the sk vstar« catch­ paruatly peat-cov ered wa ter s ecs : A case study in rmdd­ ment. Southeast Norway. Agricultural Univers ity of le orw ay. or.geol.unaers. 422.(this volum e). orway - Univers ity of Wage mngen . 84 pp. Englund . J-O. 1983: Che mistr y and flow pattern in some groundwate rs of Southeastern orway. or.geol Manuscript received October 1991: revised uruiers. 380. 221-234 . typescrip t accepted February 1992.