Oceanological and Hydrobiological Studies International Journal of Oceanography and Hydrobiology Vol

Oceanological and Hydrobiological Studies International Journal of Oceanography and Hydrobiology Vol. XXXVI, No. 1 Institute of Oceanography (103-124) University of Gdańsk ISSN 1730-413X 2007 eISSN 1897-3191

DOI 10.2478/v10009-007-0012-7 Received: July 1, 2006 Original research paper Accepted: February 29, 2007

The transport and distribution of the river load from the Reda River into the Puck Lagoon (southern Baltic Sea, Poland)

Ewa Szymczak1, Halina Piekarek-Jankowska

Institute of Oceanography, University of Gdansk Al. Marszałka Piłsudskiego 46, 81-378 Gdynia, Poland

Key word: river sediment transport, Reda River, Puck Lagoon, Baltic Sea

Abstract

The main aim of this study was to determine the size of the load carried by the Reda River that was discharged into the sea and the load distribution on the bottom of the Puck Lagoon. Water exchange with the open sea was limited in this shallow reservoir where the average depth was 3.13 m. The input of material was dominated by river transport, whereas abrasion and aeolian processes were insignificant in the total sediment inflow. The Reda River, one of the main rivers flowing into the lagoon, is 44.9 km long and has a catchment area of 485.2 km2. The investigations were conducted between 2001 and 2004 at the Mrzezino hydrological cross-section and at the river mouth in the Puck Lagoon. The study demonstrated that the Reda River discharged annually approximately 9,900 tons of sediments into the Puck Lagoon, 73% of which was the bed load that in the final course of the river created an underwater accumulation form. The granulometric composition of the deltaic deposits, similar to the bed load, was dominated by coarse-grained sand fractions. The proportion of the aleurolite and pelite fraction was insignificant at less than 1%. The suspended sediment was composed of particles that ranged in size from 0.00045 mm to 0.25 m. Mineral particles were more common than organic ones in the load discharged by the Reda River into the Puck Lagoon and constituted 99% of the bed load.

1 Corresponding author: [email protected]

104 E. Szymczak, H. Piekarek-Jankowska

INTRODUCTION

The discharge of basin waters and mineral and organic material resulting from basin denudation and river channel erosion is the main function of rivers. The scale of the erosion processes in the basin depends on the climate, surface features, geological structure, plant cover, and human activities. Rivers can transport dissolved load and particulate matter as suspended sediment load or as bed load. The manner of transport of the particulate matter depends on the interrelation between the flow velocity in the river channel and the size and weight of the particles. The particles can be transported on the river bed or as suspensions in the water mass. The boundary diameter of particles that differentiate the suspended sediment load from the bed load is not a fixed value. The size of particles transported in the suspension changes depending on the flow velocity and ranges from fine clays to pebbles, although it can also, although rarely, include particles larger than coarse-grained sand (>0.5 mm). Normally, the suspended sediment load is dominated by the silt and clay fraction with grain diameters of less than 0.063 mm, which in many rivers of the world constitutes from 50 to 100% of the load composition (Ongley 1996). Research on the river load transport in the mouth stretches of both the largest river systems (Jaeger and Nittrouer 1995, Chen et al. 1999, Milliman et al. 1999, Li et al. 2001, Woodruff et al. 2001, Islam et al. 2002) and smaller rivers indicates that the inflow of such loads play a considerable role in sedimentation processes (Milliman and Syvitsky 1992, Ferster and FitzGerald 1996, Patchineelam et al. 1999, Sottolichio and Casting 1999, Lopes et al. 2001, Milliman 2001, Serrat et al. 2001). These types of investigations also aim at determining the global inflow of terrigenic material that rivers discharge into the seas and oceans. In Poland, river load research dates back to 1923 (Born 1928). The first scientific work conducted by the hydrological services concerned the movement and quantity of the suspended sediment load and the bed load in the Vistula River. Large-scale research into the river load was begun in the 1950s and continued until the early 1980s (Dębski 1957, Brański 1968, Pasternak and Cyberski 1973, Skibiński 1976). On the Polish coast research into the quantity of load transported by rivers was conducted in 1955-1965 by Brański (1968) and in 1978-1980 by Cyberski (1980, 1984) and Dynus-Angiel (1983). This research was devoted to the largest rivers of the Baltic Coast - the Rega, Parsęta, Wieprza, Słupia, Łupawa, and Łeba - which run directly into the Baltic Sea. The general hydrological conditions of the Puck Bay catchment area were presented in studies by Cyberski and Jankowska (1984), Friedrich (1984), and Cyberski (1993). However, the question of river load transport and the quantity

The transport and distribution of the river load from the Reda River 105 of its discharge to the sea was not addressed. Data on the quantity of the total suspended sediment in the waters of the River can only be found in the regular publications of the Institute of Meteorology and Water Management in Gdynia (Environmental Conditions in the Polish Zone of the Southern Baltic) and the Environmental Protection Inspectorate in Gdansk (The Cleanliness of Rivers, Lakes, and the Baltic Sea). Of the issues pertaining to the course of river-related processes in the Puck Bay catchment area, the river load transport has been relatively little studied. No studies have addressed the dispersal of the sediment material discharged by the rivers to the sea nor how this material sediments. The aim of the present study was to determine the quantity and seasonal change of the discharge of sediment material transported by the River to the Puck Lagoon and to determine the rules regarding the dispersion of the material in the water column and on the reservoir bed. The study focuses on the particulate fraction transported in the suspension and in the bed load.

MATERIALS AND METHODS

The determination of the quantity of the suspended sediment load and the bed load in the Reda River was based on the results of stream gauging and measurements of water turbidity as well as results of grain size analyses of channel deposits. Field work was conducted at the measuring station at Mrzezino from November 2001 until October 2003 and in February and May 2004. The measuring station was located at a distance of 2.6 km from the mouth in a cross-section closing 99.5% of the basin area. Water samples and bed deposits were collected in the vicinity of the Reda River mouth in June 2004 (Fig. 1). The multipoint measurements of the turbidity field were accompanied by stream gauging, which permitted determining precisely the suspended sediment volume. The measurements of flow velocity and quantity were carried out on a monthly basis in determined hydrometric columns using a 2030R Eijkelkamp mechanical current meter in compliance with the guidelines in Pasławski (1973) and Bajkiewicz-Grabowska et al. (1993). Water samples of 1 dm3 were collected in three bathometric columns identical to the hydrometric columns (one in the current zone, two off the current zone) at three depths - near the surface, at mid column depth, and by the bed. Deposit samples were collected from the river channel (in the current zone and at a distance of one-sixth of the channel breadth from the right and left river banks) three times throughout the research season for the purpose of determining bed load discharge.

www.oandhs.org

106 E. Szymczak, H. Piekarek-Jankowska

Fig. 1. Location of the research station and sample collection points.

Laboratory analyses included: • determining the concentration of particulate matter in the river and sea water and the share of the organic and mineral fractions in the water; • determining the grain size composition of the suspension, the river bed load, and the bed deposits located on the bed of the Puck Lagoon by the mouth of the Reda River. In order to determine the concentration of the suspension, samples of river and sea water were filtered through GF/F Whatman glass fiber filters (pore diameter 0.7 μm, effective filtration 0.45 µm). The filters were then annealed at 450ºC. The quantity of mineral and organic suspension was determined based on the difference in their weight before and after the annealing. The mineral composition of suspensions and deposits was determined at the Polish Geological Institute in Gdansk with the help of an ANALYSETTE 22 laser particle size (fraction <0.063 mm) and sieve analysis in which sieves with mesh diameters of 4.0, 2.0, 1.0, 0.5, 0.125 and 0.063 mm were used. The statistical analysis of particle size distributions was based on moments analysis performed with the Gradistat program. The average velocity in the columns was calculated based on point measurements of water flow velocity in hydrometric columns. Geometric measurements of the river channel and water flow velocity were used to calculate the cross-section area, the volume of water flow per time unit (Q), and

The transport and distribution of the river load from the Reda River 107 the average velocity (Przepływ software was used for this purpose). The results of the particular flow velocity measurements were compared with the mean monthly and annual flow values for the Wejherowo station in 1971–2002. Using the available turbidity and streamflow figures, sediment volume was measured for each measurement cycle (Pasławski 1973, Bajkiewicz-Grabowska et al. 1993):

−3 U i =10 PiQi (1)

–1 where: Ui is the sediment volume in a given measurement cycle [kg s ], Pi is the –3 turbidity value resulting from a given measurement [g m ], Qi is the flow velocity resulting from the measurement [m3 s–1].

The annual mass of suspended sediment load transported was calculated based on (Ozga-Zielińska and Brzeziński 1994):

R = 31,5576PsQs (2)

where: R is the mean annual transport of suspended sediment load [t], Ps is the –3 3 –1 average turbidity [g m ], Qs is the average annual flow [m s ]; the number coefficient results from the conversion of units.

The quantity of the bed load was calculated based on formula (3) proposed by Skibiński (1976):

−2 0,1343 0,4687 1,2080 qr =10 2,26vd hCd Re Fr (3)

2 –1 –1 where: qr is a unit of volume discharge of the bed load transport [m s m ], vd is the dynamic velocity [m s–1], h is the column depth [m], Fr is the Froude number, Re is the Reynolds number, Cd is the feature of domination characterizing the changeability of load grain size.

3 –1 To determine the intensity of transport of the bed load Gr [m s ] in the entire cross-section of the river channel, the following formula was used:

N g + g G = r,i−1 r,i Δb (4) r Σ i i=2 2

where: Δbi is the distance between columns, in which the unit bed load discharge equaled gr,, i – 1 and gr ,i, N is the number of columns adopted in the cross-section of the channel.

The conversion from units of volume to units of weight was based on the following formula:

www.oandhs.org

108 E. Szymczak, H. Piekarek-Jankowska

Grw = γ oGro (5)

3 –1 where: Gro is the bed load discharge volume [m s ], Grw is the bed load discharge -1 –3 weight [t s ], γo is the volume weight of the dry bed load [t m ].

The following formula was used to calculate the annual mass of the bed load transport:

M = 86400tGr,śr (6)

where: M is the mass [t] or volume [m3] of the transported bed load, t is the number –1 3 –1 of days in a year, Gr, śr is the average bed load transport discharge [t s or m s ].

STUDY AREA

The basin of the Reda River lies in three geographical mesoregions comprised of the marginal stream valley of the Reda and Łeba rivers, the Kashubian Lake District, and the Kashubian Coast (Kondracki 1991). The river sources are located west of the village of Strzebielino at 49.4 m above sea level in the marginal stream valley of the Reda and Łeba rivers, which, in this particular stretch, is 3 km wide. A part of the marginal stream valley stretches to the east, to the town of Reda. It is here that the Reda River enters the Kashubian Coast and flows on down the northern part of the Kashubian Meander, which opens towards the Puck Bay for 6 km. Beyond the town of Reda the river channel bifurcates towards the east. Its northern arm is the stretch of the Reda River mouth proper that discharges water into the Puck Lagoon (an internal part of the Puck Bay). The breadth of the Reda channel ranges from 0.4 m in the source stretch of the river to 15 m by the mouth; therefore, the river flows in a disproportionally large marginal stream valley. The morphology of the surface features in the basin area is highly diversified. For example, there are some undulating ground morainic plateaus comprised of mixed sand, gravel, and clay divided by fragments of marginal stream valleys to depths of 50–100 m. The pattern of the marginal stream valleys reflects the history of the late-Pleistocene drainage system that developed on the nearest forefield of the Scandinavian ice-sheet leaving the Pomeranian stage (Augustowski 1974). The dense river system of the Reda River, which is marked by basin asymmetry in favor of the right and, in contrast to other coastal rivers, has a parallel flow direction, developed on such a substratum bed. As the river valley is water-logged and peated, the Reda River drains strongly along the majority of its course; downstream, the river channel is regulated, while the mouth and its surroundings are natural.

The transport and distribution of the river load from the Reda River 109

The Reda River is 44.9 km long and its average fall is 0.98‰. The basin covers 485.2 km2, which is as much as 53% of the total catchment area of the Puck Bay. The hydrological regime of the rivers in the Reda catchment is shaped by relatively high rainfall, the domination of permeable and semi- permeable deposits, the presence of numerous valleys, and considerable differences in relative heights. In the mouth stretch of the Reda River, the quantity and direction of flow are influenced by the condition of the water in the Puck Bay (the presence of backwater). The Reda, similarly to other Pomeranian rivers, is marked by the snow and rain oceanic regime, which is manifested by increased water supply, higher water levels, and flow throughout the winter season (October to April). As a result, there are two characteristic supply periods: fall-winter (rainfall and snowfall) and January-April (melting snow). The lowest water levels are recorded in summer due to the high retentiveness of the substratum bed and increased evaporation. Due to the considerable share of groundwater in the supply of water to the rivers of the Reda basin (Piekarek-Jankowska 1994) as well as the relatively uniform supply from precipitation and considerable retention in the lakes and hollows without drainage, the streamflows of the Reda River are marked by little changeability. In its source stretch, the Reda River is also supplied with water infiltrating from the Łeba River. Further on, the river flows down the bottom of the marginal stream valley, which is the base of the regional drainage of groundwater from Quaternary, Palaeogene, Neopalaeogene, and Cretaceous deposits (Cyberski and Jankowska 1984). As a result, the Reda is a draining river throughout most of its course, and may only periodically change to infiltrating and supplying groundwater when the water level is high or during snow-melt floods. The Reda catchment area is located in the zone in which the impact of the Baltic Sea comes in contact with the lake district climate resulting in the spatial changeability of climatic conditions in the region. Precipitation is the most important element of the climate that influences the development of water conditions. Since the area under study remains under the influence of marine continental precipitation, there are little changes in precipitation throughout the year. The area’s topographic features and its exposure to westerly rain-bearing winds have a considerable impact on the quantity of precipitation. The highest annual precipitation occurred in the summers of 1951–1981 (May-October), and peak values were reached in August. The average annual precipitation totals are non-uniform. The largest amounts of precipitation were recorded on the plateaus and both sides of the Reda River marginal stream valley (600–700 mm). In the western part of the catchment area they are more than 700 mm. In the mouth stretch of the river and in the coastal sea zone (both regions are located in the rain shadow of the Kashubian Lake District plateaus),

www.oandhs.org

110 E. Szymczak, H. Piekarek-Jankowska precipitation levels are the lowest and do not exceed 600 mm annually (Cyberski and Szefler 1993). In the 2001–2004 period when the research into the discharge of the load carried by the Reda River to the Puck Lagoon was conducted, precipitation levels were 10-15% higher than they had been in 1951- 1981. During the research period, the annual precipitation pattern was dominated by liquid precipitation (approximately 85%), and snowfalls were recorded from October to May. Snow cover was first recorded in the lake district (at the end of November), then in the central part of the basin (end of November) and finally in the coastal area (at the beginning of December). The length of the snow cover period is also varied; it is the longest in the lake district area (80–90 days) and the shortest by the Puck Bay (50–60 days). The average annual temperature in the Reda River catchment area ranges from 6.5 to 7.5ºC. It is slightly higher in the coastal area than in the areas located further inland, which is evidence of the reductional impact the Puck Bay has on air temperature. The annual amplitude of temperatures, expressed as the difference between the mean temperatures of the hottest and coldest months, is also lower in the coastal area at 17ºC, while in the southern part of the catchment area (Michalska 2004). The Reda River basin is 40% forested (197.5 km2), with the domination of mixed (coniferous and deciduous) forest complexes. There marginal stream valley also contains agricultural areas comprised mainly of meadows and pastures. The Puck Lagoon is the most peripheral, western part of the Gdansk Bay and covers 103 km2, which is just 1.9% of the Gdansk Bay area. The average depth of this aquatic region is 3.13 m. The mean salinity of lagoon waters is 7.3 PSU, which results from the exchange of water with the Gdansk Bay and the inflow of rivers. Normally, the impact of river waters is limited to the area by the river mouths. This is also the case for the Reda River, the largest in the catchment area. After they are discharged into the lagoon, these waters flow south along the shore and finally reach the Gdansk Bay (Nowacki 1993). The Puck Lagoon has diversified bed features (Fig. 1). The patterns of shallows, channels, and hollows divide the area into two basins - the Puck Basin and the Kuźnicki Basin (Nowacki 1976). The Puck Basin spreads along the western coast and resembles a channel limited with 3 and 4 m isobaths, with the deepest spot at the Rzucewska Deep (5.7 m). The Kuźnice Basin, which spreads along the Hel Peninsula, contains two distinct hollows – the Kuźnicka Deep (9.7 m) and the Chałupska Deep. The exchange of waters between the two basins is hampered by the shallows of Virgin Sands that spread from the northwest towards the southeast from the Hel Peninsula as far as Seagull Shallow (Nowacki 1993). The lagoon shore includes mouths of marginal stream

The transport and distribution of the river load from the Reda River 111 valleys and the postglacial plateau on which cliffs have developed. Both the marginal stream valleys and the clays of the postglacial plateaus continue on the bed of the Puck Lagoon (Piekarek-Jankowska 1994, Słomianko 1974).

RESULTS AND DISCUSSION

In the period under analysis, the mean annual flow at the Mrzezino measuring station was 6.1 m3 s–1 (Fig. 2). The highest streamflow volume figures were recorded in January 2002 at 11.8 m3 s–1 and in February 2004 at 12.5 m3 s–1. The lowest streamflows (3.9-5.5 m3 s–1) were recorded in the summer months from June to August. The characteristic changeability of streamflows depends on river supply. In the analyzed measuring cycles the maximum streamflows resulted from the warming and the subsequent rapid melting of snow cover. This phenomenon was recorded in the third decade of January 2001 when mean daily temperatures were above 0ºC (with a maximum of 6ºC) and in the first decade of February 2004 when air temperatures were above zero.

Fig. 2. Reda River streamflow quantities (Q) at Mrzezino station.

Summer low flows resulted from increased evaporation in the catchment area that exceeded the precipitation level and the considerable retentiveness of the substratum bed. In 2002 and 2003, August was marked by low precipitation levels and the highest mean monthly temperatures annually. The mean discharge levels measured for particular months were compared with the analogical values from the Wejherowo measurement profile where

www.oandhs.org

112 E. Szymczak, H. Piekarek-Jankowska hydrological measurements have been conducted for many years. Stream gauging values were recalculated taking into account the increase in catchment area ratio from the Wejherowo station to the Mrzezino outfall. With the exception of those for January and September (Table 1), the results obtained fell within error limits and therefore can serve as a basis for drawing conclusions concerning the course of hydrological phenomena.

Table 1

Average monthly values of streamflow for the Reda River Average monthly values of Average measured monthly a Standard b Month streamflow values of streamflow deviation Q [m3 s-1] Q [m3 s-1] XI 6.83 2.76 5.84 XII 6.50 1.69 6.26 I 6.52 1.98 9.04 II 6.33 2.18 8.32 III 7.02 2.08 7.60 IV 6.08 1.73 5.44 V 4.61 0.92 5.02 VI 3.98 0.57 4.47 VII 4.33 1.77 5.14 VIII 3.89 0.82 4.00 IX 4.52 0.84 6.03 X 5.27 1.37 5.75 a – periods of time 1971 – 1983, 1994 – 1996, 2000 b – period of time 2001 -2004

The results of flow velocity measurements indicated that in the 2001-2004 period the Reda River discharged 0.193 km3 of fresh water to the Puck Lagoon annually, which constituted more than 76% of all the river waters flowing into the lagoon. The other rivers discharging waters to the Puck Lagoon, i.e. Kanał Łyski, Gizdepka, and Płutnica (Fig. 1) and for which measurements were taken simultaneously, discharged 0.06 km3 of fresh water in the same period. Calculations of the characteristics of the suspended sediment load were based on the measurement of streamflow volume and turbidity, i.e. the quantity of suspension per unit of river volume. The average turbidity of the Reda River during the period investigated was 13.56 g m–3, while the range was considerable at 6.02 to 88.06 g m–3 (Fig. 3). Variations in suspended sediment load, and therefore turbidity, resulted from the availability of sediments from the catchment area, which depended on the seasonal changeability of plant cover, precipitation intensity, snow cover, and basin denudation levels. The largest amounts of sediments were carried

The transport and distribution of the river load from the Reda River 113

Fig. 3. Turbidity (P) of Reda River water at Mrzezino station. during high water stages, which were recorded in periods of increased catchment area erosion that resulted from the melting of snow. Intense precipitation also activated the supply of sediment material from the catchment area; as precipitation continues, turbidity levels decrease (Allen 2000). During intense summer rainfalls, a marked increase in the turbidity of Reda River water was recorded. However, the streamflow volume did not increase simultaneously due to the existing hydrological conditions resulting from the geological structure. The correlation of the turbidity value and streamflow was r=0.14 on average because the parameters were not linearly dependent (Fig. 4).

Fig. 4. Relation between turbidity (P) and streamflow (Q) in the Reda River.

www.oandhs.org

114 E. Szymczak, H. Piekarek-Jankowska

During the investigated period, the average daily transport of suspended sediment load was approximately 9.2 tons; this value ranged from 1.4 tons/day (November 22, 2002) to 95 tons/day (February 6, 2004). The largest mass of suspended sediment load transported was correlated with either the highest streamflow or turbidity. Over the course of the measurements and subsequent calculations it was determined that the suspended sediment load discharged by the Reda River into the Puck Lagoon is 2,618 tons annually. The maximum inflow of the suspended sediment load transported by Reda and the other, smaller rivers of the catchment area was noted in February (37.8%) while the minimum was in October (2.97%). For the Baltic Sea the maximum annual inflow of suspended sediment load was recorded in April (22.2%) and the minimum in January (3.7%) (Lajczak and Jansson 1993). The structure of the suspended sediment load was dominated by the mineral fraction, which was 59% on average (Fig. 5). Its share in the particular samples taken throughout the year ranged from 39 to 85%. The domination of the mineral fraction over the organic fraction was the most apparent in the summer months.

Fig. 5. Share of organic and mineral matter in the structure of the suspended sediment and the bed load.

Analyses of the grain sizes of the suspended sediment load indicated the domination of silt and clay fractions, which together constituted more than 91% (Table 2). The 0.01 – 0.05 mm fraction constituted over 60% of the mass of the sediment transported. Fine-grained sand was the largest fraction (8% approximate share). The share of clay, the finest fraction, was 6.7%.

The transport and distribution of the river load from the Reda River 115

Table 2

Percentage share of particular fractions in the structure of the suspended sediment load Fraction

Clay Silt Sand <0.001 0.001-0.002 0.002-0.005 0.005-0.01 0.01-0.05 0.05-0.1 >0.1 [mm] [mm] [mm] [mm] [mm] [mm] [mm]

2.8 % 3.9 % 9.3 % 14.9 % 60.8 % 5.0 % 3.3 %

In larger rivers, such as the Vistula, silt and clay have a smaller share in the development of the suspended sediment load, and they normally jointly constitute approximately 70% (Cyberski 1982). The content of the silt and clay fraction transported in the suspension is not smaller in mountain rivers than it is in the River Reda either (Pasternak and Cyberski 1973). Many conclusions on the transport of the bed load in the Reda channel can be drawn from the changing shape of the river channel (Fig. 6) and the flow velocity in the river bed, which, during the measurements, ranged from 0.088 m s–1 (July 2002) to 0.927 m s–1 (January 2002). The mean flow velocity in the

Fig. 6. Changes in the shape of the river channel at Mrzezino station for selected measuring cycles.

www.oandhs.org

116 E. Szymczak, H. Piekarek-Jankowska river bed was 0.54 m s–1, while the average water flow velocity in the entire cross-section of the river channel was 0.58 m s–1. A flow velocity of >0.5 m s–1 allows the load to be transported on the bed (Gradziński et al. 1986); this is also facilitated by the absence of vegetation. In order to determine the bed load discharge and the quantity in the mouth stretch of the Reda River, it was necessary to analyze the grain sizes of the sediments deposited on the bed (Table 3). Table 3

Grain sizes in the sediments in the Reda River channel

Location Statistical grain size parameters Date of of sampling sampling point Mean Sorting (σø) Skewness (Skø) Kurtosis (Kø)

L -0.029 0.686 -0.079 3.429 X 2002 C -0.534 0.999 -0.261 2.481 R 0.030 0.864 -1.055 4.639 L -0.358 1.039 -0.646 2.906

Reda - Mrzezino IV 2003 C -0.169 1.065 -0.788 3.170 R -0.303 1.136 -0.406 2.481 L 0.302 0.567 -0.483 5.838 V 2004 C -0.172 0.826 -0.565 3.622 R 0.144 0.988 -1.045 4.793 L – left bank, C – current zone, P – right bank Mean: 1 ÷ 0 – coarse sand, 0 ÷ -1 – very coarse sand Sorting: 0.5 ÷ 0.7 – moderately well sorted, 0.7 ÷ 1.0 – moderately sorted, 1.0 ÷ 2.0 – poorly sorted Skewness: 0.43 ÷ -0.43 – symmetrical, -0.43 ÷ -1.3 – coarse skewed Kurtosis: 1.7 ÷ 2.55 – platykurtic, 2.55 ÷ 3.7 – mesokurtic, 3.7 ÷ 7.4 – very leptokurtic

The channel bed in the mouth stretch was comprised of coarse-grained sand. The bed material did not change much in the cross-section. The sediments collected off the current zone were sorted slightly worse, and there was a simultaneous increase in the share of the coarser fraction of gravel. This resulted from the smaller water flow velocity, which caused the deposition of coarser grains. The negative values of the skewness indicator also demonstrated that the material was enriched with coarser fractions and that the finer fractions, which were both transported in the suspension and on the bed, were eliminated from it. Kurtosis ranged from 2.4 to 5.8 phi, which indicated that the dynamic conditions prevailing in the environment were more or less uniform. The share of the organic fraction in the channel sediments was low and ranged from 0.1% to 2.3 % (Fig. 5). During the measurement period, the bed-load discharge and bed load quantity were calculated based on results of grain size distribution analysis using Skibiński’s formula. The results of these calculations indicated that the

The transport and distribution of the river load from the Reda River 117 majority of bed load was transported in the cross-section in the form of a bed load ribbon, the location of which changed depending on the streamflow conditions and bed sediment supply. Changes in the bed shape in the cross- section indicated that the bed load was transported along the entire breadth of the channel (this was also assumed in the calculations). The results of the calculations indicated that the Reda River transported from approximately 108 to 203 cm3 of sediment per second, which corresponded to 3,409–6,391 m3 (or 5,455–12,939 tons) annually. The units of volume were converted to units of weight based on the assumption that the weight by volume of the dry bed load was 1.6 g cm–3. Bed load discharge was strongly correlated with streamflow volume r = 0.9 (Fig. 7).

Fig. 7. Relation between the bed load discharge along the bottom breadth unit (q) and the streamflow (Q) in the Reda River.

Of the material discharged by the Reda River into the Puck Lagoon, 26.5% of the transported load (approximately 2,600 tons) was comprised of suspended sediments. Although this was lower than the quantity for other Pomeranian rivers which run into the Baltic Sea (Szymczak 2002), it must be remembered that the annual streamflows of the rivers (7.8 – 26.5 m3 s–1) were larger than in the Reda. The percentage share of the suspended sediment load in the total load mass was similar to the other rivers of Pomerania, in particular the Łeba and Rega (Cyberski 1984, Szymczak 2002). The figures for bed load, that ranged from 3,409 to 6,391 m3 (5,455–12,939 tons), were similar to the lower limit values calculated for the Łeba River.

www.oandhs.org

118 E. Szymczak, H. Piekarek-Jankowska

The considerable quantity of the river material transported, and in particular the bed load, was also indicated by the delta, which accumulates in the continuation of the mouth of the Reda River in the Puck Lagoon. At the moment, it is almost 700 m long, with a delta plain of approximately 400 m. The Reda delta is a young accumulation landform because the river mouth, which was used as recently as the late nineteenth century, was initially located approximately 1 km north of its current location. The process of delta formation depends on several factors, such as the relief of the delta background (catchment area), streamflow quantity, as well as the quantity and type of the river load, the manner in which the river enters the reservoir, wave motion, longshore currents, sea tides, reservoir bed features, and long-term changes in reservoir water level (Gradziński et al. 1986). All of these elements are responsible for the individual shape of the developing accumulation form. The Reda River’s delta plain, the accumulation of which was mainly influenced by river processes and wave motion (absence of tides), was marked by a small number of distribution channels (1–2) and periodically appearing sandy islands and barriers. In the mouth zone, the river water stream entered the waters of the Puck lagoon losing velocity and, as a result, depositing its load below the water level of the reservoir. The river waters of the Reda River were of lower density and therefore they dispersed in the surface layer in the form of a fan. The load was deposited near the mouth, but the fine fractions of the suspended sediment load were carried further. The deposition of the sandy fractions was indicated by the grain composition of the sediments deposited in the forefield of the mouth of the Reda River (Fig. 8) and was consistent with the sediments of the river channel deposited in the mouth stretch. The suspension content of lagoon waters in the Reda mouth zone decreased along with the distance from the mouth and changed from 18 to 5 g cm–3. It reached its peak value in the Reda channel (to more than 18 g cm–3) and in an inlet located between the Reda mouth and the Kanał Łyski, which was also a source of suspension (Fig. 9). A considerable decrease in the suspension content was recorded approximately 150 m from the mouth. An increase in the share of the organic fraction in the suspension and a decrease in the concentration of the suspension and in the bed zone (Fig. 10) was also recorded in the same area (Figs. 11, 12). These could have resulted from the process of flocculation, which took place in the area in which the fresh water of the Reda made contact with the brackish waters of the Puck Lagoon. Organic matter plays an important role in the flocculation and the creation of so-called “floccules” because it is adsorbed on the surface of clay minerals (Eisma et al. 1996). Under natural conditions, “floccules” grow to reach several millimeters and sometimes even several centimeters. Flocculation increases the suspension

The transport and distribution of the river load from the Reda River 119

Fig. 8. Bottom deposits in the area of the delta of the Reda River.

Fig. 9. Distribution of suspension [g m–3] in the surface water layer.

www.oandhs.org

120 E. Szymczak, H. Piekarek-Jankowska

Fig. 10. Share of the mineral fraction in the suspension (in %).

Fig. 11. Distribution of suspension concentration [g m–3] with depth in the area of the Reda River mouth.

Fig. 12. Percentage share of the organic fraction in the suspension in the area of the Reda River mouth.

The transport and distribution of the river load from the Reda River 121 deposition rate (Kranck 1984). The above was also confirmed by an increase in the share of the organic fraction in the delta sediments (Fig. 13). Generally speaking, the share of the organic fraction in bed sediments is lower than in the suspension, but this is most probably caused by its relatively fast mineralization and consumption by the bacteria and fauna living on the river bed (Eisma and Kalf 1987).

Fig. 13. Share of the mineral fraction in bottom deposits (in %).

CONCLUSIONS

The Reda River discharged a load of more than 9,900 tons annually into the Puck Lagoon. The size of the sediment inflow oscillated throughout the year. In the period from November to April, the sediment inflow was estimated to be 70%, which was connected directly to the river regime and streamflow. This resulted from the comparison of the mass of the suspended sediment load and the bed load in the traction transport that the bed load (rather than the suspended sediment load) dominated (73.5%) in the mouth stretch of the Reda River channel. The bed load included coarse-grained sands, with not more than 1% of organic matter. The main zone in which the traction transported material was deposited was located by the mouth, where an accumulative form, or delta,

www.oandhs.org

122 E. Szymczak, H. Piekarek-Jankowska formed. The grain-size composition of sediments in the delta slope reflected the bed load fraction of the river load. The structure of the suspended sediment load was dominated by fine- grained sediments - silt and clay - which constituted more than 90% of the suspended material. This type of load was also marked by a larger share of organic matter (approximately 59%), which was important for the flocculation that took place in the contact of fresh river waters and brackish sea waters.

REFERENCES

Allen P.A., 2000, Procesy kształtujące powierzchnię Ziemi, PWN, Warszawa, pp. 157-225, (in Polish) Augustowski B., 1974, Rzeźba terenu [in:] Studium geograficzno przyrodnicze i ekonomiczne województwa gdańskiego, Moniak J. (eds.), GTN, pp. 37-52, (in Polish) Bajkiewicz-Grabowska E., Magnuszewski A., Mikulski Z., 1993, Hydrometria, PWN, pp. 101- 256, (in Polish) Born A., 1928, Pomiary wielkości wleczenia materiału na dolnej Wiśle, Cz. Techn., pp. 2-4, (in Polish) Brański J., 1968, Zmącenie wody i transport rumowiska unoszonego w rzekach polskich, Prace PIHM, p. 95, (in Polish) Chen J., Li D., Chen B., Hu F., Zhu H., Liu C., 1999, The processes of dynamic sedimentation in the Changjiang estuary, J. of Sea Research, 41: 129-140 Cyberski J., 1980, Udział osadów rzecznych w bilansie materiału strefy przybrzeżnej, UG Geography Institute (manuscript), (in Polish) Cyberski J., 1982, Charakterystyka hydrologiczna, [in:] Dolina dolnej Wisły, Augustowski B. (ed.), GTN, pp. 103-153, (in Polish) Cyberski J., 1984, Zasoby wodne zlewni rzecznych [in:] Pobrzeże Pomorskie, Augustowski B. (ed.), Wyd. PAN, Warszawa, pp. 189-209, (in Polish) Cyberski J., 1993, Hydrologia zlewiska [in:] Zatoka Pucka, Korzeniewski K. (ed.), Fundacja Rozwoju UG, Gdańsk, (in Polish) Cyberski J., Jankowska H., 1984, Hydrologia zlewiska Zatoki Puckiej, Z. Nauk. WBiNoZ UG, 10: 4-31, (in Polish) Cyberski J., Szefler K., 1993, Klimat Zatoki i jej zlewiska [in:] Zatoka Pucka, Korzeniewski K. (ed.), Fundacja Rozwoju UG, Gdańsk, (in Polish) Dębski K., 1957, Obliczanie ilości rumowiska wleczonego w korycie Bugu w Wyszkowie, Wiad. Służby Hydrologicznej i Meteorologicznej, 5(3), (in Polish) Dynus-Angiel J., 1983, Typy uziarnienia rumowiska dennego rzek północnego skłonu Pomorza Zachodniego, Przeg. Geofizyczny, 28(2): 185-193, (in Polish) Eisma D., Kalf J., 1987, Distribution, organic content and particle size of suspended matter in the North Sea, J. of Sea Research 21: 265-285 Eisma D., Bale A.J., Dearnaley M.P., Fennessy M.J., Van Leussen W., Maldiney M.A., Pfeiffer A., Wells J.T. 1996, Intercomparison of in situ suspended matter (floc) size measurements, J. of Sea Research 36(1/2): 3-14 Fenster M.S., FitzGerald D.M., 1996, Morphodynamics, stratigraphy and sediment transport patterns of the Kennebec River estuary, Maine, USA, Sedimentary Geology, 107: 99-120 Friedrich M., 1984, Charakterystyka hydrologiczna zlewni Redy i Zagórskiej Strugi, Naczelna Organizacja Techniczna, Słupsk, (in Polish)

The transport and distribution of the river load from the Reda River 123

Gradziński R., Kostecka A., Radomski A., Unrug R., 1986, Zarys sedymentologii, Wyd. Geol., Warszawa, pp. 452-466, (in Polish) Islam M.R., Begum S.F., Yamaguchi Y., Ogawa K., 2002, Distribution of suspended sediment in the costal sea off the Ganges – Brahmaputra River mouth, observation from TM data, J. of Marine System, 32: 307-321 Jaeger J.M., Nittrouer C.A., 1995, Tidal controls on the formation of fine-scale sedimentary strata near the Amazon river mouth, M. Geology, 125: 259-281 Kondracki J., 1991, Typologia i regionalizacja środowiska przyrodniczego [in:] Geografia Polski środowisko przyrodnicze, Starkel L. (ed.), Wyd. Nauk. PWN, Warszawa, pp. 564-577, (in Polish) Kranck K., 1984, The role of flocculation in the filtering of particulate matter in estuaries [in:] The estuary as a filter, Kenedy V.S. (ed.), Ac. Press, pp. 159-175 Lajczak A., Jansson M.B., 1993, Seasonal variations in suspended sediment yield in the Baltic Sea drainage basin, Nordic Hydrology 24: 53-64 Li G., Tang Z., Yue S., Zhuang K., Wei H., 2001, Sedimentation in the shear front off the Yellow River mouth, Continental Shelf Research, 21: 607-625 Lopes J.F., Dias J.M., Dekeyser I., 2001, Influence of tides and river inputs on suspended sediment transport in the Ria de Aveiro Lagoon, Portugal, Phys. Chem. Earth, 26(9): 729- 734 Michalska B., 2004, Temperatury powietrza [in:] Atlas zasobów i zagrożeń klimatycznych Pomorza, Koźmiński C., Michalska B. (eds.), AR w Szczecinie, 30 p. 69, (in Polish) Milliman J.D., 2001, Delivery and fate of fluvial water and sediment to the sea: a marine geologist’s view of European rivers, Scientia Marina, 65: 121-132 Milliman J.D., Fransworth L.K., Albertin C.S., 1999, Flux and fate of fluvial sediments leaving large islands in the East Indies, J. of Sea Research, 41: 97-107 Milliman J.D., Syvitsky P.M., 1992, Geomorphic/tectonic control of sediment discharge to the ocean: The importance of small mountains rivers, J. of Geology, 100(5): 525-554 Nowacki J., 1976, Charakterystyka morfometryczna Zalewu Puckiego, Z. Nauk. WBGiO UG, Oceanografia, 3: 33-40, (in Polish) Nowacki J., 1993, Termika, zasolenie i gęstość wody [in:] Zatoka Pucka, Korzeniewski K. (ed.), Fund. Rozwoju UG, pp. 79-111, (in Polish) Ozga-Zielińska M., Brzeziński J., 1994, Hydrologia stosowana, PWN, Warszawa, p. 261, (in Polish) Ongley E., 1996, Sediment measurements [in:] Water Quality Monitoring – A Practical Guide to the Design and Implementation of Freshwater Quality Studies and Monitoring Programmes, Bartman J., Balladce R. (eds.), UNEP/WHO (http://www.who.int.docstore/water_sanitation_health/wqmonitor/ch15.htm) Pasławski Z., 1973, Metody hydrometrii rzecznej, WKiŁ, Warszawa, pp. 37-233, (in Polish) Pasternak K., Cyberski J., 1973, Skład granulometryczny unosin wód rzek karpackich na tle jakości podłoża ich zlewni, Problemy Zagospodarowania Ziem Górskich, 12: 131-152, (in Polish) Patchineelam S.M., Kjerfve B. Gardner L.R., 1999, A preliminary sediment budget for the Winyah Bay estuary, South Carolina, USA, M. Geology, 162: 133-144 Piekarek-Jankowska H., 1994, Zatoka Pucka jako obszar drenażu wód podziemnych, Wyd. UG, p. 104, (in Polish) Serrat P., Ludwig W., Nawarro B., Blazi J.L., 2001, Spatial and temporal variability of sediment fluxes from a coastal Mediterranean river: the Tet (France), Earth & Planetary Science, 333: 389-397 Skibiński J., 1976, Próba ilościowej oceny intensywności transportu rumowiska wleczonego w rzekach środkowej Polski, Z. Nauk. SGGW, 77, Warszawa, 111, (in Polish)

www.oandhs.org

124 E. Szymczak, H. Piekarek-Jankowska

Słomianko P., 1974, Warunki fizyczne regionu (Perspektywy rozwoju gospodarczego regionu) [in:] Zatoka Pucka, Słomianko P. (ed.), Studia i Materiały Oceanol., KBM PAN, 5: 8-67, (in Polish) Sottolichio A., Casting P., 1999, A synthesis on seasonal dynamics of highly concentrated structures in Gironde estuary, Earth & Planetary Science, 329: 795-800 Szymczak E., 2002, The transport of the material by the rivers on the northern slope of the Pomeranian Lake Land to the Baltic Sea, Oceanological Studies, 3-4: 85-97 Woodruff J.D., Rockwell Gever W., Sommerfield C.K., Driscroll N.W., 2001, Seasonal variation of sediment deposition in the Hudson River estuary, M. Geology, 179: 105-119