Determination of diurnal water level fluctuations in headwaters Marek Marciniak and Anna Szczucin ´ ska ABSTRACT The aim of this paper is to study diurnal fluctuations of the water level in streams draining headwaters and to identify the controlling factors. The fieldwork was carried out in the Gryz ˙ ynka River catchment, western Poland. The water levels of three streams draining into the headwaters via a group of springs were monitored in the years 2011–2014. Changes in the water pressure and water temperature were recorded by automatic sensors – Schlumberger MiniDiver type. Simultaneously, Barodiver type sensors were used to record air temperature and atmospheric pressure, as it was necessary to adjust the data collected by the MiniDivers calculate the water level. The results showed that diurnal fluctuations in water level of the streams ranged from 2 to 4 cm (approximately 10% of total water depth) and were well correlated with the changes in evapotranspiration as well as air temperature. The observed water level fluctuations likely have resulted from processes occurring in the headwaters. Good correlation with atmospheric conditions indicates control by daily variations of the local climate. However, the relationship with water temperature suggests that fluctuations are also caused by changes in the temperature-dependent water viscosity and, consequently, by diurnal changes in the hydraulic conductivity of the hyporheic zone. Marek Marciniak (corresponding author) Anna Szczucin ´ ska Institute of Physical Geography and Environmental Planning, Adam Mickiewicz University in Poznan ´, Dzięgielowa 27, 61-680, Poznan ´, Poland E-mail: mmarc@amu.edu.pl Key words | daily fluctuations, evapotranspiration, groundwater, headwaters, hyporheic zone INTRODUCTION In the temperate zone, annual changes in climatic con- ditions impose seasonal fluctuations of water levels observed for both surface and subsurface waterbodies. These fluctuations are induced primarily by natural water supply conditions, such as precipitation (e.g. Dobek ), melting of snow layers (e.g. Gribovszki et al. ), as well as by the yearly changes of evapotranspiration intensity (e.g. Goodrich et al. ; Czikowsky & Fitzjarrald ). The above-mentioned factors responsible for the vari- ations in surface water and groundwater levels have already been widely discussed in the literature. However, short- term, i.e. daily, changes have been examined less frequently. One of the key papers on this topic was published by Gri- bovszki et al. (), who linked the daily fluctuations in water level and discharge of streams to infiltration losses, precipi- tation (in tropical climate), melting and freeze-thaw processes (in polar zones and alpine areas) and evapotran- spiration (in temperate climates). Gribovszki et al. () found evapotranspiration to be the main factor influencing diurnal water level fluctuations in large river valleys. The effect of evapotranspiration on daily changes in the position of the water level was previously reported by such researchers as Troxell (), Wicht (), Tschinkel (), Lundquist & Cayan (), Loheide () and Szilágyi et al. (). Diurnal water level fluctuations may also be driven by the daily changes in atmospheric pressure (Turk ). Short-term variations in the shallow groundwater table and, in particular, the stream water level have also been con- sidered in the context of variable conditions of the hyporheic zone (Sophocleous ; Olsen & Townsend ; Packman & Selehin ; Runkel et al. ; Dong et al. ). In this contact zone between surface water 888 © IWA Publishing 2016 Hydrology Research | 47.4 | 2016 doi: 10.2166/nh.2016.039 Downloaded from https://iwaponline.com/hr/article-pdf/47/4/888/368304/nh0470888.pdf by guest on 16 June 2020