Abstract
Abstract. Understanding the spatial distribution of discharge can be important for water quality and quantity modeling. Non-steady flood waves can, particularly as a result of short high intensity summer rainstorms, influence small headwater streams significantly. The aim of this paper is to quantify the spatial and temporal dynamics of stream flow in a headwater stream during a summer rainstorm. These dynamics include gains and losses of stream water, the effect of bypasses that become active and hyporheic exchange fluxes that may vary over time as a function of discharge. We use an advection-dispersion model coupled with an energy balance model to simulate in-stream water temperature, which we compare with high resolution temperature observations obtained with Distributed Temperature Sensing. This model was used as a learning tool to stepwise unravel the complex puzzle of in-stream processes subject to varying discharge. Hypotheses were tested and rejected, which led to more insight in the spatial and temporal dynamics in discharge and hyporheic exchange processes. We showed that, for the studied stream infiltration losses increase during a small rain event, while gains of water remained constant over time. We conclude that, eventually, part of the stream water bypassed the main channel during peak discharge. It also seems that hyporheic exchange varies with varying discharge in the first 250 m of the stream; while further downstream it remains constant. Because we relied on solar radiation as the main energy input, we were only able to apply this method during a small summer storm and low flow conditions. However, when additional (artificial) energy is available, the presented method is also applicable in larger streams, during higher flow conditions or longer storms.
Highlights
Understanding discharge generation processes in headwater catchments is crucial for water quality and quantity modeling (Bonell, 1998)
During the second step of the calibration we focus on different processes that occur during the second discharge peak, which we assume is subsurface storm flow originating from the area upstream of the upstream V-notch weir
The difference in the RMSET was mainly caused by the fact that during the calibration period the fiber optic cable was not submerged at a few distinct places
Summary
Understanding discharge generation processes in headwater catchments is crucial for water quality and quantity modeling (Bonell, 1998). A classical way to do this is by hydrograph separation using endmember mixing analysis approach (Sklash and Farvolden, 1979). This technique can be useful in differentiating between different source areas or between event and pre-event water (Uhlenbrook and Hoeg, 2003). Understanding the spatial distribution of discharge can be important since non-steady flood waves can influence small headwater streams significantly, as a result of short high intensity summer rainstorms. During such events, discharge can more than double, and side channels can become active. Subsurface storm flow may occur, a certain storage threshold in the hillslope has to be passed before this mechanism becomes active (e.g. Trompvan Meerveld and McDonnell, 2006)
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