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<p>Logjams increase hydraulic resistance and create hydraulic head gradients along the streambed that drive groundwater-surface water exchange. Here, we quantify changes in hyporheic exchange flow due to channel-spanning logjams using field measurements and numerical modeling in MODFLOW and MT3DMS. Electrical resistivity (ER) imaging was used to monitor the transport of solutes into the hyporheic zone during a series of in-stream tracer tests supplemented by in-stream monitoring. We conducted experiments in a variety of reaches in Little Beaver Creek, Colorado (USA) of varying complexity: a control reach with no logjams, a reach with a single, channel-spanning logjam, and additional jams with greater logjam complexity. Our results show that 1) higher hyporheic exchange flow occurs at reach with logjams, 2) logjams create complex hyporheic exchange flow pathways that can cause bimodal solute breakthrough behavior downstream, and 3) higher discharge rates associated with spring snowmelt increase the extent and magnitude of hyporheic exchange flow. The numerical modeling supports all three field findings, and also suggest that lower flows increase solute retention in streams, although this last conclusion is not strongly supported by field results. This study represents the first use of ER to explore hyporheic exchange flow around a naturally occurring logjam over different stream discharges and has implications for understanding how logjams influence the transport of solutes, the health of stream ecosystems, and stream restoration and conservation efforts.</p>

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"What matters gets measured" "You can't manage what you don't measure". When it comes to Ontario's groundwater resources these old adages certainly strike a chord. What do we really know about our groundwater systems? Have we been sufficiently measuring and monitoring the resource? Do we effectively integrate some 50 years of previous knowledge into day to day decision making? Since 2001, the long standing Oak Ridges Moraine Groundwater Program (ORMGP - formerly referred to as YPDT-CAMC Groundwater Management Program) has been working to: i) assemble a comprehensive and reliable source of groundwater related data; ii) bring critical analyses to the data; and iii) construct a geological and hydrogeological framework into which new drilling and information can be incorporated. The results of this work are being made available through an interactive website where numerous 'themed' maps (e.g. geology, water levels, documents, etc.) intuitively provide ready access to the program's data and interpretive geological and hydrogeological framework. As an integral part of the program's over-arching goal of improving upon water management decision-making in Ontario, an ongoing process is to engage practitioners on a variety of levels to arrive at a point where regular contributions of data, insight and information are returned back to this 'actively managed' program, thus improving the hydrogeological knowledge-base for the broader community.