Spatial and temporal perspectives on spring break-up flooding in the Slave River Delta, NWT

Spatial and temporal patterns of spring break-up flooding in the slave River Delta (SRD). Northwest Territories are characterized during three years (2003-2005) usign water isotope tracers and total inorganic suspended sediment (TSS) concentrations measured form lakewater samples collected shortly after the spring melt. Strongly contrasting spring melt periods led to a moderate flood in 2003, no flooding in 2004 and widespread flooding in 2005. Flooded lakes have isotopcally-depleted delta O-18(delta H-2) signatures, ranging between -19.2 parts per thousand (-145 parts per thousand) and -17.1 parts per thousand (-146 parts per thousand) and most have high TSS concentrations (>10 mg L-1) while non-flooded lakes have more isotopically-enriched delta 18O (delta 2H) signatures rnaging between -18.2 parts per thousand (-149 parts per thousand) and -10.6 parts per thousand (-118 parts per thousand) and low TSS concentrations (<10 mg L-1). These results in conjunction with the isotopic signatures of Slave River water and snowmelt are used to estimate the proportion of river- or snowmelt-induced dilution in delta lakes during the spring of each study year. Calculatins idicate river flooding caused dilution of similar to 70-100% in delta lakes, while snowmelt dilution in the absence of river flooding ranged form similar to 0-56%. A positive relationship exists between the spatial extent of spring flooding in the SRD and level and discharge on the slave river and upstream tributaries suggesting that upstream flow generation plays a key role in deltermining the magnitude of spring flooding in the SRD. parallel variations in the 46-year instrumental Slave River discharge record and flood stratigraphy in the active delta indicate that there is potential for extending the flood history of the SRD a development that will contribute to a more robust understanding of the drivers of histroic, contemporary and futrure flood frequency in the delta. Copyright (C) 2008 John Wiley & Sons. Ltd.