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

Abstract

AbstractSpatial and temporal patterns of spring break‐up flooding in the Slave River Delta (SRD), Northwest Territories, are characterized during three years (2003–2005) using water isotope tracers and total inorganic suspended sediment (TSS) concentrations measured from 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 isotopically‐depleted δ18O (δ2H) signatures, ranging between − 19·2‰ (−145‰) and − 17·1‰ (−146‰) and most have high TSS concentrations (>10 mg L−1), while non‐flooded lakes have more isotopically‐enriched δ18O (δ2H) signatures, ranging between − 18·2‰ (−149‰) and − 10·6‰ (−118‰) 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. Calculations indicate river flooding caused dilution of ∼70–100% in delta lakes, while snowmelt dilution in the absence of river flooding ranged from ∼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 determining 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 historic, contemporary and future flood frequency in the delta. Copyright © 2008 John Wiley & Sons, Ltd.