Spatial coherency of the spring flood signal among major river basins of eastern boreal Canada inferred from flood rings

摘要

In eastern boreal Canada, long-term perspective in water resources and hydroelectric dam management is currently limited by the lack of long-term hydrological records. The research for new paleohydrological proxies would help fill this hydrological data gap and provide regional hydroclimatic predictive trajectories in the context of climate change. The development of long annually resolved series of earlywood vessel cross-sectional area has recently demonstrated a high potential for reconstructing high and low discharges. This study analyzes a network of 10 sites scattered around Lake Duparquet. The region covers an area of about 20 000 km(2) including four river basins characterized by natural and regulated rivers, and unflooded control sites. The objectives were to assess 1) the spatial coherency in flood-rings chronologies among sites and Lake Duparquet, and among hydrological regimes (natural, regulated and unflooded control) and 2) their degree of association with i) annually resolved chronologies of earlywood vessel cross-sectional area and number, ii) a reconstruction of the Harricana River spring discharge and iii) discharge data from eleven hydrometric stations distributed in the study area. It was hypothesized that flood rings would be consistent among natural rivers and absent from regulated rivers. Results showed high spatial coherency among natural rivers with flood rings recording the major floods of the last 250 years. Flood ring and earlywood vessel chronologies were strongly correlated to both reconstructed and instrumental discharge data. On regulated rivers, trees were younger than at the other sites and mainly spring floods that occurred prior to dam creation and the few extreme floods after dam creation were recorded by flood rings. One hypothesis is that older trees (before dam) most likely recorded the natural dynamic of the river, while younger trees (after dam) most likely recorded dam management maneuvers and spring flood exceeding dam capacity. Flood rings and earlywood vessel chronologies provided comparable and complementary hydrological evidence. Flood rings were easily identified visually allowing fast determination of major flood years whereas developing earlywood vessel chronologies, while being more tedious and time consuming, allowed capturing a larger spectrum of hydrological conditions