Regionalization of patterns of flow intermittence from gauging station records

Abstract

Abstract. Understanding large-scale patterns in flow intermittence is important for effective river management. The duration and frequency of zero-flow periods are associated with the ecological characteristics of rivers and have important implications for water resources management. We used daily flow records from 628 gauging stations on rivers with minimally modified flows distributed throughout France to predict regional patterns of flow intermittence. For each station we calculated two annual times series describing flow intermittence; the frequency of zero-flow periods (consecutive days of zero flow) in each year of record (FREQ; yr −1 ), and the total number of zero-flow days in each year of record (DUR; days). These time series were used to calculate two indices for each station, the mean annual frequency of zero-flow periods (mFREQ; yr −1 ), and the mean duration of zero-flow periods (mDUR; days). Approximately 20 % of stations had recorded at least one zero-flow period in their record. Dissimilarities between pairs of gauges calculated from the annual times series (FREQ and DUR) and geographic distances were weakly correlated, indicating that there was little spatial synchronization of zero flow. A flow-regime classification for the gauging stations discriminated intermittent and perennial stations, and an intermittence classification grouped intermittent stations into three classes based on the values of mFREQ and mDUR. We used random forest (RF) models to relate the flow-regime and intermittence classifications to several environmental characteristics of the gauging station catchments. The RF model of the flow-regime classification had a cross-validated Cohen's kappa of 0.47, indicating fair performance and the intermittence classification had poor performance (cross-validated Cohen's kappa of 0.35). Both classification models identified significant environment-intermittence associations, in particular with regional-scale climate patterns and also catchment area, shape and slope. However, we suggest that the fair-to-poor performance of the classification models is because intermittence is also controlled by processes operating at scales smaller catchments, such as groundwater-table fluctuations and seepage through permeable channels. We suggest that high spatial heterogeneity in these small-scale processes partly explains the low spatial synchronization of zero flows. While 20 % of gauges were classified as intermittent, the flow-regime model predicted 39 % of all river segments to be intermittent, indicating that the gauging station network under-represents intermittent river segments in France. Predictions of regional patterns in flow intermittence provide useful information for applications including environmental flow setting, estimating assimilative capacity for contaminants, designing bio-monitoring programs and making preliminary predictions of the effects of climate change on flow intermittence.

Non-perennial Mediterranean rivers in Europe: Status, pressures, and challenges for research and management

“…NPRS are common in regions with low annual rainfall, high air temperature and steep, small and elongated catchments, which are not restricted to the dry Mediterranean region (Snelder et al, 2013). In some areas a strong decrease of the groundwater table has caused surface drying of entire river sections (EEA, 2009).…”

“…Efforts have been made to estimate the spatial distribution and extent of NPRS at the country (Snelder et al, 2013;Mulas et al, 2009;Regione Siciliana, 2010;Fig. 2), regional (Gómez et al, 2005) and river basin scales Rosado et al, 2012), though overlap in definition of intermittent, ephememeral and episodic systems is an issue.…”

“…One project specifically addressed biological assemblages and physico-chemical conditions in the Rhône-Alpes Region (Datry et al, 2014b). A second project attempted to model the distribution of NPRS reaches across the national hydrological network (Datry, 2012;Snelder et al, 2013). Another program predicted the effects of climate change on flow intermittency and biodiversity in two rivers located in the Mediterranean region of France (https://r2d2-2050.cemagref.fr/).…”

Flow Regime Classification and Hydrological Characterization: A Case Study of Ethiopian Rivers

“…The mean annual number of days with zero flow ratio (ZFRatio) is computed by dividing the mean annual number of days with zero flow by 365 [36,41]. This index has been widely used in river classification taxonomy [42].The mean day of the peak flow (PFday) is also the other variable that measures the time of the occurrence of the flood for the given station.…”

Ensemble reconstruction of spatio-temporal extreme low-flow events in France since 1871

“…The sub-division of France into HERs follows recent research (see e.g. Sauquet and Catalogne, 2011;Cipriani et al, 2012;Snelder et al, 2013 across HERs to derive spatio-temporal extreme low-flow events at the national scale.…”