Estimating Summer Low-Flow in Streams in a Morainal Landscape using Spatial Hydrologic Models

Abstract

This study evaluated the capability of four spatial hydrologic models to estimate summer lowflow stream discharge, as a surrogate for baseflow, and assessed the influence of land cover/land use on these flows, in small streams across the Oak Ridges Moraine. Low-flow discharge varied predictably with area of the upstream catchment, but also with reach slope and a measure of land cover disturbance (LDI). Low-flow volumes were lowest in streams with moderate agricultural and/or urban development (LDI of eight to 12%), and high over a range of development intensities. Each of Baseflow Index (BFI×Area), Darcy Index (DI), MODFLOW (MF) and a finer resolution MODFLOW model (FMF) were about equal in their capability to estimate low-flow discharge, with MF and FMF having a somewhat stronger relationship and Darcy Index having a somewhat poorer relationship, particularly in smaller catchments. Each of the models generally predicted low-flow discharge volumes to within about 400 L/s of the actual observed low-flow discharge. The models, therefore, were generally unable to predict whether a stream was flowing during periods of low-flow when the upstream catchment was smaller than about 17,800 ha. It was found that these methods cannot be reliably applied in small catchments as there is too much natural variability in flow conditions. This paper suggests that these methods do not reflect local conditions, but rather provide generalized information about water flows. As a result, it is recommended that until spatial model predictions are improved for local applications, water managers should invest in field surveys to confirm flow conditions in small catchments. Résumé : La présente étude avait pour objectif d'une part d'évaluer quatre modèles hydrologiques spatiaux afin d'en dégager la capacité d'estimation du débit d'étiage d'été, en tant que substitut du débit de base, et, d'autre part, d'évaluer l'incidence sur ces débits de la couverture terrestre et de l'affectation des terres dans les petits cours d'eau à l'échelle de la moraine d'Oak Ridges. Les débits d'étiage variaient de manière prévisible selon la zone du bassin hydrographique en amont, mais également selon la pente du bief et selon une mesure de la perturbation de la couverture terrestre (PCT). Les volumes en période que les prédictions du modèle spatial soient améliorées pour les applications locales, les gestionnaires de l'eau auraient intérêt à investir dans les études sur le terrain afin de confirmer les conditions d'écoulement dans les petits bassins hydrographiques.

Measuring function and structure of urban headwater streams with citizen scientists

“…We aggregated these proportions to calculate the landscape disturbance index (LDI) sensu Stanfield et al. (), a weighted proportion of disturbed land cover, where low LDI indicates a relatively undisturbed catchment (Appendix ). We also calculated a satellite‐derived continuous index of vegetation cover.…”

“…Land cover categories were taken from Agriculture and Agri-Food Canada (AAFC) (2015), which we found was more temporally accurate than other provincial land cover datasets despite a larger pixel sizes (30 m here vs. 10 m). We aggregated these proportions to calculate the landscape disturbance index (LDI) sensu Stanfield et al (2009), a weighted proportion of disturbed land cover, where low LDI indicates a relatively undisturbed catchment (Appendix S1). We also calculated a satellite-derived continuous index of vegetation cover.…”

Simulating cold-region hydrology in an intensively drained agricultural watershed in Manitoba, Canada, using the Cold Regions Hydrological Model

“…Poor model performance in dry years is not completely unexpected since low flows are generally more difficult to predict than larger flows (Nicolle et al, 2014), particularly for small catchment areas (Stanfield et al, 2009). This difficulty may also have been aggravated if there was flow under or over ice.…”

“…This pattern stresses the importance of internal snow redistribution within the watershed to stream discharge generation despite snow transport not impacting peak discharge to the same extent as blowing snow sublimation. The pattern also provides some insight into the potential for wind barrier sites such as shelterbelts to retain snow in upland areas (Steyn et al, 1997) to encourage infiltration and reduce runoff generation with melt.…”

Simulating cold-region hydrology in an intensively drained agricultural watershed in Manitoba, Canada, using the Cold Regions Hydrological Model

“…The model did not show satisfactory performance in dry years. Poor model performance in dry years is not completely unexpected since low flows are generally more difficult to predict than larger flows (Nicolle et al, 2014), particularly for small catchment areas (Stanfield et al, 2009). This difficulty may also have been aggravated if there was flow under or over ice.…”