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This study examines stream modification efforts to increase the productive capacity of an isolated system of three small lakes in the Barrenlands region of Arctic Canada by enhancing system connectivity. The lakes' outlet streams were modified to create conditions favourable for fish passage and thereby promote migration among the lakes and the large lake into which they drain. Gabion step pools (in two streams) and a nature-like choke-and-pool structure (in one stream) were installed. Two years of post-construction hydraulics data were compared to data collected for two years prior to construction to determine the efficacy of the various stream modifications. Initial evaluations indicated unsuccessful performance of gabion step pools, so after the first year, they were retrofitted with boulders to increase flow depth, restrict discharge, improve flow duration, and create unimpeded connections rather than sudden drops. Variation of lake levels and duration, variability, and depth of stream flow indicated that outlet geometry and lake catchment area should be important considerations when enhancing connectivity for fish migration in ephemeral systems. A narrow, rectangular cross-section was deemed effective for increasing flow depth while decreasing discharge, resulting in increased duration of flows. Catchment area was an effective indicator of a headwater lake's potential response to connectivity enhancements. Smaller catchments may provide inadequate runoff to sustain minimum storage requirements for enhanced connectivity. Our findings should advance the knowledge of headwater system hydraulics in the Barrenlands and assist in designing future fish habitat compensation projects on similar systems. Key words: Arctic, ephemeral, freshet, habitat connectivity, headwater streams, nature-like fishpass. La presente etude examine la modification de ruisseaux afin d'ameliorer la capacite de production d'un systeme isole de trois petits lacs dans la toundra de l'arctique canadien en ameliorant la connectivite des systemes. Les effluents des lacs ont ete modifies pour creer des conditions favorables au passage des poissons et ainsi promouvoir la migration entre les lacs et le grand lac dans lequel ils se drainent. Des mares avec marches de gabion (dans deux ruisseaux) et une structure simili naturelle d'etranglement et d'etang (dans un ruisseau) ont ete installees. Des donnees hydrauliques, prelevees durant deux annees suivant la construction ont ete comparees a des donnees colligees sur deux annees avant la construction, afin de determiner l'efficacite des diverses modifications aux ruisseaux. Les evaluations initiales indiquaient un rendement inadequat des mares avec marches de gabion; alors, apres la premiere annee, des grosses roches ont ete ajoutees pour augmenter la profondeur d'ecoulement, restreindre la decharge, ameliorer la duree de l'ecoulement et creer des raccords non obstrues plutot que des chutes abruptes. La variation du niveau des lacs, la duree, la variabilite et la profondeur de l'ecoulement des ruisseaux indiquent qu'il faut tenir compte de la geometrie de l'exutoire et du bassin hydraulique du lac lorsque l'on desire augmenter la connectivite des systemes ephemeres pour la migration des poissons. Une section transversale rectangulaire etroite a ete jugee efficace pour augmenter la profondeur de l'ecoulement tout en diminuant la decharge, ce qui a augmente la duree des ecoulements. La superficie du bassin hydrologique etait un indicateur efficace de la reponse potentielle du lac amont a une meilleure connectivite. De plus petits bassins hydrologiques pourraient ne pas avoir un ruissellement adequat pour repondre aux exigences minimales de stockage pour une connectivite amelioree. Nos conclusions devraient permettre de faire progresser les connaissances sur l'hydraulique des bassins hydrauliques dans la toundra et aider a concevoir les futurs projets de compensation des habitats de poisson dans des systemes similaires. [Traduit par la Redaction] Mots-cles: arctique, ephemere, crue nivale, connectivite de l'habitat, eau d'amont des ruisseaux, passes migratoires semblables aux naturelles., 1. Introduction In ephemeral headwater systems, outlet elevation and geometry play important roles in governing lake storage thresholds and stream discharge. Modifying outlet characteristics will impact discharge, water storage, and [...]

The aim of this paper is to explore and describe a method of automated generalization designed to produce a map which strikes a balance between cartographic and hydrologic representations. Following a discussion of scholarly literature on generalization, we describe a novel method for automated generalization of hydrographic stream data, using the National Hydrography Data Set (NHDPlus) as an example. Traditional hydrography shows a fairly uniform density of stream flowlines over space. While this is pleasing to the eye, traditional methods tend to under-represent rivers in humid areas and over-represent them in arid areas. We address this problem through a method in automated generalization to produce a high-quality presentation of hydrographic data, suitable for display as a wall map or in an atlas. Streams are pruned based on a variable flow threshold, derived from the local mean annual precipitation by a regression equation. After running the model using different parameters, we produce a more satisfactory portrayal of stream networks in the United States that communicates the flow of water through rivers and reflects the regional climate. Specific advantages in generalizing with variable flow threshold include (1) the method allows for fine gradations in output scale; (2) the output maps tend to minimize density variations in the raw data; (3) the subjective criteria are easily derived; and (4) the method can be performed rapidly on large data sets, as long as the stream data has been enriched with reliable flow rates. Keywords: generalization; hydrography; National Hydrography Data Set; NHDPlus, Introduction Hydrography is a conspicuous and complex natural theme on topographic maps due to its large number of features (Savino et al. 2011). It must be drawn with strict tolerances [...]