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Fluvial drainage patterns in orogenic belts reflect interactions among tectonics, climate, and lithology. The central South Tian Shan displays a complex fluvial drainage pattern that shifts from longitudinal (flowing parallel to mountain ranges) in the west to transverse (flowing across ranges) in the east. Whether such drainage patterns reflect underlying patterns of tectonic deformation, lithology, climate, or the influence of surface processes within a drainage basin is often unclear. We focus here on the large Saryjaz catchment of SE Kyrgyzstan, which marks the transition between longitudinal and transverse drainages. We analyse topographic and fluvial metrics including slope, river steepness (ksn), and the integral proxy (χ) along the river profile, and we map the spatial distribution and characteristics of knickpoints to discern the possible controls on the observed drainage pattern. We discriminate between knickpoints of different origin, namely tectonic, lithologic, glacial, and those linked to transient waves of incision. We find a series of transient knickpoints in tributaries downstream of a sharp 180° bend in the main stem of the Saryjaz river, which also marks a striking increase in channel steepness. Both observations indicate accelerated incision along this lower reach of the catchment. Knickpoint elevations and ksn below the knickpoints decrease downstream, whereas χt values of knickpoints (χ measured from the tributary junctions) remain near-constant among tributaries. These results, together with a comparison of other rivers in the vicinity that show no evidence of transient knickpoints, suggest that transient incision in the Saryjaz catchment is driven “top-down” by a large-magnitude river capture event rather than “bottom-up” by accelerated uplift or base-level fall. We estimate an erodibility parameter from 10Be-derived catchment-average denudation rates and use this to estimate the celerity of knickpoints. We find that the knickpoints started retreating at a similar time between ca. 1.5 and 4.4 Myr ago. Considering the river patterns and the timing constraints, we suggest that this capture event was likely driven by the overfill of Neogene intermontane basins, potentially affected by both tectonic and climate factors.

Abstract Alluvial rivers aggrade, incise, and adjust their sediment‐transport rates in response to changing sediment and water supply. Fluvial landforms, such as river terraces, and downstream stratigraphic archives may therefore record information about past environmental change. Using a physically based model describing sediment transport and long‐profile evolution of alluvial rivers, we explore how their responses to environmental change depend on distance downstream, forcing timescales, and whether sediment or water supply is varied. We show that amplitudes of aggradation and incision, and therefore the likelihood of terrace formation, are greater upstream and in shorter and/or wetter catchments. Aggradation and incision, and therefore terrace ages, may also lag behind environmental change. How sediment‐transport rates evolve depends strongly on whether water or sediment supply is varied. Diverse responses to environmental change could arise in natural alluvial valleys, controlled by their geometry and hydrology, with important implications for paleo‐environmental interpretations of fluvial archives.

Objective: In a randomized trial, we sought to determine whether 2% clindamycin cream administered intravaginally during labor to group B streptococcal-colonized pregnant women without risk factors would decrease maternal and neonatal colonization.