Ditch the low flow: Agricultural impacts on flow regimes and consequences for aquatic ecosystem functions

Global warming has a profound influence on global and regional water cycles, especially in the cold mountainous area. However, detecting and quantifying such changes are still difficult because noise and variability in observed streamflow are relatively larger than the long-term trends. In this study, the impacts of global warming on the catchment water cycles in the Yarlung Zangbo River Basin (YZRB), one of most important catchments in south of the Tibetan Plateau, are quantified using a climatic approach based on the relationship between basin-scale groundwater storage and low flow at the annual time scale. By using a quantile regression method and flow recession analysis, changes in low flow regimes and basin-scale groundwater storage at the Nuxia hydrological station are quantified at the annual time scale during 1961–2000. Results show annual low flows (10th and 25th annual flows) of the YZRB have decreased significantly, while long-term annual precipitation, total streamflow, and high flows are statistically unchanged. Annual lowest seven-day flow shows a significantly downward trend (2.2 m3/s/a, p < 0.05) and its timing has advanced about 12 days (2.8 day/10a, p < 0.1) during the study period. Estimated annual basin-scale groundwater storage also shows a significant decreasing trend at a rate of 0.079 mm/a (p < 0.05) over the study period. Further analysis suggests that evaporation increase, decreased snow-fraction, and increased annual precipitation intensity induced by the rising temperature possibly are the drivers causing a significant decline in catchment low flow regimes and groundwater storage in the study area. This highlights that an increase in temperature has likely already caused significant changes in regional flow regimes in the high and cold mountainous regions, which has alarming consequences in regional ecological protection and sustainable water resources management.

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Optimised Triangular Weir Design for Assessing the Full-Scale Performance of Green Infrastructure

Water ◽

10.3390/w11040773 ◽

2019 ◽

Vol 11 (4) ◽

pp. 773

Author(s):

Mohamad H. El Hattab ◽

Ana Mijic ◽

Dejan Vernon

Keyword(s):

Green Infrastructure ◽

Discharge Coefficient ◽

Flow Regimes ◽

Full Scale ◽

Performance Estimation ◽

Low Flow ◽

Site Conditions ◽

Flow Measurements ◽

Flow Rates ◽

Accuracy Of Measurements

Conventional triangular weirs have been originally developed to measure, divert, and control surface water. However, a special application of these weirs, such as for low flow measurements in full-scale monitoring of Green Infrastructure (GI), is not well investigated. Available head-discharge relationships for triangular sharp-crested weirs are only valid under a free-flow regime. Literature focusing on the V-notch weir usage for GI assessment suggests that it is necessary to calibrate the head-discharge relationship before its use. This study focuses on understanding the effects of site constraints on the measurement performance of a V-notch weir at low flow rates, and the validity of equations derived for similar applications that can be found in the literature. The variation of discharge coefficient in various flow regimes was investigated experimentally based on calibration runs covering flow rates between 0.054 l/s and 7 l/s. The results show that for 30° and 45° V-notch weirs, three flow regimes can be identified. It was observed that literature equations to calculate the discharge coefficient are valid for partially-contracted triangular weirs only at heads greater than vertex distance from the channel. However, for low flows that are expected to occur when estimating the full-scale performance of GI, the equations available from the literature for similar site conditions underestimated the flow rate between 85% and 17%. This emphasises the need for accurate calibration of a V-notch device under the site conditions to achieve the necessary level of accuracy in GI performance estimation. The procedure outlined in this work can be easily replicated to determine the optimal monitoring system configuration. Alternatively, if the site conditions would match those described in this study, the computed discharge using the proposed relations, in combination with the general V-notch weir equation, provides a significant improvement in the accuracy of measurements, expands the head applicability range of V-notch weirs, and enables better understanding of GI performance at the full scale.

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Stability of River Flow Regimes

Hydrology Research ◽

10.2166/nh.1992.0010 ◽

1992 ◽

Vol 23 (3) ◽

pp. 137-154 ◽

Cited By ~ 29

Author(s):

I. Krasovskaia ◽

L. Gottschalk

Keyword(s):

Climate Change ◽

Flow Regime ◽

Climate Models ◽

River Flow ◽

Flow Regimes ◽

Low Flow ◽

Future Climate Change ◽

Mean Annual Temperature ◽

Economic Policies ◽

Temperature And Precipitation

One of the most important consequences of future climate change may be an alteration of the surface hydrological balance, including changes in flow regimes, i.e. seasonal distribution of flow and especially the time of occurrence of high/low flow, which is of vital importance for environmental and economic policies. Classification of flow regimes still has an important role for the analyses of hydrological response to climate change as well as for validating climate models on present climatic and hydrologic data, however, with some modifications in the methodology. In this paper an approach for flow regime classification is developed in this context. Different ways of flow regime classification are discussed. The stability of flow regimes is studied in relation to changes in mean annual temperature and precipitation. The analyses have shown that even rather small changes in these variables can cause changes in river flow regimes. Different patterns of response have been traced for different regions of the Nordic countries.

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International assessment of future low-flow regimes and their impact on three water-related sectors in the Meuse basin – a collaborative approach

International Journal of River Basin Management ◽

10.1080/15715124.2014.983523 ◽

2014 ◽

Vol 13 (1) ◽

pp. 123-135 ◽

Cited By ~ 1

Author(s):

Alexandra Bauwens ◽

Aurore Degré ◽

Deborah Deraedt ◽

Ricarda Döring ◽

Gilles Drogue ◽

...

Keyword(s):

Flow Regimes ◽

Low Flow ◽

Collaborative Approach ◽

International Assessment

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A geological framework for interpreting the low-flow regimes of Cascade streams, Willamette River Basin, Oregon

Water Resources Research ◽

10.1029/2003wr002629 ◽

2004 ◽

Vol 40 (4) ◽

Cited By ~ 148

Author(s):

Christina Tague ◽

Gordon E. Grant

Keyword(s):

River Basin ◽

Flow Regimes ◽

Low Flow ◽

Willamette River ◽

Willamette River Basin

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Mean flow velocity in the Nile River, Egypt: an overview of empirical equations and modification for low-flow regimes

Hydrological Sciences Journal ◽

10.1080/02626667.2020.1853732 ◽

2020 ◽

pp. 1-13

Author(s):

Fahmy S. Abdelhaleem ◽

Ahmed M. Amin ◽

Esam Y. Helal

Keyword(s):

Flow Velocity ◽

Flow Regimes ◽

Low Flow ◽

Nile River ◽

Empirical Equations ◽

Mean Flow ◽

Mean Flow Velocity

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Both Forest Harvesting and Hydropower Dams Yielded Negative Impact on Low Flow Regimes in the Zagunao River Watershed, Southwest China

Forests ◽

10.3390/f11080787 ◽

2020 ◽

Vol 11 (8) ◽

pp. 787

Author(s):

Zhiwei Jiang ◽

Mingfang Zhang ◽

Yiping Hou

Keyword(s):

Return Period ◽

Negative Impact ◽

Flow Regimes ◽

Forest Harvesting ◽

Forest Recovery ◽

Low Flow ◽

River Watershed ◽

Low Flows ◽

Hydropower Dams ◽

The Impact

Forest harvesting and hydropower dams can significantly affect flow regimes (magnitude, timing, duration, frequency, and variability), resulting in changes in degraded aquatic ecosystems and unstable water supply. Despite numerous studies on the effects of forest harvesting on mean flows, the impact of forest harvesting on flow regimes has been less investigated. A great difficulty lies in separating the hydrological effect of forest harvesting from that of climate variability and other watershed disturbances such hydropower dams. In this study, the Upper Zagunao River watershed (2242 km2) was selected as an example to provide a quantitative assessment of the effects of forest harvesting and hydropower dams on low flow regimes. The key findings include: (1) Forest harvesting led to a significant reduction in the magnitude and return period of low flows, and a significant increment in the variability and duration of low flows; (2) the recovery of low flow regimes occurred 40 years after forest harvesting as forest recovery processed; and (3) hydropower dams caused significant impact on all components of low flow regimes, e.g., a reduction in the magnitude, return period, and timing of low flows, and an increment in the variability and duration of low flows. Our findings highlight the negative impact of both forest harvesting and hydropower dams on low flow regimes in the Upper Zagunao River watershed. A watershed management strategy for offsetting the negative effect of hydropower dams on low flow regimes by restoring hydrological functions of subalpine forests is highly recommended in subalpine watersheds of the Upper Yangtze River.

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Morphological dynamics of ureteral transport. II. Peristaltic patterns in relation to flow rate

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1989.256.1.r29 ◽

1989 ◽

Vol 256 (1) ◽

pp. R29-R34 ◽

Cited By ~ 3

Author(s):

L. Ohlson

Keyword(s):

Flow Rate ◽

Flow Regimes ◽

High Flow ◽

Low Flow ◽

Contact Period ◽

Tube Flow ◽

Flow Rates ◽

Open Tube ◽

Normal Human ◽

Points Of Resistance

To study in the human the conditions for the flow regimes inherent in urinary systems with a dependence of the contraction interval on urine flow rate (boluses-in-contact, leaky-bolus, and open-tube flow regimes), 50 urinary systems were examined at low and high flow rates. Morphometry and volumetry were applied to eight urinary systems. The bolus frequently contacted the preceding contraction ring but the mechanisms differed categorically from that conventionally postulated. Thus the contraction interval proved independent of flow rate, leading to boluses in contact not only at high but also at low flow rates, which is impossible in flow-dependent urinary systems. Likewise, contact proved possible with small as well as large boluses. Furthermore, the contact was invariably interrupted at the points of resistance to flow, the total contact period being only 4% of the ureteral transit. Leaky-bolus flow and open-tube flow were absent. The flow regimes as conventionally defined thus proved to be absent from and inconsistent with normal human urinary transport.

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