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Measuring zero water level in stream reaches: A comparison of an image-based versus a conventional method
Hydrological Processes ( IF 3.2 ) Pub Date : 2022-08-09 , DOI: 10.1002/hyp.14658
Amelie Herzog 1 , Kerstin Stahl 1 , Veit Blauhut 1 , Markus Weiler 2
Affiliation  

A limited number of gauging stations, especially for nested catchments, hampers a process understanding of the interaction between streamflow, groundwater and water usage during drought. Non-commercial measurement devices can help overcome this lack of monitoring, but they need to be thoroughly tested. The Dreisam River in the South-West of Germany was affected by several hydrological drought events from 2015 to 2020 during which parts of the main stream and tributaries fell dry. Therefore it provided a useful case study area for a flexible longitudinal water quality and quantity monitoring network. Among other measurements the setup employs an image-based method with QR codes as fiducial marker. In order to assess under which conditions the QR-code based water level loggers (WLL) deliver data according to scientific standards, we compared its performance to conventional capacitive based WLL. The results from 20 monitoring stations reveal that the riverbed was dry for >50% at several locations and even for >70% at most severely affected locations during July and August 2020, with the north western parts of the catchment being especially concerned. Highly variable longitudinal drying patterns of the stream reaches emerged from the monitoring. The image-based method was found valuable for identification and validation of zero level occurrences. Nevertheless, a simple image processing approach (based on an automatic thresholding algorithm) did not compensate for errors due to natural conditions and technical setup. Our findings highlight that the complexity of measurement environments is a major challenge when working with image-based methods.

中文翻译:

测量河流中的零水位到达:基于图像的方法与传统方法的比较

数量有限的计量站,尤其是嵌套集水区,阻碍了对干旱期间径流、地下水和用水之间相互作用的过程理解。非商业测量设备可以帮助克服这种缺乏监控的问题,但它们需要经过彻底的测试。德国西南部的德雷萨姆河在 2015 年至 2020 年期间受到数次水文干旱事件的影响,部分干流和支流干涸。因此,它为灵活的纵向水质和水量监测网络提供了一个有用的案例研究区域。在其他测量中,该设置采用基于图像的方法,以 QR 码作为基准标记。为了评估基于 QR 码的水位记录仪 (WLL) 在哪些条件下根据科学标准提供数据,我们将其性能与传统的基于电容的 WLL 进行了比较。来自 20 个监测站的结果显示,在 2020 年 7 月和 8 月期间,多个地点的河床干涸超过 50%,在受灾最严重的地点甚至超过 70%,流域的西北部尤其受到关注。监测中出现了河流河段高度可变的纵向干燥模式。发现基于图像的方法对于零级事件的识别和验证很有价值。然而,一种简单的图像处理方法(基于自动阈值算法)并不能补偿由于自然条件和技术设置造成的错误。我们的研究结果强调,测量环境的复杂性是使用基于图像的方法时的主要挑战。
更新日期:2022-08-09
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