Hydromorphological Assessment as a Tool for River Basin Management: Problems with the German Field Survey Method at the Transition of Two Ecoregions

Abstract

Since the Water Framework Directive (WFD) came into force in 2000, data on the hydromorphological quality have been collected for all rivers in Europe. In Germany, a reference-based classification scheme is used (LAWA 2000) for hydrological assessment. The question arises whether this method can compensate sufficiently for a change of ecoregion. In our study of the Hase River in NW Germany, the frequency of the river classes was compared between two ecoregions (Lower Saxonian Mountains vs. Northwest-German Lowlands). In the lowlands, the evaluation shows a significantly higher proportion of class 5 river sections. This can mainly be attributed to the main parameters, longitudinal section, riverbed structure and bank structure. While the bad results in the longitudinal section and bank structure can be explained by changes in geology and anthropogenic pressures, the evaluation scheme cannot sufficiently compensate for changes in the riverbed structure. This problem is aggravated by the inconsistent implementation of the evaluation scheme in Germany, where the federal states use different approaches with regard to section length. Using 100 m sections throughout the river course can lead to severely underestimating the number of structures. Further improvement and standardization in the evaluation scheme seem to be necessary for the adjustment of the field survey method to different ecoregions in Germany.

Methodological Framework for Assessing Hydromorphological Conditions of Heavily Modified and Artificial River Water Bodies in Croatia

“…Furthermore, some studies have noted inconsistencies in assessing hydromorphological quality due to inadequate adaptation of the methodology to the regional hydromorphological characteristics of the rivers [40]. In this study, the applied indicators are generally in line with the indicators used in other hydromorphological assessment methodologies [34,35] but they are type-specific, i.e., their inclusion and score ranges are differentiated according to the established typology of the water bodies.…”

The impact of the geographical environment on the hydromorphological conditions of watercourses in southern Poland

“…A study by El Hourani et al (2022) showed significant differences between the mountain and lowland ecoregion in the case of the Hase River, Germany. The lowland sections showed a worse hydromorphological class than the mountain sections, which is partly due to natural factors (e.g.…”

Determination of River Hydromorphological Features in Low-Land Rivers from Aerial Imagery and Direct Measurements Using Machine Learning Algorithms

“…Depending on local conditions, this method was practiced in Austria, France, Finland, Italy, Portugal, and Slovenia [5,6]. Field measurements for hydromorphological unit data were used in earlier studies for Latvian [7,8], German [9,10], Polish [11] and Greek [12,13] rivers as well. A review of assessment methods for river hydromorphology was done by Belletti et al [14], identifying their main strengths, limitations, and the need for further improvements.…”

“…A review of assessment methods for river hydromorphology was done by Belletti et al [14], identifying their main strengths, limitations, and the need for further improvements. Thus, these regular surveys for river hydromorphology have certain limitations themselves; conducting them takes long time and requires considerable manpower as well [10,15]. Hydromorphological data collection can be facilitated by combining a laser rangefinder, geographic information system (GIS) and remote sensing methods [16][17][18].…”