Implementing the Water Framework Directive to temporary rivers

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Alternative methods for the estimation of the regime of temporary rivers 

The Life + TRIVERS team just published a paper in Science of the Total Environment that tries to use two alternative methods for gathering information on the regime of temporary streams: interviews made to the neighbors of the river reach, and the inspection of aerial photographs. The combination of the two alternative methods allows substituting or complementing flow records, to be updated in the future through monitoring by professionals and citizens.

Hydrological data for assessing the regime of temporary rivers are often non-existent or scarce. The scarcity of flow data makes impossible to characterize the hydrological regime of temporary streams and, in consequence, to select the correct periods and methods to determine their ecological status. This is why the TREHS software is being developed, in the framework of the LIFE+ Trivers project. It will help managers to implement adequately the European Water Framework Directive in this kind of water body.

TREHS, using the methodology described in Gallart et al. (2012), defines six transient 'aquatic states', based on hydrological conditions representing different mesohabitats, for a given reach at a particular moment. Because of its qualitative nature, this approach allows using alternative methodologies to assess the regime of temporary rivers when there are no observed flow data. These methods, based on interviews and high-resolution aerial photographs, were tested for estimating the aquatic regime of temporary rivers.

All the gauging stations (13) belonging to the Catalan Internal Catchments (NE Spain) with recurrent zero-flow periods were selected to validate this methodology. On the one hand, non-structured interviews were conducted with inhabitants of villages near the gauging stations (Figure 1). On the other hand, the historical series of available orthophotographs were examined (Figure 2). Flow records measured at the gauging stations were used to validate the alternative methods.

Figure 1 ENG

Figure 1: Core information obtained in one of the interviews. The figures in the table represent the long-term number of months for every condition in the respective season. The figures at the bottom show the resulting metric values; Mf = Permanence of flow, Sd6 = Predictability of the dry season, Mp = Permanence of pools.

Flow permanence in the reaches was estimated reasonably by the interviews and adequately by aerial photographs, when compared with the values estimated using daily flows. The degree of seasonality was assessed only roughly by the interviews. The recurrence of disconnected pools was not detected by flow records but was estimated with some divergences by the two methods.

Figura2

Figure 2: Aerial photographs of the Manol River near the Santa Llogaia gauging station. The left image shows continuous flow, the middle one disconnected pools and the right one dry stream bed. The North is towards the left site and the height of the images is 500 m. Source: ICGC.

Citation:
Gallart F, Llorens P, Latron J, Cid N Rieradevall M, Prat N (2016). Validating alternative methodologies to estimate the regime of temporary rivers when flow data are unavailable. Science of the Total Environment, 565:1001-1010. doi: 10.1016/j.scitotenv.2016.05.116