REFERENCE CONDITION OF RIVER REACHES FOR GEOMORPHOLOGICAL RESTORATION: OIARTZUN AND ORIA BASINS (GIPUZKOA)
Ibisate, A.1, Ollero, A.2, Sáenz de Olazagoitia, A.1, Acín, V.3, Granado, D.3, Ballarín, D.2,4, Herrero, X.1, Horacio, J.5, Mora, D.4 1
Geography, Prehistory and Archaeology Dept., University of the Basque Country, UPV/EHU; 2 Geography and Land Management Dept., University of Zaragoza; 3 ECOTER, S.C.; 4 MASTERGEO, S.L.; 5 Geography Dept., University of Concepción, Chile
[email protected]
1. INTRODUCTION
3. METHODOLOGY (continue)
4. RESULTS
Reference conditions and target images, based on the direct and indirect changes registered in the channel and basin (Wyżga et al., 2012), are needed for the restoration of river reaches (Brierley & Fryirs, 1995; Stoddard et al., 2006, Pardo et al., 2012) in order to achieve the good ecological status required by the Water Framework Directive 2000/60/CE.
2) Fluvial processes, pressures and impacts identification in the field. This information was used for the diagnosis of both watersheds in order to assess the hydrogeomorphological quality based on the IHG index (Ollero et al., 2008, 2011). Consequently, each river reach was identified as high, good, moderate, poor or bad hydrogeomorphological status according to the result of IHG index assessment (Fig. 3) .
89 combination types were found in the study area as result of crossing the 11 categories from the hydrogeomorphological reach-making and the 15 landscape categories. 39.7% of the reaches had “High” or “Good” hydrogeomorphological quality and were considered reference condition. 59.5% did not reach the good hydrogeomorphological quality. 18.6% has not any reference condition whereas a 19.8% has a reference condition reach just in one of the landscape combinations. The recovery potential assessment resulted that a 22.9% of the river reaches were irreversible, due to the severe number and density of impacts consequence of the very degraded areas that cross. On the other side, a 32% were reversible, most of them with a moderate hydrogeomorphological quality, but also some poor quality reaches that cross farming or forest and near-natural areas, were hydrogeomorphological restoration is more feasible (Fig. 5).
A methodology for the identification of river reach hydrogeomorphological reference conditions and target images and its application in two river basins, Oiartzun and Oria, is presented, for the river morphological restoration, as the basis for the recovery and restoration of habitats, as main goal. Fig. 3. Hydrogeomorphological quality assessment in both Oria (left) and Oiartzun (right) basins
2. STUDY SITE Both river basins are located in a mountain, rainy and steep area of the Basque Country, near the border to France (Fig. 1). The Oiartzun basin, in the northeastern area of Gipuzkoa county, has a surface of 85.27 km2. 35.04 km of its watershed has been studied: the Oiartzun River and its main tributaries. The Oria basin, of 881.99 km2, it is shared by two regions: Gipuzkoa and Navarra. Only the watershed located in Gipuzkoa county has been studied: the Oria River mainstream and its main tributaries, with a total length of 243.9 km. Fig. 1. Location of study area
3. METHODOLOGY The study has been based in an exhaustive field data collection and the analysis of that information through GIS tools, following the next steps: 1) Geomorphological homogeneous river reach identification for Oiartzun and Oria watersheds based on fieldwork data and with geomorphological criteria, adapted from the types proposed by Montgomery & Buffington (1997), Brierley & Fryirs (2005), Díaz Bea & Ollero (2005) and Horacio (2014). 11 channel types were identified in the study area: waterfalls, bedrock, step-pools, cascade, colluvial, run, riffle-pools, bedrock river with poolriffle sequences, bedrock river-colluvial, modified, and estuary (Fig. 2). Fig. 2. River reaches according to geomorphological types in both Oria (left) and Oiartzun (right) basins
3) Feasible reference condition identification of reaches that share hydrogeomorphological channel types, as well as landscape type, understood as channel types that have common lithology and land uses. 15 landscape types were identified, as the result of crossing the 5 categories in which lithology has been reclassified (carbonated rocks, granite and igneous rocks, unconsolidated sediment deposits, fine-grained consolidated clastic rocks, coarse-grained consolidated clastic rocks) and the 3 categories in which land uses were classified (forests and near-natural areas, farming areas and manmade areas). 4) The hydromorphological quality assessment (IHG) result of each river reach was crossed with landscape categories. Therefore, those river reaches with high or good assessment were considered reference condition for the river reaches that share the same landscape category and hydrogeomorphological channel typology. 5) Finally, target images for each river reach were suggested, as well as possible geomorphological restoration/rehabilitation measures, taking into account the hydromorphological processes that determine the recovery. 6) In some cases no reference conditions are found for all the river reaches. For those cases another methodology was applied: 6.1) Geomorphological reach-making for all the watersheds within Gipuzkoa county through GIS tools, crossing slope, sinuosity, fluvial dynamics and bed substrate (Fig. 4). 6.2) These reaches were crossed with landscape categories, as explained before and the ecological status assessment done by the Basque Water Agency.
Fig. 4. River reaches obtained through GIS tools for the whole watersheds of Gipuzkoa county
Fig. 5. Restoration potential of river reaches in both Oria and Oiartzun basins
10 restoration goals have been formulated based on the parameters analysed in the IHG index. These restoration goals were proposed according to the impacts and pressures identified in each river reach (Fig. 6).
Discharge diversions reduction or restriction Recovery of cut off or diverted reaches Improvement of slope and tributaries conectivity with the channel River bed topography naturalisation Reduction or removing of transversal obstacles Reduction or removing of barriers or dams that limit sediment movement Recovery of straightened reaches or set back of banks Reduction or removal of lands aboveground or other transversal barriers
Fig. 6. Number of reaches for each restoration goal
Recovery of natural morphology of banks Reduction or removal of dykes or lateral defenses without affection to… 0
10
20
30
40
50
60
70
80
The methodology based absolutely in GIS and applied for reaches without any reference condition was not very successful, due to the lowest precision of the input data for reach-making, the different length of the reaches, as well as the criteria for the quality assessment . ACKNOWLEDGMENTS This research is the result of several contracts funded and coordinated by the Gipuzkoa Provincial Council and signed with the University of the Basque Country (“Reference conditions for the restoration of fluvial morphology of Oiartzun River basin”, “Reference conditions for the restoration of fluvial morphology of Oria River basin”) and the University of Zaragoza (“Hydrogeomorphological reach identification of the rivers of Gipuzkoa”). We especially want to acknowledge the technicians of the Gipuzkoa Provincial Council involved in the project Patxi Tames, Felix Izco, Iñaki Bañares, Iñigo Mendiola, Andoni da Silva and Aitor Lekuona. We want to thank Josu Elso, Kristian Rey and Ángel Martínez Montecelo for the collaboration in the collection of field data. The authors also acknowledge the support from the Consolidated Research Group of the Basque Government IT 622-13, the Research and Formation Unit “UFI11/09. Cuaternario: Cambios Ambientales y Huella Humana” and the Research Group of the Aragón Regional Government “Clima, Agua, Cambio Global y Sistemas Naturales”
