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HYDROMORPHOLOGICAL ASSESSMENT OF THE LOWER HUNGARIAN DRAVA SECTION AND ITS FLOODPLAIN

The hydromorphological properties of rivers and their floodplains receive increased attention both in basic research and water management. A comparison of hydromorphological parameters before and after river regulation (involving floodplain drainage) provides important information for river management, particularly floodplain rehabilitation. The paper assesses a selected reach of the Drava River and the corresponding floodplain utilising two international approaches, the REFORM framework and the Italian Morphological Quality Index.


Introduction
River channelisation and the widespread agricultural utilization of floodplains led to landscape degradation, manifested in dropping groundwater table, gradual desiccation of soils, loss of wetlands, reduced floodwater retention capacity (Geilen et al. 2004) and a lower level of landscape diversity (Ward et al. 2002). As a commonly applied approach to river and floodplain management, Natural Water Retention Measures (NWRM) cover multi-purpose interventions: to protect water resources, to promote groundwater recharge through infiltration and regulating baseflow, to restore or maintain ecosystems as well as the closeto-natural state of water bodies (Schwarz 2014). The restored ecosystems equally contribute to the mitigation of and adaptation to climate change (Blanka et al. 2013) as well as to optimal water management (Brierley -Fryirs 2005).
The Drava floodplain belongs to groundwater-dependent ecosystems (GDEs), whose structure and functions basically rely on an adequate supply of groundwater (Kløve et al. 2012). The maintenance of an optimal groundwater table is made difficult by the conflicts between the demands of agriculture, forestry, flood control and nature conservation. For instance, if preregulation conditions, favourable for nature conservation and for flood hazard mitigation (FLUVIUS 2007), were restored, permanently high groundwater levels would deteriorate farmlands or make modern farming completely impossible and decrease productivity and yields in general (Kang et al. 2009). The pre-regulation channel pattern of the Drava River was well-developed meandering and locally anastomosing accompanied by a broad convex floodplain with natural levees, abandoned channels and backswamps (Kiss et al. 2011). Beginning with 1750, river channelization divided the area into an active and a "protected" floodplain. Cutoffs enhanced channel slope and current velocity and induced channel incision (Lóczy et al. 2014). With water balance fundamentally transformed in the floodplain, drought hazard has remarkably increased. Growing population density and infrastructural development also increased the vulnerability to flood and drought hazards.
Our aim was to provide a comprehensive hydromorphological assessment based on two international approaches. Such an assessment is useful as a background to environmental problems and as a tool to underpin rehabilitation measures (AQUAPROFIT 2005).

Methods
The Drava is a border river between Hungary and Croatia with an alluvial plain (morphological floodplain) of 696 km 2 area and 15-25 km width (VKKI 2010). On the 75-km long Hungarian section, there are 20 major side-channels, 13 tributary streams and 18 oxbow lakes (of ca 150 hectares total area -Pálfai 2001).
The hydromorphological character of the river and its floodplain along its lower Hungarian section is presented through the indicators of the EU project REFORM (REstoring Rivers FOR Effective Catchment Management) (González del Tánago et al. 2015) (Table 1) combined with another useful approach, the scoring system of the Morphological Quality Index (MQI), which has been successfully applied to the rivers of Italy (Rinaldi et al. 2013(Rinaldi et al. , 2015 ( Table  2). The contributors of these projects work in close cooperation. The REFORM framework describes changes compared to the conditions prior to river regulation. The MQI refers to an ideal state and is calculated from the equation MQI = 1 -S tot /S max , where S tot is the total score; S max is the maximum possible score.
The classes of morphological quality are defined as (Rinaldi et al. 2013 Since both methods were elaborated for reach-scale analysis, we selected a typical reach of the Lower Drava Plain, the environs of the Cún-Szaporca cutoff meander with oxbow lakes (Fig. 1), which are also in the focus of rehabilitation efforts within the Old Drava Programme (AQUAPROFIT 2005;DDKÖVÍZIG 2012).
In addition to our data acquisition data sources were water management documents

Results and discussion
Significant impact of human activities is manifested in the hydromorphological parameters of the river and its floodplain. The REFORM framework (Table 3) and in the MQI approach (Table 4) both point out fundamental changes (degradation) in river mechanism and floodplain connectivity, the role of aquatic and riparian vegetation and  Table 3. Classification and assessment of the pre-regulation and present conditions for the selected reach according to the REFORM framework Fig. 1. Location of the study reach opportunities for channel adjustment.
The comparison of pre-regulation and present conditions based on the REFORM method reveals a heavy modification of the river channel (geomorphological type, sinuosity, rate of incision) with severe impact on the floodplain too, manifested in both positive (reduction of flood-prone areas) and negative changes (degradation of riparian forests).
The MQI value for the studied Drava reach describes actual conditions. Its value was found to be 0.41, which qualifies poor in comparison with most Italian rivers. However, in Hungarian comparison this index value is suspected to be close to the national average for major rivers and floodplains.

Conclusions
Both hydromorphological assessment approaches have highlighted a high degree of transformation for the river and its floodplain compared to reference conditions (pre-regulation in the case of the REFORM framework or theoretical maximum scores in the case of the MQI). Further investigations are necessary to prove the applicability of the methods for the rivers of the Carpathian Basin.
Although these methods do not provide an envisioned target for rehabilitation efforts, detailed information are supplied for planners of such interventions. width of functional vegetation  wide strip of functional vegetation 0-3 1 F13 length of functional vegetation  functional vegetation all along the reach 0-5 0 A1 upstream alteration of flow significant alteration of flow by dams in upstream countries 0-6 5 A2 upstream alteration of sediment discharge significant reduction of sediment discharge by dams in upstream countries 0-6 6 A3 flow alteration in reach significant reduction of channel forming discharges 0-6 4 A4 sediment alteration in reach absence of sediment flux interception 0-6 0 A5 crossing structures no bridge in upstream vicinity (<1000 m) of reach 0-3 0 A6 bank protection rip-rap protection along the whole reach 0-12 12 A7 artificial levees levee along the whole reach 0-12 12 A8 changes of course meander cutoff 0-3 3 A9 bed stabilisation limited bed revetments 0-8 3 A10 sediment removal localised dredging in the past 20 years 0-6 3 A11 wood removal selective removal in the past 20 years 0-5 2 A12 vegetation management selective cuts in the past 20 years 0-5 2 CA1 adjustments in channel pattern major changes in channel pattern since 1950 0-6 4 CA2 adjustments in channel width limited changes since 1950 0-6 2 CA3 bed-level adjustments 2.4 m bed level change in 100 years 0-12 7 maximum score 158 Total score 94