4th World Water Forum

Transcription

1 4th World Water Forum Thematic Session 2.04: Shared Vision Models Model for nitrate management in the Ringkoebing Fjord catchment, Denmark By Henrik Larsen Head, Water Management,DHI Water & Environment & Torsten V. Jacobsen, DHI

2 Location Ringkoebing Fjord is a shallow fiord with a narrow connection to the North Sea The basin covers approximately 3,000 km2 on the west coast of Denmark The area is relatively flat with predominantly sandy deposits Land use is dominated by intensive agriculture and limited urban development.

3 History 1960 es: Quest for more agricultural land => draining of meadows. Lining of river. Largest draining project in Danish history es: Effects of draining: Increased nutrient loads to the fiord; algal growth, ochre pollution => fish kills; migratory birds disappear es: Environmental awareness leads to requirement for rehabilitation of the river 1998+: Implementation of the largest and most expensive nature rehabilitation project in Danish history.

4 How to do it? Previous studies: N-load N is the determining factor in pollution Agriculture is the major contributor: Nitrogen loads to Ringkoebing Fjord Agricultural N-load N must be reduced => negotiation w/ farmers But how much N-reduction?? N What is the effect in the fiord of 1 kg N removed?? How to maximise environment/$ spent?? Need for models as DSS!!

5 The Water Framework Directive perspective Project initiated to comply with national plans but aimed at serving as WFD tool Screening level and basic assessments Water management objectives Detailed water action plans Realistic target-setting: requires quantification tools Need for mathematical models

6 Integrated, multi-objective basin water management requires integrated models capable of addressing inter-related water resources and water quality issues. Model requirements Ground water and surface water - one hydrological system - one water resource - water quality status a function of both ground water and surface water Requires integrated management tools and models

7 Model objectives Development of distributed hydrology-,, load- and transport/decay models for the Ringkøbing Fjord basin to : 1) Simulate current annual nitrate loads to coastal waters 2) Identify areas which contribute most to pollution of the coastal waters and develop management strategy 3) Model effects of management scenarios in the basin (land use, wetlands, fertiliser application) - targets 35 % and 50 % reduction in total N loads to the fjord (political decision not model result!)

8 Management Model concept - integrated load, transport and degradation Input : Nitrate leakage from root zone Basin WQ model Grundvand Groundwater Shallow Øvre grundvand Groundwater Nedre Deep Groundwater grundvand Coastal Fjord waters Surface Overfladevand water Output Cost-benefit calculations of management scenarios Temp. Eng flooding Vådområde Wetland Vandløbsbund Riparian zone Sø Lakes WQ modeling of the fjord

9 Integrated basin transport model - concept for nitrate reduction Root zone Flow from drain channels and pipes Ground water Wetlands Transport through oxidized aquifer Transport through reduced aquifer

10 River network Skjern Å river restoration project MIKE11 setup expanded to cover entire basin (500 x 500 m GW model) Basin MIKE11 model Hydraulic model Routing model Not included Topography (m)

11 Pollution sources 1) Point source load time series in surface water (water treatment plants, fish farms and industry) 2) Non-point nitrate leakage data - field level time series aggregated into 500 m model grid Mean nitrate leakage for Ringkoebing Fjord basin (kgn/ha/day)

12 Basin monitoring and model results Nitrogen loads to Ringkoebing Fjord Model result

13 Scenario-setting discussed with stakeholders Scenario 1 : Areas of priority - identification of sub-areas of the basin where the highest effect of management intervention is obtained in terms of N-load reduction to coastal waters. Scenario 2: A targeted 35% reduction in nitrate loads by means of implementing the national program, 'Environmentally Friendly Agricultural Production'( MVJ) (7000 ha), reduced cash crops (5000 ha), reduced discharge from pump-drained areas, restored wetlands (4000 ha). Intervention is an estimate at this stage! Scenario 3: A targeted 50 % reduction in nitrate loads by means of all scenario 2 elements and an additional reduction in animal stock (29,000 animal units) in selected areas of the basin. Intervention is an estimate at this stage! Total nitrate leakage Current conditions Scenario 2 Scenario 3

14 Management areas of priority Basin MIKE11 model Hydraulic model Routing model Not included N load reduction effect Low Some High

15 Existing and restored wetlands according to scenario

16 Some model results Scenario 2 : The total N-load reduction of scenario 2 is 28 % compared to the targeted 35 %. The effect is primarily attributed to denitrification in wetlands and to a lesser degree to reduced nitrate leakage from agricultural land. Scenario 3 : The total N-reduction of scenario 3 is 33 % compared to the targeted 50 %. Important to incorporate the effect of all management initiatives in an integrated assessment. Nitrate removal in downstream wetlands is reduced when reducing nitrate leakage at field scale. New negotiations between authorities and stakeholders (ongoing)

17 Summary and Conclusions The MIKE11/SHE catchment model represents a comprehensive, integrated description of leakage, transport and degradation in surface water and ground water Possible to simulate total nitrogen load to Ringkøbing Fjord; Possible to identify areas of priority intervention based on the catchment model; Possible to simulate effects of distributed water management options with respect to load and concentrations - distributed in time and space for both groundwater and surface water Integrated water resources and water quality modeling is a valuable tool for WFD implementation - especially when looking at multiple pollutants and water bodies The model and the results of the study were successfully used as a DSS in negotiations between regional and national authorities and farmers and other stakeholders in defining management objectives and developing a plan for implementation.