AGRICULTURAL CATCHMENTS

Transcription

1 EXTREME RUNOFF CONDITIONS IN SMALL AGRICULTURAL CATCHMENTS Johannes Deelstra, Hans Olav Eggestad, Bioforsk, Norway. Arvo Iital,Tallinn University of Technology, Estonia. Viesturs Jansons, Latvia University of Agriculture

2 What are extreme runoff events Too much rain Too little rain Change in winter, freeze/thaw cycles All can have the same effect Deteriorating water quality

3 Baltic Sea, the worlds sickest sea! 25% considered dead kt/article ece 8 Räpu river Jänijõgi NO3-N, mg/l mg NO 3 -N l

4 What did we do and why? How long does it take to get the water/nutrients/soil out of the catchment, What happens when considering daily versus hourly discharge values? Does one loose information? Is hydrology in small agricultural catchments different from larger catchments? What are the flow paths in small agricultural ral catchments How does hydrology influence soil and nutrient losses

5 Location of catchments

6 Catchment Catchment characteristics Size (ha) Normal temp. (ºC) Normal prec. (mm) Main crops Høgfoss Cereals (19%) Skas Heigre Ley (80%) Hotran Cereals (60%) Mørdre Cereals, ley (65%) Skuterud Cereals, ley (62%) Kolstad Cereals, ley(68%) Volbu Ley, fodder(42%) Naurstad Ley((42%) Vasshaglona Vegetables (60%) Nyhaga Forest Vandsemb (subsurface drainage) 6, Cereals (100%) Bye (subsurface drainage) Cereals, pot. (100%) Vinningland (subsurface drainage) Ley (100%) Räpu (Estonia) Cereals, ley (77%) Rägina (Estonia.) Ley, cereals, (53%) Mellupite catchment.(latvia) Cereals (68%) Mellupite (subsurface drainage,latvia) Cereals(100%)

7 Runoff and nutrient loss

8 Seasonality in runoff Catchment Winter Spring Summer Autumn Dec - Feb Mar - Apr May - Aug Sept - Nov Høgfoss Skuterud, Kolstad Vandsemb Vinningland Räpu (Est.) Mellupite drainage (Lat.)

9 Accumulated runoff and nutrient loss, Skuterud catchment, Norway Skuterud Høgfoss runoff SS TP TN runoff % days % days

10 Characteristic for smaller catchments; large in-day variation in runoff When this is the case how do we present runoff data, fe maximum yearly flow values Average daily discharge? Maximum daily discharge

11 Maximum specific discharge; Skuterud and Høgfoss Size;4.5 km^2 Size; 295 km^2

12 The flashiness index Flashiness, or rate of change, refers to how quickly flow changes from one condition to another. day hour FI day = n i= 1 q i n i= 1 q i q n i 1 i= 1 FI hr = n i q q i hr

13 The flashiness index

14 Why differences in FI Main reasons are; Topography Size of catchment Geology Soil types Drain spacing

15 Flashiness index, baseflow index and nutrient losses Catchment Nitrogen Phosphorus FI BFI Räpu Rägina Mørdre Skuterud

16 Flashiness, an example Winter runoff (Øygarden, 2000) January 30 January 31 Runoff: 25 mm Runoff: 77 mm Soil loss: 2 kg ha - 1 Soil loss: kg ha -1

17 Runoff, erosion o and nutrient t loss in small catchments and climate change Prediction for south-eastern Norway; Drier summer, milder winter + more precipitation Seasonality showed little runoff during summer What will happen with the winter

18 How to define a winter period? What is a winter?

19 Variation in freezing index V i ti i f /th Variation in freeze/thaw cycles

20 Milder winter more freeze/thaw cycles reduced aggregate stability increased erosion/phosphorus loss

21 Runoff, erosion and nutrient loss and climate change Flow deficiency, difference between max and mean ( f(fi))

22 Runoff, erosion and nutrient loss and climate change Runoff is generating erosion In this case USLE not applicable. An option is using a MUSLE - like equation in which rainfall energy is replaced by runoff energy In USLE R Obtained from Q max -Q mean

23 Conclusions Things really happen at the smaller scale, Yearly runoff discharged in relative few days Large differences in average mean daily and maximum discharge depending on scale Large FI values might be influenced by drainage system density Soil type in addition to subsurface drainage systems might play an important role in runoff generation and nutrient t loss processes FI might be an indicator for nutrient loss assessment Nutrient/soil loss might be based on Q max -Q mean relation in addition to MUSLE- like approach

24 Thank you for your attention