Tile Drainage: Hydrology and the RRB

Transcription

1 Tile Drainage: Hydrology and the RRB A Presentation of the Tiling and Drainage Workshop August 28-29, 2012 Hankinson, ND Gary R. Sands Professor & Extension Engineer

2 > 21,000 mi of surface drainage works

3 Tile Drainage Hydrology Image Source: Department of Natural Resource Ecology and Management, Iowa State University

4 For Today we re not considering the effects of: Conversion of prairie Surface drainage (ditching) Climate trend/change

5 Q: Can tile drainage affect hydrology & streamflow? A: Of course it can!

6 Q: Do we know precisely what these effects are? A: Not really! A: They could be pos, neg, or neutral

7 Q: Why isn t more known? A: Because hydrology & streamflow depend on many factors!

8 Q: Why isn t more known? A: And these factors continuously change over time and space!

9 Q: So what DO we know? A: We know what factors are important and general relationships

10 Hydrology Precip = ET + Infiltration P=ET+RO+I Image Source: Department of Natural Resource Ecology and Management, Iowa State University

11 Soil is a Key Factor Soil type (fine, coarse)? Cover or crop? Wet?, dry?, frozen? Redistribution

12 Soil is a Key Factor Soil Type Clay Soil? Cover or crop? Wet?, dry?, frozen?

13 Soil is a Key Factor Soil Cover Soil type (fine)? Bare or minimal cover? Wet?, dry?, frozen?

14 Soil is a Key Factor Soil Moisture Soil type (fine)? Bare min cover? Wet conditions?

15 Precipitation Trumps Soil High Precip Intensity? Soil type (fine, coarse)? Cover or crop? Wet?, dry?

16 Gentle Rainfall Event Favors infiltration Tile drainage system influences flow Surface drainage system out of the picture Intense Rainfall Event Favors surface runoff Surface drainage system influences flow Tile drainage system out of picture

17 Q: So what difference does tile drainage make?

18 Effect of Tile Drainage Soil type (fine)? Bare min cover? Wet conditions

19 Effect of Tile Drainage Seepage Seepage Surface Surface Tile ET ET Soil type (fine)? Bare min cover? Wet conditions become drier conditions Q: When would this not be true?

20 BUT

21 Soil & Precip Factors CHANGE WITH TIME & SEASON

22 Changes Over Time & Season Mar Apr May Jun Jul

23 AND

24 Soil and Precip Factors CHANGE OVER SPACE (SCALE)

25 Soil & topo variable Precip variable Distance What else? Drain density

26 Q: Can t we sort out all the factors 1 by 1 and estimate effects on hydrology & streamflow? A: Welcome to the world of computer modeling!

27 100 yr Simulation Crookston, 3 soils, 4 DC DRAINMOD Fargo Soil Undrained 16.8% 2.7% Bearden Soil Undrained 16.5% 2.1% Glyndon Soil Undrained 12.5% 3.5% 82.7% 83.1% 85.3% in/day 5.7% 13.9% 1.4% in/day 5.2% 13.1% 1.5% in/day 9.1% 6.0% 2.2% 81.7% 82.2% 84.3% Drainage Runoff Seepage ET 0.25 in/day 6.8% 13.7% 1.1% 81.2% 0.25 in/day 6.3% 12.7% 1.2% 81.9% 0.25 in/day 10.5% 4.9% 2.0% 84.1% in/day 7.1% 13.7% 1.0% in/day 7.1% 12.3% 1.1% in/day 11.2% 4.8% 1.8% ET ET ET DRAIN RUNOFF 81.0% DRAIN RUNOFF 81.7% DRAIN RUNOFF 83.8% SEEP SEEP SEEP

28 But long term annual averages aren t good enough What about annual hydrology?

29

30 8.0 Annual Drainage Volume (in) y = 0.2x 2.5 R² = Precip = 28 Drainage = 1 Runoff = Annual Precipitation (in)

31 Annual simulated tile drainage, plotted versus precipitation, for Crookston, Annual drainage doesn t correlate well with annual precipitation, and we see many years and a wide range of precipitation values for which no annual tile drainage is predicted. The reason for this poor correlation is that the timing and intensity of precipitation is more important when it some to tile flow, than the annual precip amount. The red colored points are the annual tile flow predicted during 8 of the 13 major flooding years that have occurred since 1990 for the Red River (through 1997). The flow volumes highlighted in the box indicate that in 1997, the model predict that the system would have been dominated by surface flows, and tile drainage would have played a minor role in hydrology. 30

32 But annual numbers aren t good enough either We need to understand hydro on seasonal/daily basis

33 Timing of Ann Peak Flows at Fargo

34 Tile Drainage Seasonality Bearden Soil (0.25 DC, 100 yrs) Drainage 1997 Drain Daily Drainage (in) 1/1 1/31 3/1 3/31 4/30 5/30 6/29 7/29 8/28 9/27 10/27 11/26 12/26

35 The blue dots represent simulated daily tile flow over 100 years. The clustering of the points between March and the end of June illustrate that this is the primary tile flow season. In addition, all the largest daily tile flows occur in this part of the year. The purple line is the daily tile flow for the 1997 season, indicating that the tile flow peak occurred well after the flooding season, where flows were dominated by surface runoff (not tile flow). 34

36 Tile Drainage Seasonality Bearden Soil (0.25 DC, 100 yrs) RO Drain RO UD Daily Surface Runoff (in) 1/1 1/31 3/1 3/31 4/30 5/30 6/29 7/29 8/28 9/27 10/27 11/26 12/26

37 Here we have simulated daily surface runoff, under both drained (orange), and undrained (red) conditions. We find that beginning in June or so, the runoff values for both drained and undrained conditions are aligned, indicating that the tile system is basically out of the picture at this point in the growing season. Earlier in the growing season, we see that on many occasions, the undrained surface runoff values exceed those of the drained conditions, illustrating that tile drainage tends to reduce surface runoff and increase infiltration. 35

38 Bearden Soil (Mar Dec, 1997) Water Table Depth from Surface (in) D = 0.25 RO-D = 0 RO-UD = 0.3 D = 0.8 RO-D = 1.8 RO-UD = 2.35 WT UD WT D WT CD Drain Drain CD Drainage (in) /25 4/24 5/24 6/23 7/23 8/22 9/21 10/21 11/20 12/

39 In this slide we show the predicted water table depths and tile flow for 1997, to illustrate the differences in hydrology between drained and undrained conditions (the gray dotted line indicates the tile depth of 3.5 ft, for these simulations). The undrained water table (blue) rises quickly to the surface and remains there through the flooding season, and returns to the surface in late June. The drained water table (amber) remains well below the surface, but rises above the tile and produces drainage from late April to late May. The tile flow (read from the upper axis) for 1997 shows a smaller flow volume during flooding season and a larger spike in late June, early July. The flow volumes shown in the boxes for the two events indicate reduced surface runoff with the tile drained conditions. 39

40 Tile drainage hydrology relationship is complex and involves many factors: Soil & precip conditions VERY important Precip can trump soil (or vice versa, for frozen soil) Everything changes in TIME & SPACE General cause effect statements unrealistic Large scale effects unknown most work at field scale Studies suggest tiling may reduce surface runoff and increase infiltration Modeling studies suggest overall water yield may increase with tiling Surface flows may dominate in major flooding years We will have to be comfortable with probability basis

41 THANK YOU!