Developing optimum subsurface drainage design procedures

Figures & data

Figure 1. Occurrence of Webster soil by county, in southern Minnesota.

Figure 2. Input screen for spreadsheet design tool.

Table 1. Primary DRAINMOD outputs for the Webster soil with various drain spacings and depths.

		Drainage spacing (m)
Drain depth (cm)	UD	46	40	35	29	23
Relative crop yield
90	42.6	83.2	86.1	89.7	93.1	95.9
105	42.6	89.8	92.0	94.5	96.5	97.9
120	42.6	93.4	94.9	96.6	97.9	98.8
135	42.6	95.8	96.9	98.1	98.8	99.2
Internal rate of return (%)
90		1.45	1.46	1.43	1.37	1.26
105		1.67	1.64	1.56	1.45	1.29
120		1.78	1.72	1.61	1.47	1.30
135		1.84	1.77	1.64	1.48	1.29
Mean annual drainage volume (cm)
90	0.0	12.4	12.7	13.2	13.8	14.1
105	0.0	12.9	13.2	13.6	14.1	14.6
120	0.0	13.5	13.7	14.0	14.3	14.8
135	0.0	13.9	14.0	14.4	14.7	15.1
Mean annual surface runoff (cm)
90	15.0	3.6	3.4	3.1	2.8	2.8
105	15.0	3.0	2.9	2.6	2.4	2.1
120	15.0	2.5	2.3	2.2	2.0	1.8
135	15.0	2.0	1.9	1.7	1.6	1.5

UD = undrained.

Table 2. Four performance indices for the Webster soil with various drain spacings and depths.

		Drainage spacing (m)
Drain depth (cm)	UD	46	40	35	29	23
Crop yield index
90		1.00	1.07	1.16	1.24	1.31
105		1.16	1.22	1.28	1.33	1.36
120		1.25	1.29	1.33	1.36	1.38
135		1.31	1.34	1.37	1.38	1.39
Profitability index
90		1.15	1.16	1.14	1.09	1.00
105		1.29	1.27	1.21	1.12	1.00
120		1.37	1.33	1.25	1.14	1.00
135		1.42	1.37	1.27	1.14	1.00
Drainage volume index
90	0.0	1.00	1.02	1.06	1.11	1.13
105	0.0	1.04	1.06	1.09	1.13	1.17
120	0.0	1.08	1.10	1.13	1.15	1.19
135	0.0	1.12	1.13	1.16	1.18	1.21
Surface runoff index
90	10.36	2.46	2.34	2.12	1.90	1.90
105	10.36	2.09	1.99	1.81	1.62	1.47
120	10.36	1.69	1.61	1.48	1.40	1.25
135	10.36	1.39	1.33	1.19	1.08	1.00

UD = undrained.

Figure 3. Performance indices for the Webster soil at Waseca, Minnesota.

Figure 4. Profitability/drainage index (Index 1) for the Webster soil at Waseca, Minnesota.

Figure 5. Profitability/(Runoff × Drainage) index for the Webster soil at Waseca, Minnesota.