Hydrological consequences of artificial drainage of grassland

Abstract

Soil water regimes and water balances are presented for a series of drained and undrained experimental grassland plots, intended to examine the agronomic consequences of drainage. Although drainage has lowered the watertables and reduced the duration of waterlogging in the drained plots, its effects in terms either of the total water quantities leaving the site or of peak flows is quite small. The major effect of drainage is to alter the route of water loss from the site. In its undrained state, the soil is waterlogged for the majority of the winter, incident rainfall cannot infiltrate, and water leaves as surface runoff or near-surface flow. The introduction of fissures by mole drainage both provides an outlet and enhances the macroporosity, so that the rain moves rapidly through the soil and appears as drainflow. Consequently, the additional delay in generating peak runoff through the drainage system is only of the order of 30 minutes on this site.

Runoff formation from experimental plot, field, to small catchment scales in agricultural North Huaihe River Plain, China

“…Groundwater maintains a basic flow and feeds additional water to the ditch (Bouzigues et al, 1997). With the introduction of ditches or underground drainage, subsurface flow has a greater control in storm runoff for an agricultural catchment (DeWalle and Pionke, 1994;Wesström et al, 2003;Armstrong and Garwood, 1991;Cey et al, 1998;Burt and Slattery, 2006).…”

Short-term changes in δ13C and δ15N signatures of water discharged from grazed grasslands

“…In both cases, these variations were strongly correlated with FLOW (MND, r = À0.87; P = 0.0003: ZND, r = À0.75; P = 0.005), with 13 C enrichment decreasing with increasing FLOW. As microbial transformation of organic residues tends to increase 13 C enrichment of the remaining material, it appears that an increasing proportion of less transformed organic matter was exported as rates of discharge from the drained plots increased with the intensity of the storm. As d…”

“…The dried samples thus obtained from the undrained plots were light brown in colour and of low density, whereas samples from the drained plots were dark brown and of higher density. Samples were weighed into tin capsules and analysed for 13 C and 15 N natural abundance using an ANCA/SL 20/20 continuous flow isotope ratio mass spectrometer (IRMS) (Europa Scientific Ltd., Crewe, UK).…”

“…For details of soil properties see Scholefield et al 12 and Armstrong and Garwood. 13 The complete experiment comprises 14 lysimeter plots of approximately 1 ha, grazed with steers according to grass availability. Seven plots are drained by 55 cm deep mole drains crossing 85 cm deep permanent pipe drains, and are termed drained, while the remaining seven plots, dependent on natural drainage via surface and interflow pathways, are termed undrained.…”

Hydroperiod changes as clues to impacts on Cache River Riparian wetlands

“…The timing and duration of low discharges from the decade of the 1950s to the present are probably increasingly dominated by some hydrologic process operating over a short time period and not by ground-water recharge or discharge from stored water within the basin or wetland. Armstrong and Garwood (1991) described the effects of drainage on runoff characteristics. Although the effects of artificial drainage were found to be quite small, both relative to peak flows and overall water balances, the major effect of drainage is to alter the route of water movement throughout the site, affecting both agricultural and nitrogen balance.…”