C.W.J. (Koen) Roest[2]



1                    The issue

Traditionally, land drainage is a tool to improve crop growth conditions for agriculture. This is done through optimising crop root zone soil moisture conditions to prevent crop damage. By removing excess water from the crop root zone, water-soluble constituents are removed as well. Solute removal may be beneficial for the crops grown (removal of salts), non-beneficial for the crop (leaching of nutrients) or resulting in negative impacts elsewhere (transport of agro-chemicals).


When examining drainage as a tool for integrated water management we have to consider effects of drainage on other functions of the land as well. These other functions should not be restricted to the agricultural fields where drainage is practised, but also neighbouring field influenced by drainage or downstream areas where the effluent is used as water source.


2                    Drainage in the context of integrated water management

Improving land drainage conditions locally, to improve crop production, does not necessarily mean that interests of other actors and stakeholders in the region are safeguarded. On the contrary, if those interests are not considered during drainage implementation, it is more likely that these interests will be damaged.


Based on the above considerations, this leads us to the conclusion that the benefits of land drainage for agriculture should be weighted against the interests of other actors and stakeholders.


3                    Solute transport

Based on the assigned subtopic, we should discuss the influence of solute transport by drainage in the framework of integrated water management. Discussing solute transport, we can approach the issues from two sides. The conventional approach is to look at adverse impacts of solute transport, which need to be mitigated or at least addressed to fit in the integrated water management concept. An alternative approach could be to discuss (potential) positive effects of drainage induced solute transport processes (the other side of the same coin).


4                    Drainage to change the pathways of solutes

By land drainage the pathway of soil water fluxes changes. A deeper groundwater table may reduce surface run-off and thereby reduce phosphorous leaching to surface waters. A shallow groundwater table may promote denitrification processes in the soil and reduce nitrogen leaching to surface waters. I would like to open the discussion (case studies, experience, and thoughts) on this subject.


5                    Purification of water through drainage

Polluted water streams may be cleaned by treatment in wetlands or by passage through the soil system.  Drainage is part of such cleaning activities and recovers the cleaned water resource. I would like to open the discussion (case studies, experience, and thoughts) on this subject.


6                    Other examples

Any other examples of drainage as a tool for integrated water management are welcomed here. Please submit your case studies, experience or thoughts on this subject.


[1]         Paper No 049 (Discussion Paper). Presented at the 9th International Drainage Workshop, September 10 13, 2003, Utrecht, The Netherlands.

[2]         Senior Scientist, Alterra, Wageningen, The Netherlands.