On-farm water resources management: an approach to optimize regional hydrology

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1 Agricultural Effects on Ground and Surface Waters: Research at the Edge of Science and Society (Proceedings ol'a symposium held al Wageningen. October 2000). I Ai IS Publ. no On-farm water resources management: an approach to optimize regional hydrology J. R. HOEKSTRA Centre for Agriculture and Environment, PO Box 10015, 3505 A A Utrecht, The Netherlands. rhoekstra@clm.nl J. M. P. M. PEERBOOM Peel and Maasvallei Water Board. PO Box 3390, Venlo, The Netherlands Abstract In the Mariapeel nature reserve the groundwater level has fallen dramatically. In the surrounding agricultural area, the groundwater level is low, which results in a loss of groundwater resources from the nature reserve. This affects biodiversity in a negative way. Optimizing regional hydrological management, with an emphasis on raising groundwater levels, can improve the coexistence of agriculture and nature. This is an important issue in recent- Dutch water management. Within the nature reserve, several measures have been taken to stop the desiccation. The surface water levels have been raised, a finer pattern of compartments has been introduced and several ditches have been dammed. However, this approach is not enough to ensure that groundwater levels remain high in summer. Additionally, measures in the surrounding area must be taken. In this study, we examined the ways by which the 17 fanners in the surrounding area can contribute to a better hydrological situation in Mariapeel, by taking on-farm measures. In an intensive process the possibilities and their consequences for hydrology and farm management were worked out. Then, in a hydrological study, the regional hydrological effects of various approaches to water management were compared. This study proves that water management at the farm level can improve regional hydrology. Active participation of farmers is necessary to find effective measures. It is desirable to give farmers responsibility for managing water resources at the local scale. Close cooperation between water boards and local farmers is necessary. Regional agreements are appropriate policy instruments to set down responsibilities of farmers and authorities. Key words eco-hydrology; farmer cooperation: groundwater levels; on-farm measures; peatland; regional hydrological management; The Netherlands INTRODUCTION Mariapeel is a nature reserve of more than 1000 ha in the Dutch province of Limburg. It is one of the few relatively large remnants of old peatland in The Netherlands. In the past decades, the groundwater levels in this nature reserve have fallen dramatically. The causes can be found in the internal hydrology of the nature reserve, as well as in the hydrology of the surrounding agricultural area. The main causes of groundwater depletion in the nature reserve are: sub-optimal water management, the reduction of the peat-layer by oxidation and excavation, and the increase of évapotranspiration due to woodland regeneration. The main causes in the surrounding area are the deep drainage and the extraction of groundwater for agricultural purposes. The hydrological

2 240 J. R. Hoekstra & J. M. P. M. Peerboom situation leads to a groundwater outflow from the Mariapeel to the surrounding area, and causes a degeneration of the natural values. In order to improve the conditions for nature, the local water board Peel and Maasvallei is trying to find ways to optimize the regional hydrology in cooperation with other regional authorities and local farmers. Optimizing regional hydrology Because of its great ecological importance and natural value, a hydrological protection zone has been created around the Mariapeel. One of the consequences is that within the buffer zone no activities are allowed which can influence the nature reserve in a negative way. For example, the regional authorities can prevent the increase of pipedrainage and groundwater withdrawal for irrigation. A hydrological buffer zone was estimated in 1993 and later (in a more detailed study) in 1998 (Oranjewoud, 1993, 1995). The definite border of the buffer zone ranges between 1 and 3 km from the border of the nature reserve. To raise the groundwater level, measures can be taken within the nature reserve and in the hydrological buffer zone. Within Mariapeel, the restoration has focused on the prevention of runoff and outflow of infiltrating rainwater from the nature reserve to its surroundings. These measures were very effective: they caused a rise of the groundwater level of more than 1 m within the nature reserve. In the hydrological protection zone, the policy has not been very successfully. It proved to be difficult to take measures like decreasing drainage or reducing groundwater withdrawal for sprinkler irrigation, because they restrict farming practice. Therefore, the local farmers, the water board and the province of Limburg decided to investigate policy alternatives that should have a similar or even greater effect on the protection of Mariapeel. To investigate the alternatives, a project was initiated with two parts: 1. "Farmers with water", addressing following question: Which on-farm measures can be taken to contribute to the hydrological restoration of the nature reserve? This project concentrated on 17 farms and was executed by the Centre for Agriculture and Environment in 1998 (Bleumink et ai, 1998). 2. A hydrological model study to show the hydrological effects of on-farm and regional measures and to quantify the benefits and costs. The model study concentrates on the total hydrological protection zone around Mariapeel and was executed by Grontmij in 1999 (Grontmij, 2000). On-farm water resources management The study area for the on-farm management study is called Evertsoord (224 ha) and consists of 14 long fields aligned perpendicular to the Mariapeel. Evertsoord is former peatland that has been cultivated since between 1930 and In a short period it has been transformed from a relatively wet area into well-drained agricultural land used for dairy farming, arable crops, vegetables and horticulture. In the Evertsoord study area there are 17 farms, of which eight are pig farms. The livestock density leads to high levels of manure production and the need to spread slurry early in the season.

3 On-farm water resource management: an approach to optimize regional hydrology 241 The hydro-logical structure consists of a network of deep ditches, channels and a drainage system. To avoid drought, almost all the farmers irrigate their land by sprinkling with mm groundwater each year. Drinking water for livestock, and water for flushing and cleaning livestock sheds and washing machinery, accounts for 2100 m J per fanner per year, of which 450 m 3 is extracted from the groundwater. In order to find innovative ways for on-farm water resources management, we set up a close cooperation with 17 farmers. From the beginning of the project, we involved their ideas. Because these fanners experience drought damage on their farms, they were interested in participating in the project. In two regional meetings we initiated the project by giving information about the hydrological characteristics of Mariapeel and the surrounding area, and the influence of fanning practice on the nature reserve. We visited the 17 farms individually to gather detailed information about water use, sprinkling and mineral management. In the farm visits, we discussed a long list of onfann measures. We evaluated the expected effects, the practical consequences and their incorporation into the farm management system. With this information, we composed 17 Farm Water Plans in which we gave a description of the on-farm measures. We analysed the effectiveness and practical and financial consequences for farm management. Each Farm Water Plan contains three packages of measures: a basic, a plus and a maximum package. In a regional workshop we discussed the perspectives of on-farm water management with the fanners and representatives of the water board. In Table 1 a summary of the on-farm measures in the three packages is given. The basic package contains measures that can easily be incorporated into the farm management without financial loss. In the fields, the groundwater levels are raised in order to optimize water supply for crop growth. These measures reduce drought damage (if sufficient water is available) without negative effects. The plus package contains measures that require investments but do not have significant consequences for the overall structure of the farm. Technical measures allow the farmers to raise the weirs in the field ditches. A "composite drainage system" permits high water levels in the ditches while maintaining optimal groundwater levels in the fields. With rainwater basins, the use of purified wastewater and optimization of sprinkler inigation, the use of groundwater is significantly reduced. In the maximum package, the measures require substantial investment and lead to structural changes in the farm management system. Fanners raise the surface water in their ditches to a level such that 20% of the grassland suffers from water excess damage. The conditions are sub-optimal for arable crops that require well-drained soils. Regional hydrology study To investigate the hydrological effects of the on-farm measures, we used the integrated hydrological model SIMGRO (Quemer & van Bakel, 1989), which had already been used to detennine the hydrological protection zone. It is an integrated non-steady groundwater-surface water model with a very well developed algorithm for interaction between ground and surface water. We calibrated the model on a large groundwater data set of 10 years. We studied the following aspects: surface water level management and water conservation in the secondary and the primary watercourses, artificial water

4 242 J. R. Hoekstra &J.M.P. M. Peerboom Table 1 On-farm measures to improve the regional hydrology of Mariapeel and surrounding agricultural areas. Measures for on-farm water resources management Basic Plus Max. package package package Drainage More small weirs for water conservation Shallow ditches and field-drains Improvement of the soil structure Create smooth soil surfaces + + Improvement of the deep soil structure + + Improve the spatial distribution of ditches + + Use shallow and compound drainpipe systems + + Provide financial compensation for water damage + Compensate water damage with extra hectares + Sell low-productive agricultural fields + Remove intensive crops to other fields + Sprinkling Calculate the profits of sprinkling Technically optimize the sprinkling equipment Use a sprinkling advice system No sprinkling in stormy conditions Invest in technically optimal sprinkling equipment + + Use computer-controlled systems + + Optimize spatial distribution of groundwater wells + + Use rainwater basins for vegetable-growing + + External water supply + Cultivate alternative crops + Reduce or stop sprinkling + Buy roughage to compensate lower yields + Use a large rainwater basin for all arable crops + Farm water-use Analyse farm water-use and compare with standards Reduce water losses Use best technical means on the farm Create a water purification system (helophytes) + + Use purified rainwater for farm water + + supply from the River Meuse, increasing surface water levels in combination with additional pipe-drainage, etc. We calculated the rise of the groundwater table during winter and summer in the nature reserve Mariapeel and the surrounding area. The predicted changes in groundwater levels were used to calculate the possible agricultural damage with the HELP-method. The hydrological benefits for the nature reserve were calculated on the basis of known groundwater duration lines for the characteristic natural vegetation in Mariapeel. Using the results of Fanners with Water, we composed four scenarios. In scenarios 1 and 2 the on-farm measures from the basic package are involved. Scenario 3 is more or less comparable with the plus package and scenario 4 with the maximum package. In scenarios 3 and 4 we also included additional water supply in dry periods, even in the smallest watercourses:

5 On-farm water resource management: an approach to optimize regional hydrology Basic package, modern farmer friendly water conservation: - water conservation in all watercourses, - groundwater guided surface water level management, - pipe drainage and irrigation if necessary, - no increase of artificial water supply. 2. Basic package, traditional farmer friendly water conservation: as scenario 1, plus: - traditional water level management with fixed summer and winter surface water levels. 3. Plus package, optimal water management: as scenario 1, plus: - additional water supply in all water courses if necessary. 4. Maximum package, nature friendly water management: as scenario 1, plus: - water levels only suitable for grassland cultivation, - prohibition of all pipe-drainage and groundwater withdrawal, - additional water supply in all watercourses if necessary. RESULTS In Table 2 a summary of the calculations of the final scenarios is given. The main conclusion is that the voluntary water conservation measures are more effective than prohibiting irrigation during summer. Prohibition of irrigation will lead to a water table rise of 5 cm in the nature reserve Mariapeel, while even the most farmer friendly scenarios, 1 and 2, will lead to a rise of more than 10 cm. The difference between the effects of water conservation in comparison with the effects of prohibition of pipedrainage is even greater. Prohibition of pipe-drainage in the whole protection zone will lead to a 1-5 cm maximum rise of groundwater level at the edges of the reserve (Oranjewoud, 1988). Even pipe-drainage in combination with water conservation can have a positive effect on the resulting groundwater levels, as fanners can take more risks with their conservation strategy because they can discharge any surplus drainage water quickly. The model results show clearly that the greatest effects will be expected in summer periods. The effects of "groundwater guided water management" (scenario 1) are limited in comparison with the traditional water management (scenario 2): a maximal 2 cm rise in summer within the nature reserve. Also the effects of artificial water supply from the River Meuse are limited; this will raise the groundwater level within the nature reserve by only 2 cm (scenario 3 compared to 1). Scenario 4 leads to the highest groundwater rise in the reserve: 20 cm in summer. Financial consequences of on-farm water management Many of the measures reduce drought damage in the growing season and reduce the costs for irrigation. In particular, the measures in the plus package leads to higher yields. These savings can amount to 180 euro ha" 1 for grassland, 36 euro ha" 1 for maize

6 244 J. R. Hoekstra & J. M. P. M. Peerboom Table 2 Summary of the results of the hydrological study. Raising the groundwater level in the nature reserve and the surrounding agricultural area. Averages for winter and summer periods. Scenario Rise of groundwater level in Rise of groundwater level in the agricultural area: the nature reserve: Winter (cm) Summer (cm) Winter (cm) Summer (cm) Voluntary on-farm measures 1. Modern farmer friendly Traditional farmer friendly Optimal water management Nature friendly Measures forced by legislation Prohibition of irrigation nil 5 Prohibition of pipe drainage max 1-5 nil and 390 euro ha" for asparagus. Economic benefits must be carefully weighed against the investments for the optimization of hydrology. The maximum package has significant consequences for intensive arable farming. The farmers have to alter their cropping plans dramatically and have to change to cereals, triticale and other alternative crops. Dairy farming remains profitable with the maximum package, but the farmers will have to change their farming management to deal with variable groundwater levels. Water conservation in the smaller watercourses by placing small weirs, will cost euros for every farm covering about 30 ha. For the whole hydrological protection area around Mariapeel, this would mean an investment of about euros to complete the measures. Scenarios 3 and 4, with additional water supply will cost about 20-40% more because of the additional technical investment in the watercourses. The management costs of the four scenarios will vary a lot. DISCUSSION In this study we have investigated innovative ways for on-farm water resource management. We involved the knowledge and experience of the local farmers from the beginning of the project. We invested much time in the cooperation process. Representatives of local farmers' organizations played an important role at the start of the project. To discuss the future perspectives of on-farm water management, close cooperation between the water board and the local farmers is essential. Little is known about the regional hydrological effects of small-scale on-farm measures (Table 1). In order to test the hydrological effects of on-farm measures, fieldexperiments on a small scale are desirable. The effects of on-farm measures in the surrounding area are relatively small in comparison with the effects of the measures already taken inside the nature reserve, which caused a groundwater rise of more than one metre. To obtain insight in to the hydrological and financial effects of both on-farm measures and measures at a regional scale, it is necessary to perform a study such as

7 On-farm water resource management: an approach to optimize regional hydrology 245 described here. However, the costs of a hydrological study are relatively high. It is not possible to undertake expensive research in all regions where water conservation is desired. In this study, the financial consequences could not be calculated in detail. For calculating the target level for the weirs it was not clear whether water was available or not during the growing season. A hydrological study with more detailed data could provide an answer to this question. In this study, we focussed on water resources management. In modern water management however, measures to improve water resources and water quality management should be integrated. The farm level is the proper scale to consider both water resources and quality management. In particular the environmental effects of the application of nutrients and pesticides should be integrated in such a project. Farmers can play an active role in regional water resource management. In the first place they can apply on-farm measures that have a positive effect on regional hydrology. In the second place they can be given responsibility for detailed water resource management. In close cooperation with the water board, farmers can play a role in controlling water resources on a field scale, in optimizing surface water levels and in monitoring the effects. The responsibilities of farmers and the water board can be set down in regional agreements. These should include the on-farm measures, the control over surface water levels in the ditches, costs and the monitoring of effects. This study showed that the participation of farmers is very important to get insight to the on-farm measures. However, the participation of fanners in the hydrological study is difficult because there is a great gap in hydrological knowledge between farmers and researchers. As a follow-up to this study, the water board has developed a course: Water Management for Farmers. CONCLUSIONS On-farm water resources management is a successful approach to optimizing regional hydrology. In the area surrounding a nature reserve, farmers can contribute in a positive way to the rise of the groundwater level in the nature reserve. The most effective measures were the introduction of water conservation weirs in the smallest watercourses. Active participation of farmers is necessary to find effective measures that do not restrict farming practices. It is desirable to give farmers a responsibility for managing water resources at the local scale. There are many examples of on-farm measures. Some of them require financial investments, but others can benefit farming practice, e.g. measures that avoid drought damage. In the Mariapeel study area, on-fann water resources management has significant hydrological effects on the groundwater level in the nature reserve. Compared to measures enforced by legislation, voluntary on-farm measures proved to be more effective. To study on-farm water management, close cooperation between the water board and local farmers is essential. The knowledge and ideas of the farmers must be involved from the beginning of the project. Regional agreements are the proper policy instruments to set down responsibilities of farmers and authorities.

8 246 J. R. Hoekstra &J.M.P.M. Peerboom REFERENCES Bleumink, J. A., Boland, D. & Buys, J. C. (1998) Boeren met wafer in de Mariapeel (Farmers with water around Mariapeel, an approach to prevent nature from desiccation) (in Dutch). Centre for Agriculture and Environment, Utrecht, The Netherlands. Grontmij (2000) Stappenplan Hydrologie Mariapeel, rapport van het hydrologisehe onderzoek (Step plan l-lydrology Mariapeel: report of the hydrological research in the Mariapeel Region) (in Dutch). Grontmij Water. I loutcn (in preparation). Oranjewoud (1993) Eco-hydrologisch onderzoek Mariapeel-Deiirnesepeel (Eco-hydrological research of the Mariapeei/Deurnesepeel-region) (in Dutch). Oranjewoud BV, Oosterhoul, The Netherlands. Oranjewoud (1998) Hydrologisehe beïnvloedingszone random Mariapeel en Grcunvveen (Hydrological protection zone around the Mariapeel and Grauwveen) (in Dutch). Oranjewoud BV, Oosterhout, The Netherlands. Querner, li. P. & van Bakcl, P..1. T. (1989) Description of the Regional Groundwater Flow Model SIMGRO. Report 7, DLO Winand Staring Centre, Wageningen, The Netherlands. Workgroup 1 lelp-tablcs ( 1987) De imioed van de waterhuishouding op de landhomvkundigcproductie (The influence of the hydrological situation on agricultural production) (in Dutch). Landinrichtingsdienst, Utrecht, The Netherlands.