The research of the draining surface water from drained areas has become relevant with an increase of drainage system areas. In order to maintain sufficient drainage efficiency by the draining surface water from the drained fields the density of open inlets for the surface water had to be increased to 5.5 u 100 haE-1. That was determined by the density decline of the open ditches. The observations of the technical condition of open inlets for the surface water in the drained fields of the country have been performed since 1986. It was established that prevalent type of the inlets is F-5 design. Such inlets amounts over 90% of all tested ones. The article discusses the condition of the inlets of such type, evaluates the selection of the installation location, conditions of surface water running to an inlet and the condition of water inlet openings. The research demonstrated some disadvantages of inlet designs, quite a few mistakes of installation and breakdowns during operation. A clear increasing tendency of water inlet openings being blocked by the ground and vegetation was established: in 1986 11.1% of water inlet openings were completely blocked, in 1996 the percentage was 20.8% and in 2007 it was 42.9%. On the basis of this it can be stated that the inlets with halfway blocked openings will stop functioning soon as well if the maintenance work is not carried out in good time and an appropriate way.

Both forestry theory and practice have proved that amelioration favours the growth of forest stands significantly. The growing stock increases even 10 times, if the amelioration system is well-functioning. Joint Stock Company Latvia State Forests that is managing half of forests in Latvia has started renovation of old amelioration systems aiming to improve the productivity of state owned forests in Latvia. In order to evaluate the impact of the renovation of the old amelioration systems, a tree ring width in 7 pine stands, 5 spruce stands and 3 birch stands was analysed. This study shows that the renovation itself has not affected the productivity of mature pine, spruce and birch significantly 3-4 years after the renovation. Authors have come to a conclusion that the reason for that could be too short observation period or particularities of a stand structure and age.

The investigations were carried out in the Lithuanian Agricultural University Water Research Institute land plots in the Endocalcari Endohypogleyic Cambisols (CMg-n-w-can). The basis of the investigation is 3 variants field experiment. Each variant consists of 3 in 0.54 ha drainage. The traditional arable farming is applied in variant I. In the variant II the land is not being cultivated, but in spring the perennial ryegrass (‘Lolium perenne L’) is being seeded into the spring barley and kept till spring. In the variant III the land is not being cultivated after the harvest and left for the rest till spring. The variant II is distinguished by the minimal mineral nitrogen content. Applied to cultivated and uncultivated land, the min N reserves are increased 51 - 83 and 33 - 40 and 11 - 101 and (38 - 134%) (to 9.5 - 14.3 mg kgE-1 and 152 - 68 and 154 - 61 kg haE-1). The average investigation of N concentration in the drainage water shows, that the minimum concentration of this element was in the second variant. Applied to the traditional farming and uncultivated land, the N concentration is increased by (30 - 42% to 34 and 37 mg lE-1). By average data the min N, leaching by drainage water in the variant II was minimal and about 27 kg haE-1. Applied to the arable farming and uncultivated land, the min N leching is increased (30 - 55%) (to 35 - 42 kg haE-1).

The establishment, maintenance and renovation of forest drainage systems are carried out to ensure the development of high quality forest stands and to secure access to forest resources, but it also poses a risk of erosion and increased discharge of suspended solids and nutrients associated with it. The aim of the study was to analyse the efficiency of standard-sized sedimentation ponds built by JSC ‘Latvia’s State Forests’ for sediment and nutrient retention during and after drainage network maintenance. To assess the efficiency of standard-sized sedimentation ponds six study sites were established and various chemical and physical parameters were measured for three years to evaluate water quality and to estimate runoff of plant nutrients and suspended solids. Sampling was carried out before and during drainage network maintenance and during two years following it. Despite the fact that some effect in reducing suspended solid export from catchments was observed, the results revealed insufficient efficiency of the sedimentation ponds in retaining plant nutrients and eroded matter during and after the drainage network maintenance. Retention of Ntot, N-NO3 sup(-) , P-PO4 sup(3-), N-NH4 sup(+) and DOC was ambiguous. It was concluded that other water protection structures should be considered or different parameters of sedimentation ponds should be used to improve the water quality exiting the drainage systems and entering waterbodies.

Establishment of sedimentation ponds is a method to reduce the negative impact of forest management (fellings, drainage) on the quality of nearby rivers, lakes and streams. The aim of the study was to determine the efficiency of sedimentation ponds in forest drainage systems during high precipitation periods. Nine sedimentation ponds with different drainage areas were analysed. The sedimentation ponds are located in the northern part of Latvia on different types of soils and managed by the Joint Stock Company ‘Latvia’s State Forests’. In order to determine efficiency of these ponds the following parameters in water samples were measured: nitrate (NO3 -), ammonium (NH4 +), phosphate ion (PO4 3-), total nitrogen and total suspended solid concentration. The amount of precipitation was taken into account. Results show that there is a correlation between the amount of precipitation and concentrations of total suspended solids and total nitrogen. Ammonium ion concentration was the only parameter that significantly exceeded water quality standards in Latvia. Only one of the objects had high concentration of pollutants, which could be explained with the peaty soil of its drainage area. In further studies data should be collected more frequently, three or four days during one precipitation period.

Drainage ensures flow of water and access of oxygen to the roots of the trees. Therefore, melioration systems have been established in a third of the forest area of Latvia, and for the most part highly productive stands can be observed in these areas. Water flow in these systems is often stopped by beaver dams. The aim of our case study was to assess the impact of ditch reconstruction on the increment of the coniferous trees. Increment cores were collected from 169 trees at a distance up to 45 m from the ditch in the drainage system that was reconstructed 8 years prior. Drainage system reconstruction reversed the trend of declining radial increment for both Scots pine and Norway spruce; however, the influence of this measure over an 8 year period was statistically significant, notable (55%) and positive only for Norway spruce, growing closest to the edge of the ditch. Other growth limiting factors need to be considered and tackled to ensure the highest effect of the investment in drainage system reconstruction, including choice of the tree species, stand density, age, and availability of nutrients.

The paper presents the study material and analysis of the distribution of woody vegetation of regulated streams in southeast Lithuania. The studies were carried out in 110 randomly selected slope strips of regulated streams in the Neris River basin in the Baltic Highland within the period of 2005 to 2006. During the studies 32 species of woody vegetation were found, from which 14 species of trees and 18 species of bushes. In regulated streams different species of willows are most common. However their distribution on channel slopes is different. For most species of woody vegetation the conditions are most favourable in the lower and middle part of slopes. Here their density is highest (0.34 +- 0.89 and 0.73 +- 0.139 units mE-2 respectively), the frequency is 0.56 and 0.64 respectively. As it was determined, the frequency of woody vegetation on slope strips of regulated streams is na = 0:61. On the slope the lower overgrowth limit of woody vegetation is ra = 1:58 +- 0:16 m, the upper limit is rv = 4:13 +- 0:22 m. In southeast Lithuania, in discharge network of drainage systems there are more possibilities for planning of ecological means, when trees and bushes are allowed to grow on slopes.

After the private ownership of land was restored and a part of land reclamation structures was given to land owners, the intensity of land use has changed. In the areas of Lithuania, which are less favoured for agriculture, the land is not intensely used. Further financing of land reclamation of such areas from the state budget grants is economically inefficient as the return of relatively high investments is very low. With the changing of land reclamation infrastructure it is necessary to prepare measures which would facilitate rational, regional agricultural specialization corresponding to natural conditions. The routine procedure of financing the land reclamation has to be changed as well. The paper analyses the changes in usage of drained land areas and financing of the land reclamation sector in Lithuania during the last decade (1997-2007). The purpose of this research is to establish the criteria of the economical efficiency of drainage systems and to propose methods how to change the financing of state-owned land reclamation infrastructure. On the grounds of the carried out situation analysis, a methodology of distributing state grants for land reclamation to municipality budgets are presented. To have an efficient use of the state budget funds, the operation and maintenance of shared land reclamation systems have to be carried out according to the maintenance plans approved by municipalities, which would provide for arrangements and compensations due to conflict of interests arising when land plots are used in different ways. Possible ecological measures that could be applied when carrying out repair and reconstruction of drainage systems are discussed.

As the result of the studies on the condition of protective belts of drainage channels (PB) have shown, due to improving maintained and mechanical damaged protective belts large amounts of erosion products contained in surface water inflows the channel bed. Disorderly condition of protective belts does not correspond to the requirements of environment protection. Mechanical damages are often related to unsustainable human activity in the adjacent zone of a drainage channel. According to the principles of soil occurrence in the channel bed, four groups of damages might be distinguished: soil entrance into the channel during the tillage of a protective belt; inflow of washout products from the basin; scours of protective belts and washout of turf flumes of surface water discharge. The most frequent damages enhancing the washout of flumes and inflow of erosion products are total or partial tillage of the protective belt of a drainage channel. From the point of view of erosion process, the inflow of erosion products from the basin is considered as the most dangerous damages, which is inevitable when the width of protective belt is insufficient, particularly in places with deep turf flumes arranged.

The studies were carried out in two control profiles of the Graisupis ditch excavated 40 years ago and situated at the distance of 2.4 and 4.8 km from the outlet in the land of intensive farming in Kedainiai district. The study object contained mineral loam/sandy-loam soils on the flat relief. The areas of catchments in control profiles were 12.1 and 5.9 square km, the largest discharges of spring floods were 3.4 and 1.6 m**3sE-1. Cross-sectional parameters, grass characteristics and flow parameters were measured under the conditions of different discharges (6 replications in each control profile during the vegetation period and 4 replications in spring when the channel bed is clean). As the study results show, roughness coefficient of the grass-cowered channel bed increased up to 21 times, water tables were observed to be 20-40 cm higher, the outlets of the drainage were flooded up. Considering the average grass indices determined in control profiles, grass hydraulic resistance was calculated according to 4 formulas based on the scheme when grass cover resistance is estimated as the total resistance of separate obstructions. The difference of 22.3% between calculated results and natural measurements was determined. The formula estimating grass cover parameters as well as flow regime determined to be most suitable.