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Knowledge of the water level and rate of drawdown is important in water and soil management. Several equations in literature are used to make a relation between soil characteristic, drain information, the declination rate of the water table and other related factors. Almost all of these equations are based on the Bossinesq equation with Dupuit-Forchheimer assumptions. In this study the Bossinesq equation with appropriate initial and boundary conditions was solved numerically to predict a fall in the water table for a level and a bi-level drainage system. Almost identical values of spatial and temporal distribution of water table heights were obtained. In order to compare the capability of both systems, the model was run for a real drainage system project in the Khuzestan region, with a drainage network spacing of 40, 60 and 80(m) in distance. The results show that for a sub-region with 40(m) spacing network, 30 (cm) drawdown in maximum water table elevation (MWTE) takes about 6 and 7 days time in the level and bi-level system, respectively. The same results for a sub-region with 60(m) space is 10.5 and 12 days and those of 80(m) are 12 and 14 days. In additional to the bi-level system with time (Simultaneous falling water table) position of MWTE shifts from the mid- point towards the shallow drain.We conclude that in this spatial project the cost of installation of subsurface drainage system can be reduced about 10.6 percent by using a bi-level system instead of a level system with similar spacing network. Keywords: Numerical methods, Finite Volume, Bi-level drainage

The aims of this study were: 1) to determine the effect of time on the fracture toughness (K[sub iC]), flexural strength (ϭf), and flexural modulus (E[sub f]) of six groups of direct restorative materials including amalgam; and 2) to compare the selected properties of the materials at each time. The null hypotheses tested were: 1) there is no difference between the 1-hour, 1-day, 7-day, 30-day, and 90-day values of each of the K[sub iC], cjf, and E[sub f] for each of the selected materials, and 2) there is no difference between the selected materials with respect to each of their mechanical properties tested at each time. The materials selected for this study were KetacFil (KF, ESPE) - a conventional glass-inomer cement (GIC); PhotacFil (PF; ESPE) - a resin-modified glass ionomer cement (RMGIC); Dyract (Dentsply) and F2000 (3M) - polyacid-modified composite resins (PAMCR) or "compomers"; Z100 (3M) -a hybrid composite resin; Heliomolar (H; Vivadent) - a microfil composite resin; SureFil (SF; Dentsply) and Prodigy Condensable (PC; Kerr) "packable" composite resins; and Valiant PHD XT (V; Ivoclar) - a phase dispersed unicompositional amalgam. Twelve notchless triangular prisms (NTP) (6x6x6x12 mm) and twelve rectangular bars (2x2x25 mm) were made for each test at each time following manufacturers' instructions, and stored in distilled water at 37° C for the duration of the five time intervals before testing. For the K[sub iC] test, the samples were placed in a specimen holder and loaded in tension at a crosshead speed of 0.1 mm/min. The maximum load recorded before crack arrest or complete failure was used to calculate K[sub iC] in MPa*ml/2. The bars were loaded in a three point bending mode and the maximum load recorded at failure was used to calculate df. The modulus was determined from the straight portion of the stress/strain curve. The results were analyzed using a one way ANOVA followed byy Scheffe multiple means comparisons (α=0.05). Based on the limitations of this study and representative materials the results indicate that GICs are the weakest materials and are inferior to RMGIC especially in the short term. RMGICs and PAMCRs are comparable, while both are inferior to CRs and PCRs. PCRs do not show any significant improvement over conventional CRs. Amalgam has the best intrinsic properties over time. The intrinsic properties, K[sub iC] and E[sub f], appear to correlate better with the clinical success of materials than their 07 does.