GEOL 4220Exam # 2 Study GuideLecture 1 (Flow Net Analysis)1)Flow Nets – a simple visual method of capturing the major elements of a groundwater flow system is to use flow nets. a. A qualitative model of a flow system 2)Equipotential lines – lines of equal hydraulic head3)Flow lines – imaginary lines that trace the path of a groundwater molecule as it flows through an aquifer a. Flow lines cross equipotential lines b. In an isotropic aquifer, the flow lines will cross the equipotential lines at right anglesi. Isotropic – hydraulic property is the same in all directions ii. In this case, isotropy means that’s the groundwater flow is in the directions of the steepest hydraulic gradient c. In an anisotropic aquifer, the flow lines may cross the equipotential lines at angles other than 90 degreesi. Anisotropic – hydraulic property is different in all direction ii. In this case, hydraulic conductivity may be highest in a direction that is not the steepest gradient – cannot have a flow net d. Flow lines tend to diverge from recharge areas and converge to discharge areas 4)Assumptions:a. The aquifer is homogenous and isotropic b. The aquifer is fully saturated i. Cannot occur in the unsaturated (vadose) zone c. There in no change in the potential field over time – steady stated. The soil and water are incompressible i. There is no storage e. Darcy’s law applies (laminar flow)5)Boundaries:a. Constant head boundary i. Flow lines intersect constant head boundaries at right anglesii. Example: a lake is at the surfaceiii. Boundary is equipotential line iv. Illustrated by the water level boundary in the picture belowb. Impermeable boundaryi. Confining layer is the boundary – no flow 1. Example: clay or bedrockii. Can be above or belowiii. Flow lines run parallel to the boundary and equipotential lines will cross the boundary at right anglesiv. Opposite of constant head boundaryv. Illustrated by the impervious stratum boundary in the picture belowc. Water table boundaryi. For unconfined aquifersii. The water table is neither a flow line nor an equipotential lineiii. It is just a surface where the head is known 6)Rules:a. Flow lines and equipotential lines are always perpendicular and cross at right anglesi. Same squares are used everywhereb. Equipotential lines are always perpendicular to no flow boundariesc. Equipotential lines are always parallel to constant head boundaries b/c these boundaries are themselves equipotential lines d. Flow lines can never intersect 7)To calculate:a. (Higher head – lower head)/ amount of equipotential lines = flow b. Amount of equipotential lines can also be the amount of boxes minus oneLecture 2 (Streamlines/Capture Zones)1)Recharge area – topographic highs where groundwater flows downward away from the water table2)Discharge area – topographic lows where the groundwater moves upward with respect to the water table3)Local flow system develops between a topographic high (recharge area) and an adjacent topographic low (discharge area). 4)Intermediate flow system consists of several topographic lows intervening between recharge and discharge areas. 5)Regional flow system has its recharge area at the highest part of the groundwater basin and its discharge area at the lowest part of the basin 6)Stagnation point develops between two flow systems with equal flow magnitudes but opposite flow directions.a. If the stagnation point is up gradient you have a recharge areab. If the stagnations point is down gradient you have a discharge area 7)Under pumping condition, normal groundwater flow path directions change in response to changes in the water table gradient.a. This can occur because of pumping groundwater from a wellb. Water levels decline – drawdown i. Most declination occurs in soils closest to the well 8)Cone of depression – unequal changes in water levels from pumping, creating a cone like depression in the water table around the pumping well.a. Drawdown – amount of decline in the cone of depression b. Unconfined aquifer (water table) - actual depression of water levelsc. Confined aquifer – a reduction in the pressure head surrounding the pumped well 9)Stagnation point – point at which cone of depression returns back to normal water table height a. Flow is in opposite directions at stagnation point b. If the stagnation point is up gradient you have a recharge areac. If the stagnations point is down gradient you have a discharge area 10) Capture zone – area of water around a well that flows into that wella. Larger on down gradient side of well 11) Factors effecting the cone of depressiona. Pumping rate of the wellb. Type of aquifer materialc. Amount of water stored in the well d. Thickness of the aquifer12) Equilibrium – equilibrium occurs in the cone of depression when the amount of water released from storage equals the rate of pumping Lecture 3 (Well Hydraulics)1)Well hydraulics – the response of an aquifer to a pumping well 2)Aquifer tests – a well is pumped and the rate of decline of the water level in nearby observation wells is recordeda. Time drawdown data us used to derive hydraulic parameters of the aquifer3)Assumptions for pumping:a. The pumping well and all observation wells are screened only in the aquifer being testedb. The pumping well and the observation wells are screened throughout he entire thickness of the aquifer i. Screen – a filtering device that allows water to enter the well without unconsolidated material4)Steady state conditionsa. Well is pumped for a long time so there is no more draw down over time b. Recharge rate equals pumping c. Aquifer is homogenous and isotropicd. Well receives water from entire thickness of aquifere. Transmissivity is constantf. Pumping is constant 5)Transient flow conditions (Nonequilibrium)a. The cone of depression continues to flow over time b. To reach steady state conditions, one must know storativity (S), transmissivity (T),boundary conditions (BC), and the pumping rate (Q)i. Storativity1. High – more water in defined area2. Low – less water in defined areaii. Transmissivity1. High – water flows more easily (can have a low gradient)2. Low – water does not flow easily (requires a steeper gradient)3. Pumping rate and transmissivity coincide4. If you have low T, you must have higher Q6)Pumping ratea. Negative drawdown – pumping outb. Positive drawdown – pumping in 7)Boundariesa. If there is a boundary near the well, the drawdown will be influenced by