Types of Boundary Conditions 1. Specified head (including constant head) h = f (x,y,z,t) 2. Specified flux (including no flow) h/l = -q l /K l 3. Head-dependent conditions q = -K b (h b – h)/b Implementation in MODFLOW
Types of Boundary Conditions
1. Specified head (including constant head) h = f (x,y,z,t)
2. Specified flux (including no flow)
h/l = -ql/Kl
3. Head-dependent conditions
q = -Kb (hb – h)/b
Implementation in MODFLOW
Definitions
Riverbed Conductance = (Kv/m) wL
Leakance = Kv/m
Resistance = m/Kv
Kv = vertical hydraulic conductivity of riverbed sediments
m = thickness of riverbed sedimentsw = width of the riverL = length of the river within the cell
River with sandy bottom = 1 day
Small stream with silty bottom = 1- 10 days
Stream/lake in till = 100 days
Resistance
Head Dependent Boundariesin MODFLOW88/96
• River Package• Drain Package• General Head Boundary (GHB) Package• ET Package
Q = C h
hB
L
C = Conductance = K A/LK is the hydraulic conductivity of the aquifer between the model and the lake;A is the area of the boundary cell, perpendicular to flow.
GHB
Q = C (hB - h)
• Streamflow Routing Package (Prudic 2004)
New MODFLOW Package available in MODFLOW2000.
• Streamflow Package (Prudic 1989)- see p. 127 A&W Q
Allows for dynamic interchange ofgroundwater and streamflow; solvesfor stream stage.
Manning’s Equation:
d = (Q n / C w S1/2)3/5
n is Manning’s Roughness coefficient
• Lake Package – Available in MODFLOW2000
(Cheng and Anderson, GW,1993) (Council, 1998) (Merritt and Konikow, 2000)
• MODBRANCH (Swain, 1993)
• Wetland Module (Restrepo et al., GW,1998)
Other packages:
Solves for lake levels
Lake (LAK) Package
Change in lake level = Change in Storage/Area
Change in Storage = Outflow - Inflow