Head Dependent Boundaries in MODFLOW88 Q = C h River Package Drain Package General Head Boundary (GHB) Package ET Package

River Package Q = C (hR – hijk) where C =KvLw/m

Drain Package

Drain Package Q = C (hijk-d) Q = 0 if hijk<d where d = head in the drain. Q = 0 if hijk<d

General Head Boundary Package Boundary cell hB L h Q= C (hB-h) C = K A /L

Lake Model hB L GHB Q = C (hB - h) C = Conductance = K A/L K is the hydraulic conductivity of the aquifer between the model and the lake; A is the area of the boundary cell, perpendicular to flow.

Evapotranspiration (EVT) Package …to be discussed later, when we do the Final Project

New MODFLOW Packages to simulate dynamic interchange between groundwater and surface water • Stream Package (Prudic, 1989) • MODBRANCH (Swain, 1993) • Lake Package (Cheng and Anderson, GW,1993) (Council, 1998) (Merritt and Konikow, 2000) • Wetland Module (Restrepo et al., GW,1998)

Lake (LAK) Package Change in Storage = Outflow - Inflow Change in lake level = Change in Storage/Area

Transient Simulations require: Initial Conditions Storage Coefficient Time step

Types of Initial Conditions Static steady state Dynamic steady state Dynamic cyclic conditions (Time distant conditions)