OPTIMIZATION MODEL FOR GROUNDWATER DEVELOPMENT IN COASTAL AREAS - Advances in Geosciences - page 162

Table 1. Types of common groundwater development problems.

Apriori determined Decision variables Optimization

variables
Stage 1: Optimal arrangement of pumping wells
CATIA Location Freshwater pumping rate Minimize adverse

impacts

CATIB Pumping rate Location Maximize pumping rate

CAT2A — Location and freshwater

pumping rate

Maximize pumping rate
while minimizing
adverse impacts

Stage 2: Control of saltwater wedge
CAT2B

— Locations and freshwater

pumping rate or injecting
rate

Maximize pumping rate
while minimizing
adverse impacts

CAT4 — Locations and freshwater

pumping rate or
saltwater pumping rate

Maximize pumping rate
while minimizing
adverse impacts

there are existing wells that may be affected by the new pumping wells
or impacts on the groundwater environment are to be considered. When
the desired pumping rates are predetermined, the problem reduces to find-
ing the optimal locations. This type of problem is referred as the second
type. Multiple optimal solutions may arise if impacts on the groundwa-
ter environment are not considered. The third type involves problems of
finding both the optimal pumping rates and the optimal locations. When
more groundwater pumping is required than the optimal pumping rate,
a saltwater-wedge control method can be used. Freshwater injection and
saltwater pumping can achieve the goal.

3. Example Application

The proposed optimization model is applied to an example problem. The
modeling domain is an unconfined aquifer, 40 m thick, and 1 . 5km × 1 . 5km

wide (Fig. 2).
The aquifer is assumed to be heterogeneous with four distinct permeabil-
ity zones of four orders of magnitude differences. There is a coastal line on
the right side. Freshwater enters the domain at the rate of 0.52 m 3 /day/m 2
through the left side. The densities of freshwater and seawater are 1,000
and 1,025 kg/m 3 , respectively.