Environmental Engineering Reference
In-Depth Information
9
Linking estimation methods to conceptual
models of groundwater recharge
final thoughts related to future developments
in estimating groundwater recharge.
9.1 Introduction
The selection of appropriate methods for esti-
mating groundwater recharge should be tied
to a conceptual model of recharge processes;
assumptions inherent in any method must
be consistent with that conceptual model.
The emphasis of
Chapters 2
through
8
was
on estimation methods. Various categories of
methods were described and systematically
analyzed with particular attention to under-
lying assumptions. The objectives of this final
chapter are to illustrate how methods for esti-
mating recharge are tied to conceptual mod-
els and to provide some broad guidelines for
selecting methods.
Section 9.2
provides a reexamination of the
conceptual model development discussed in
Chapter 1
in light of the information provided
in the intervening chapters. A comparison of
the various families of methods is provided in
Section 9.3
; tables summarize recharge proc-
esses, space and time scales of applicability, and
the relative expense and complexity of methods.
Section 9.4
contains discussions of conceptual
models of recharge processes that have been
developed and used within different ground-
water regions of the United States. Also included
in
Section 9.4
are discussions of methods that
have been applied in support of those concep-
tual models and a necessarily brief sampling
of recharge studies that have been conducted
within each region. The chapter concludes with
9.2 Considerations in selecting
methods for estimating recharge
The first consideration in selecting methods
for estimating recharge is the goal of the study
(e.g. to assess water resources of a basin, to
provide model input, to evaluate potential for
groundwater contamination). Forming an ini-
tial conceptual model of the hydrologic system
is the next step. The conceptual model identi-
fies the prominent recharge mechanisms, pro-
vides initial estimates of recharge rates, and
serves as a guide for the selection of methods
and of locations and times for data collection.
Recharge processes are largely controlled by
climate, geology and soils, topography, hydrol-
ogy, and vegetation and land use; these factors
need to be considered in formulating the con-
ceptual model. Analysis of existing data and the
results of recharge studies in similar areas can
help to shape the initial conceptual model. The
conceptual model usually evolves over time as
data are collected and analyzed; new informa-
tion and interpretations may support revision
of the conceptual model or suggest the applica-
tion of alternative approaches. It is important
to identify recharge mechanisms because some
methods are specifically designed to estimate
focused recharge, whereas others are designed
for estimating diffuse recharge exclusively.
