WRIR 78-76

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### Tibbals, C.H, 1978, Effects of Paved Surfaces on Recharge to the Floridan Aquifer in
East-Central Florida--A Conceptual Model, 43 p.

Abstract

The proportionate amount of surface area that can be paved in Floridan aquifer recharge
areas in east-central Florida without reducing the net recharge to the Floridan aquifer
is a function of many variables that include rainfall, depth to water table, depth to
potentiometric surface of the Floridan, evaporation from paved areas, evapotranspiration
from unpaved areas, runoff, pattern of paving, and leakance coefficient of the confining beds.
Equations that incorporate those variables, except pattern of paving, are developed and
coupled to produce a conceptual model that estimates relative amounts of water available
for recharge and percentage of unpaved area below which Floridan aquifer recharge rates must
increase. An assumption inherent in the use of the model is that the excess water that runs
off from the paved areas is placed in the nonartesian aquifer in the unpaved area so that the
water table rises and thus increases the hydraulic head difference between the nonartesian and
Floridan aquifers. Thus, water is driven across the confining beds and into the Floridan at
a rate that is sufficiently increased so as to make up for the reduced area due to paving
under which recharge actually occurs. Many assumptions and stipulations are made to simplify
the model. The model is not intended to be used as a basis for engineering design. Rather,
its purpose is to show approximate mathematical interrelations of rainfall, runoff,
evapotranspiration, percentage of paving, and Floridan aquifer recharge, and to make
quantitative estimates of amounts of water available for Floridan aquifer recharge before
and after paving. The allowable percentage of paving calculated in 4 examples ranges from
86.8 percent to 3.6 percent.

### TABLE OF CONTENTS

Abstract

Abstract

Introduction

Notation and units

Hydrologic cycle Development of conceptual model

Example 1
Case 1, no allowable increase in runoff after paving
Case 2, unrestricted runoff after paving
Examples 2, 3 and 4

Correction for buildup of potentiometric surface of Floridan aquifer
Computer model used to correct buildup of potentiometric surface of Floridan aquifer

Summary

Selected referencess

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