Scientific Investigations Report 2009-5130
AbstractAn ecological field and modeling study was conducted to examine the flood relations of backswamp forests and park trails of the flood plain portion of Congaree National Park, S.C. Continuous water level gages were distributed across the length and width of the flood plain portion—referred to as “Congaree Swamp”—to facilitate understanding of the lag and peak flood coupling with stage of the Congaree River. A severe and prolonged drought at study start in 2001 extended into late 2002 before backswamp zones circulated floodwaters. Water levels were monitored at 10 gaging stations over a 4-year period from 2002 to 2006. Historical water level stage and discharge data from the Congaree River were digitized from published sources and U.S. Geological Survey (USGS) archives to obtain long-term daily averages for an upstream gage at Columbia, S.C., dating back to 1892. Elevation of ground surface was surveyed for all park trails, water level gages, and additional circuits of roads and boundaries. Rectified elevation data were interpolated into a digital elevation model of the park trail system. Regression models were applied to establish time lags and stage relations between gages at Columbia, S.C., and gages in the upper, middle, and lower reaches of the river and backswamp within the park. Flood relations among backswamp gages exhibited different retention and recession behavior between flood plain reaches with greater hydroperiod in the lower reach than those in the upper and middle reaches of the Congaree Swamp. A flood plain inundation model was developed from gage relations to predict critical river stages and potential inundation of hiking trails on a real-time basis and to forecast the 24-hour flood In addition, tree-ring analysis was used to evaluate the
effects of flood events and flooding history on forest resources
at Congaree National Park. Tree cores were collected from
populations of loblolly pine (Pinus taeda), baldcypress
(Taxodium distichum), water tupelo (Nyssa aquatica), green
ash (Fraxinus pennslyvanica), laurel oak (Quercus laurifolia),
swamp chestnut oak (Quercus michauxii), and sycamore
(Plantanus occidentalis) within Congaree Swamp in highand
low-elevation sites characteristic of shorter and longer
flood duration and related to upriver flood controls and dam
operation. Ring counts and dating indicated that all loblolly
pine trees and nearly all baldcypress collections in this study
are postsettlement recruits and old-growth cohorts, dating
from 100 to 300 years in age. Most hardwood species and
trees cored for age analysis were less than 100 years old,
demonstrating robust growth and high site quality. Growth
chronologies of loblolly pine and baldcypress exhibited
positive and negative inflections over the last century that
corresponded with climate history and residual effects of
Hurricane Hugo in 1989. Stemwood production on average
was less for trees and species on sites with longer flood
retention and hydroperiod affected more by groundwater
seepage and site elevation than river floods. Water level data
provided evidence that stream regulation and operations
of the Saluda Dam (post-1934) have actually increased
the average daily water stage in the Congaree River. There
was no difference in tree growth response by species or
hydrogeomorphic setting to predam and postdam flood
conditions and river stage. Climate-growth analysis showed
that long-term growth variation is controlled more by spring/
summer temperatures in loblolly pine and by spring/summer
precipitation in baldcypress than flooding history. |
First posted July 24, 2009 Part or all of this report is presented in Portable Document Format (PDF); the latest version of Adobe Reader or similar software is required to view it. Download the latest version of Adobe Reader, free of charge. |
Doyle, T.W., 2009, Modeling flood plain hydrology and forest productivity of Congaree Swamp, South Carolina: U.S.
Geological Survey Scientific Investigations Report 2009–5130, 46 p.
Abstract
Introduction
Coastal Plain Forest Ecosystems
Productivity Studies of Coastal Plain Forests
Environmental Setting
Congaree Swamp
Saluda Dam
Climate
Temperature
Precipitation
Palmer Drought Severity Index
Hurricanes
Purpose and Scope
Methods
Water Level Monitoring
Tree Core Collections and Measurement
Growth Calculations and Analysis
Results
Hydrological and Trail Elevation Surveys
Flood Plain Inundation Model
Tree-Ring Analysis
Forest Age and History
Loblolly Pine Chronology Development and Productivity
Loblolly Pine Climate-Growth Relations
Baldcypress Chronology Development and Productivity
Baldcypress Climate-Growth Relations
Saluda Dam Effects on River Stage and Tree Growth
Summary
Acknowledgments
References