Harmonic Analysis Can Assess Hydrologic Cumulative Impacts
Abstract
This note describes an aid for assessing cumulative impacts on wetlands. Harmonic analysis techniques are employed to reveal time frames when disruption to basic flow patterns may have occurred. Water-level patterns largely determine the nature of wetlands. Therefore, studies of historic water trends associated with wetlands should explain causes and effects operating on wetlands and the resulting landscape/biotic composition. Keys to characterizing historic water-level trends are called hydrologic indices. Hydrologic indices may be categorized as either simple or complex. Simple indices are easy to compute and include parameters such as mean, median, and range of flows. However, these indices often fail to adequately describe periodicity, seasonal behavior, or evolution of stream character resulting from land use changes and channelization. Despite obvious limitations, such simple indices can reveal important features of streamflow and how they compare with those of other streams in the same basin. These simple indices also can give clues regarding the timing of historic, momentous events, such as the abrupt decrease of the monthly maximum flow in the Little Red River record (1961) shown in Figure 1 with records of other selected streams in the White River Basin (Arkansas/Missouri). The effects of more subtle but perhaps no less profound impacts may be better detected and quantified using indices that are somewhat more complicated to derive, but which may yield more insight into cumulative impact analysis. One such index, harmonic analysis, is presented here. Harmonic analysis can show not only periodicity, but also change in a stream's character over time. The flow record of the Cache River at Patterson, Arkansas, is examined using harmonic analysis. Streamflow and ground water records in conjunction with land use histories and remote sensing can contribute to cumulative impact analysis.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 01, 1994
- Accession Number
- ADA434513
Entities
People
- Katherine S. Long