Hydrology of the black swamp wetlands on the Cache River, Arkansas

Abstract

The hydrologic characteristics of the Cache River wetlands between Patterson and Cotton Plant, Arkansas, were investigated. The Cache River is an underfit stream with wetlands predominantly located in abandoned channels and backswamps. Much of the Cache River upstream of the study area has undergone extensive channelization to allow agricultural development in the basin. Hydrologic measurements included streamflow gages at the upstream and downstream limits of the study area. water-level recorders inside the study area, a nest of deep and shallow ground-water wells that monitored variations in the underlying aquifer, a meteorological recording station that collected precipitation, air temperature, and solar radiation data inside the study area, and regional precipitation data. Analysis of the wetland’s water budget showed that the system is dominated by river discharges and that the magnitudes of other water-budget components are less than the error associated with well-maintained streamflow gages (5–10%). The system is characterized by floods occurring from late fall to late winter and again in mid-to-late spring. Peak flood discharges are approximately 185 m3/s for a 2-year event and 270 m3/s for a 5-year event. Peak discharges between the upstream and downstream gages are reduced by 10–20% with greater attenuation occurring when the system is initially drier. Peak discharge at the downstream gage lags the peak at the upstream gage by 4–8 days depending on antecedent conditions. The majority of overbank flooding is produced by backwater from several constrictions in the downstream reach of the study area, rather than from the forward movement of the flood wave. Flodpeak attenuation between the upstream and downstream gages is due mainly to floodplain storage, with flow resistance contributing minimally. Finally, the relationship between the hydroperiods at different water-surface elevation gages was examined to determine if a long-term record could be used to estimate long-term hydroperiods at interior gage locations (or perhaps at interior computer model locations) with shorter-term information.