Buffalo Bayou Hurricane Hike
Stop 1 // WATER // Hydrologic Archive
Middle of Shepherd Pedestrian Bridge
Looking east (downstream), the base of the tall AIG building is the Hurricane Harvey high water mark (Fig. 1.1). Figure 1.2 is the view west (upstream), with high water marks for major flow events. Though Harvey had a dramatic impact on Houston it is not an unprecedented event. The 1929 and 1935 flow events as measured here were significantly higher than that of Harvey. The 1879 event projected from Allen’s Landing was also probably higher than Harvey’s (higher than 1929 but lower than 1935). From the perspective of a long lifetime, the water level associated with Harvey is not unusual. In the context of increasing global weather extremes we should expect Harvey-like high flow events to become even more the norm.
Figure 1.1. View looking east (downstream) one year after Harvey. The water rose to the base of the AIG building on the right. The red line marks the approximate limit of flooding from Hurricane Harvey. The sand to the lower left was highly modified by Harvey.
Figure 1.2. View looking west (upstream) under the Shepherd St. bridge. The United States Geologic Survey Shepherd Street Bridge Buffalo Bayou river gauge can be seen under the bridge. The bold solid red line marks the Harvey flood level of 12.77 m (41.9 ft; USGS, 2017a). The thinner red lines are 3 higher water levels: 1935 – 14.93 m (49 ft), 1879 – 13.7 m (45 feet; estimated), and 1929 – 13.70 m (43.5 ft) and 2 recent lesser storms, Imelda, 2019 - 9.8 m (32 feet) and Tax Day storm, 2016 - 9.4 m (31 feet).
The hydrologic archive recorded by the stream gauge is shown in the water level vs time plot (Fig. 1.3). The energy level of the flow is directly related to the water level. The evolution of the water level has been divided into several phases:
Pre-Harvey day -3 and earlier
Flood phase day -2 to 0
Peak water level day 0 (August 28, 2017)
Early adjustment day 0 to 2
Middle adjustment day 2 to 18
Late adjustment day 34 to 93
Recovery day 94 to 110+
Figure 1.3. Hurricane Harvey Buffalo Bayou water level. The chart plots Buffalo Bayou water level at the Shepherd St. bridge (solid dark blue line in feet elevation scale, on left; USGS, 2017a) vs time (110 days after Harvey). The red line marks the peak water level of almost 12.8 m (42 ft). At the top of the chart are the flow phases: pre-Harvey (yellow), flood (red), adjustment (green), and recovery (blue). The colors correspond to those used in the map (Fig. 0.1) and sand peel interpretations (Plates 1-12).
In the pre-Harvey phase, the flow and sediment load are in near balance and relatively small amounts of sediment are transported. During the flood phase the water level is rapidly rising and sharply increasing in flow energy, scouring sediment out of the bayou channel until the peak water level is reached. As the water level and energy of the flow decline the flow can no longer carry the full sediment load and the adjustment phase begins. During the early adjustment phase the energy level drops dramatically, leading to significant deposition of sediment. During the middle adjustment phase the energy level is much lower and the character of the sediments dropping out of suspension changes. In the late adjustment phase the bayou is returning to its normal channel and is redistributing sediments deposited during the early and middle adjustment phases. During the recovery phase, water and flow energy return to pre-Harvey levels and man is the main mover of sediment.
During Hurricane Harvey the water level rapidly rose, then dropped in 2 stages until the bayou returned to its channel in roughly 30 days. Approximately 100 days after Harvey the flow was back to normal.
The water level data was sourced from the USGS website which displays gauge height data from a stream gauge located under the road bridge at Shepherd and Allen Parkway.