Houston Ball Field Erosion Study

The Upper Chartiers Creek Watershed Association (UCCWA) has set the goal of addressing a severely eroding bank along Chartiers Creek adjacent to a public baseball field in Houston, PA (Washington County). The reach of interest is approximately 1,035 feet of the left descending bank owned by Houston Borough, which has expressed support for the project (Figure 1). To gather evidence of erosion to strengthen funding requests, UCCWA applied for assistance through the  3 Rivers QUEST GAPS program . Through this program, the West Virginia Water Research Institute (WVWRI) conducted a small-scale erosion study with the assistance of UCCWA volunteers. WVWRI installed erosion pins, conducted initial measurements, trained volunteers to collect monthly measurements, and compiled results.

Erosion pin methodology was selected due to its ability to monitor relatively small changes through a short-term study, as well as its low cost. Erosion pins are lengths of metal inserted into the streambank with a known length of pin left exposed. When soil is eroded, re-measurement reveals a greater exposed length. Through subsequent measurements, one can estimate the rate of bank retreat based on the difference between the new exposed pin length and the original exposed pin length (Staley et al., 2006). It should be noted that erosion pins do not determine the cause of erosion. The purpose of this study is to provide quantitative measurements of erosion. The methodology for pin spacing, installation, and measurement was adapted from methods described in Staley et al., 2006 and Rando et al., 2017.

Pins were installed within 3 subsections representing the bank conditions within the study area (Figure 2).

The exposed length of each pin was measured monthly by UCCWA volunteers beginning one month after installation. During each trip, the volunteers recorded weather conditions, pin measurements, and notes regarding any mass failures or disturbances to pins. Care was taken by volunteers to minimize soil disturbance and to record even very small differences (2 mm).

Volunteers accessed the stream in the area shown in Figure 5, then walked to each pin transect, where they measured each pin’s exposed length. Measurements were taken utilizing a high-precision 15-cm digital caliper (Fisher Scientific), from the pin end to the bank surface at the vertical centerline along the downstream side of the pin (parallel with the stream) until contact was made with the soil surface and slight sediment movement was observed without compaction. After measurements were recorded, pins were reset to their original length indicated in the field data sheet. However, pins with changes of less than 10 mm were not reset to minimize disturbance and error. Those pins were reset in subsequent months once the total change was greater than 10 mm, as compared to the original exposed length. Pins buried due to deposition were noted on the field sheet continuously until they became exposed again. In the event of a mass failure (a section of the bank sliding into the stream) or other cases of pin displacement, photos and notes were taken, and the pin was reset in a location as close to the original location as possible.

UCCWA collected pin measurements monthly from May through October 2023, and repeated measurement again in April of 2024. The April 2024 sample offers results one year after the pin installation. This took place after a winter of high flows, followed by significant flooding in early spring. During this visit, it was observed that 5 pins had been washed out since the measurements taken in October of 2023. The lost pins were not used in calculating the overall study average since their final measurements were unknown.

Results from the monthly measurements are summarized in Figure 6, where a positive change (brown) indicates erosion, and a negative change (green) indicates deposition. The most widespread erosion occurred in the spring (April – May 2023) and over the winter (October 2023 – April 2024). The average net erosion among the pins was 7.35 mm over the first 6 months and 33.96 mm over the full length of the study. However, one pin showed as much as 101.29 mm (4 inches) of erosion over the year. Taking the net change in the pin lengths over the year concludes that 10 pins experienced net erosion, 3 pins experienced net deposition, and 5 pins were washed out entirely (Figure 7).

During the year of study, erosion was measured at all three subsections. This data backs up visual evidence of erosion, such as exposed roots and crumbling banks, seen throughout the length of the park. Importantly, five of the six pins located in subsection C were washed out during the winter or early spring, indicating that this area experiences the most erosion and should be prioritized for streambank stabilization. Visual evidence of the erosion is shown when comparing the photos from April 2023 and May 2024 (Figure 8).

Significant flooding occurred at the site in early April 2024 (Figure 9). Imaging from the Pennsylvania Flood Risk Map (Figure 10) shows that the Houston Ball Field is a regulatory floodway, which is defined by FEMA as the channel of a river or other watercourse and the adjacent land area that is reserved from encroachment in order to discharge the base flood without cumulatively increasing the water-surface elevation by more than a designated height.

Accordingly, FEMA states that communities must regulate development in these floodways to ensure that there are no increases in upstream flood elevations. It is predicted that the severity and frequency of flooding events will be amplified due to climate change (Easterling et al., 2017). Therefore, it is crucial to take proactive steps now to stabilize the already eroding stream bank at the Houston Ball Field.

For more details about the study, please view our  technical report .