Modifying the Bank Erosion Hazard Index (BEHI) Protocol for Rapid Assessment of Streambank Erosion in Northeastern Ohio

Cleveland Metro Parks proudly presents modifying the bank erosion hazard index protocol for rapid assessment of stream bank erosion in northeastern Ohio. Section one, introduction stream bank erosion is a natural process, however, in excess erosion can be a cause of major non-point source pollution from suspended sediment Acclaimed hydrologist, Dr.David Roskin of wildland hydrology in Colorado developed the BHI or bank erosion hazard index, which utilizes a variety of indicators to rank the severity and susceptibility of stream bank erosion. The original behi method, while useful, can be time consuming, difficult for non-professionals and is confined to specific alluvial environments in southern Colorado.

Cleveland Metro Parks a 23, 000 acre park system across northeast Ohio attempts to determine the volume source and rate of stream bank erosion to assist in land management and restoration efforts. Modifications to roskins protocol adapt the beehive procedures to the geomorphic settings of northeast Ohio waterways. Further alterations were made to enable citizen science volunteers to complete the behi protocol.

With introductory training, we only assess the banks that are for more information on the original behi procedure. Refer to the book Watershed Assessment of River Stability and Sediment Supply. Section two changes to raskin's behi modifications to the behi protocol begin with a pre-screening questionnaire to identify and eliminate stream banks likely to rank very low or low.Okay.

This directs focus to the higher erosion areas and decreases the amount of time and resources required to perform a behi assessment on an entire stream. The questionnaire considers the geologic differences between northeastern Ohio and southern Colorado by addressing non alluvial boundary conditions such as Ohio's erodible Shale, which would not have been assessed as an erodible material based on the original beehive protocol. Elimination of the study bank height ratio metric, including the bank full stage, which can be very difficult to determine, allowed for a faster stream bank assessment and for non-professionals to complete the evaluation accurately to eliminate additional calculations in the field.

All other metrics were modified to be expressed as percentages except for bank angle stratification and bank material adjustments. Scores were altered to account for the modifications. Section three, modified BHI pre-screening questionnaire similar to roskins original protocol are modified BHI starts with identifying a uniform section of bank.

This section could be differentiated by a change in slope, a break in vegetation or a different bank material. There is not a minimum or maximum length for the bank. Extremely long sections can be separated into smaller segments.

However, this is not necessary. In order to complete the modified behi protocol, a stream section must exhibit two or more of the following pre-screening criteria. If the bank does not exhibit two or more, do not proceed with the behi protocol as little or no erosion is occurring.

Does the uniform section of bank exhibit less than or equal to 50%protection at the toe? The toe is located at the base of the bank where it meets the water. On average, the bottom six to eight inches of the bank protections include embedded boulders, embedded large woody debris and rooted vegetation.

Bedrock counts as toe protection. However, if you're able to easily break the pieces of the bedrock, this does not count as tote protection. Does 50%or more of the bank exhibit an undercut of half a foot or more?

Undercut banks have a higher risk of bank failure due to gravitational forces and sheer stresses does 50%or more of the bank exhibit stratification. Stratification is a clearly defined horizontal bra in geology that may cause zones of preferential erosion within the banks that have more than one strata. Does more than half of the section have a bank height of 10 feet or more with 50%or more soil exposure?

Oftentimes this is indicative of an inized channel with a loss of the riparian buffer. Does 50%or more of the bank exhibit roots lacking bank material in excess of hanging roots in the stream can signify active erosion? Is 50%or more of the bank void of rooted vegetation?

Rooted vegetation helps protect the bank material from erosive forces based on the results from the pre-screening questionnaire if a BHI evaluation is needed. Note the questions which had a yes on the data sheet. Section four, modified BHI data sheet record.

The date personnel involved weather and general area information. Bank number is an arbitrarily assigned reference number given to the bank's assessed standing close to the bank. Take GPS coordinates at the upstream and downstream points.

Capture photographs of both locations showing the bank and channel features. Bank refers to the side of the stream. You are assessing the left and right are determined when facing downstream.

Bank height is a measurement from the toe to the top of the bank. The top can be determined by the first definable break and slope. Bank length is a measurement between the most upstream and most downstream points under evaluation.

Note the distance to the nearest infrastructure and the type circle. Any qualitative indicators that are present record the composition of the bank materials. Stream banks can be a mix of materials.

For example, a bank may have shale at the toe and silty sand with trace gravel above silty sand indicates more sand than silt and trace. Gravel indicates a small amount of gravel when classifying material types use the following criteria. Bank material adjustments can be made to account for erosive differences.

Up to 10 points can be added or subtracted based on the erod ability of the materials. A mixture of materials such as sand with some gravel or silty sand with trace gravel is more often found in stream systems, so an average adjustment would be more appropriate. This is not a mandatory adjustment.

Riparian root depth is a ratio of the average root depth of the plants to the study bank height expressed as a percentage. Visually estimate the root depth vertically from the top of the bank to the toe. For example, if roots are growing in the top portion of the bank, the root depth would be 35%Do not consider hanging roots that are void of bank material.

Estimate a percentage based on the entire bank. Then use the BHI score chart to record the score on the data sheet. Root density is a visual assessment of the amount of bank composed of root material expressed as a percentage.

Do not consider hanging roots that are void of bank material. Small fibrous roots can be very dense and provide greater soil retention compared to large tap root systems. Estimate a percentage based on the entire bank.

Then reference the BHI score chart and record The data. Bank angle is the angle from the toe to the top of the bank. Steeper bank angles are estimated to have a higher risk of mass failure due to gravitational forces.

Ensure stresses take an average of the bank angle along the entire section under evaluation. For example, if the section is mostly 90 degrees with a small section that has a 110 degree undercut, the recorded degree would be approximately 100. Estimate an angle based on the entire bank utilizing the score chart to determine the recorded value.

Surface protection is the amount of stream bank covered and protected by woody debris rooted vegetation embedded and bedrock. This is measured as the percentage of the stream bank not exposed to erosive forces. Estimate a percentage based on the entire bank.

Then use the score chart to log the value stratification. Adjustments can be made if increased erosion is occurring due to the stratified layers. Up to five points can be added for a single layer or up to 10 points can be added for multiple layers of stratification.

Only adjust for stratification if at least one layer of material is erodible, such as sander gravel. Consider where the stratified layers are in relation to the water. Stratified layers that are significantly above the water may not have an erosive effect.

Stratified layers near the toe may have an extremely erosive effect. This is not a mandatory adjustment. Add all the scores together to determine the overall B.High rating.

Very low, low, moderate, high, very high or extreme record. The total score and the rating in the notes record stream and bank specific such as the stream bank is on the outside of a meander bend. Large woody debris jams, infrastructure damage, strong petroleum motor or water sheen.

Section five representative results. The stream banks that passed the pre-screening questionnaire and were not assessed with our modified BHI ranked low or very low when assessed with Rogan's original protocol. 16 out of the 18 stream banks assessed with both protocols had the same final rating.

This particular bank scored a 23.0 using the modified protocol, which is 0.5 below the cutoff between a moderate and high BHI rating. Using the original protocol, the bank scored 31.25 a high BHI rating. However, the score was within 1.25 of the cutoff between moderate and high.

The slight difference in the final rating can be attributed to the cutoff margins within the scoring system. The other bank with the differing BHI rating was a weathered shale wall that was unable to be assessed with the original BHI protocol as bedrock automatically receives a very low BHI score. However, this stream bank failed the prescreening questionnaire due to the lack of toe protection.

A bank hike greater than 10 feet with more than 50%soil exposure and more than 50%of the bank was void of rooted vegetation. Therefore, an assessment using the modified BHI protocol was necessary. The final rating using the modified be high protocol was extreme, which is supported by the steep bank angle, extremely erodible material, lack of a riparian root system, and small amount of surface protection present.

When assessing the overall health of the stream, it is recommended that the final numerical scores are considered to best encapsulate the range of scores. Each rating represents. Section six.

Conclusion, the modified beehive protocol is effective for ranking and prioritizing stream bank erosion to assist in formulating stream management strategies. However, due to the removal of the bank full height metric, our model cannot be used to predict annual stream bank erosion rates. A bank assessment for non-point consequence of sediment model should be completed if annual stream bank erosion rates are desired through modifications.

We have effectively repurposed Dr.Rogan's original bank erosion hazard index protocol to yield valuable information within the geomorphic landscape of Northeast Ohio.