Roadbank Inventory

Methodology

A visual survey was performed on all roads in the watershed to obtain the information needed to rank the erosion potential of each road segment. The information gathered allows for a relative roadbank severity classification. All roads can be ranked according to their erosion potential.

Erosion in road ditches is categorized as moderate, severe, or very severe (1225 sites in the watershed). Those roads not listed in the three categories during this survey fall into the none category. The categorization reflected both subjective and objective standards. Ditch width and depth measurements were collected at representative problematic roadbank sites throughout the watershed. These measurements were used to calculate sediment loading from road ditches for the categories of moderate, severe and very severe. Calculations were taken from the USDA Engineering Field Manual, Chapter 3 Hydraulics, Exhibit 3-3 pp. 3-95. The parabolic shape was used since it most closely represents the shape of road banks.

Site locations where digitzed into a geographical information system. The collected data was then joined to the site locations for the purposed of mapping and analysis.

Very severe: implies cut, bare and collapsing banks, exposed roots, and "blow-out" holes in ditch bottoms and gully erosion with soil losses ranging from 97 to 188 tons per bankside mile. Soil loss is calculated for each representative site using a subjective average loss of 2 inches (.166 ft) over a parabolic wetted perimeter divided by three. An average figure of 144 tons of soil erosion per bank side mile is calculated and applied to determine the tons of soil loss over the miles of roads having very severe erosion. Usually "very severe" conditions were found to be on slopes greater than 8%.

Severe: bare banks, some collapsing of banks, some exposed roots, bare ditch bottoms and deposition of larger stones with soil losses ranging from 25 to 107 tons per bankside mile. Soil loss is calculated for each representative site using an subjective average loss of 1 inch (.083 ft) over a parabolic wetted perimeter divided by three. An average figure of 60 tons of soil erosion per bankside mile was calculated and applied to determine the tons of soil loss over the miles of roads having severe erosion. Usually, "severe" conditions occur in road ditches with slopes ranging from 5% to 8%.

Moderate: channel having the presence of vegetation for considerable length with evidence of some cutting and deposition. The range of soil loss for such conditions ranges from 10 to 55 tons per bankside mile. Soil loss is calculated for each representative site using an average loss of inch (.042 ft) over a parabolic wetted perimeter divided by three. An average figure of 23 tons of soil erosion per bankside mile is calculated and applied to determine the tons of soil loss over the miles of roads having moderate erosion. This condition usually occurs on road ditches having slopes less than 5%.

For calculating sediment loading from road ditches that did not fall into the very severe, severe, or moderate categories, a base figure of 8.2 tons per mile is used. (equivalent to the scouring of inch of soil).

The following calculation shows the tons of soil loss per bankside mile per year for a given bank classified "very severe":

Soil Loss = (wp/3)(0.166 ft)(5280 ft)(.044 T/ft3)

Wp ( wetted perimeter) = (T + (8d2 / 3T),

where, T = ditch width and d = ditch depth.

(0.166 ft= 2 inches) (5280 ft = 1 mile)

(.044 T/ft3 = soil weight)

Using the soils handbook from USDA, NRCS, the weight for clay, silty, sands and sandy loams ranges from 65 to 110 pounds per cubic foot. An average weight of 87.5 pounds is converted to Tons per cubic foot. The method used to calculate erosion stemming from road ditch sources is intended as an indicator of relative severity. Its scope is limited, however, in that it does not account for soil losses from the road sub-surface (or surface on gravel or dirt roads) nor from exposed banks adjacent to the road ditches. Soil losses from the latter, in particular, can be very severe depending upon the steepness of the slopes.

Data collected in the field include the following: eroded distance, slope, depth, width, exposed roots, collapsing banks, washed out gravel, new dug/bare soil, vegetative cover, location relative to land use, and erosion class.

Analysis

The northwest portion of the watershed has relatively few problems with roadbank erosion with a few exceptions in Bloomer/Mack Creeks Area and the Sheldrake Creek subwatershed. The northeastern portion of the watershed has more significant roadbank erosion. Generally, the closer the road ditches are to the lake the more erosion is occurring mainly due to the steep gradients from the upland portions of the watershed down to the lake. This is demonstrated in the numerous road ditches classified as "very severe" in the King Ferry area. The same is true further south in the Lansing area. The southwestern portion of the watershed has some very severe erosion occurring along the road ditches in the Spring Brook, Taughannock Creek, Enfield Creek, and Willow Creek area. The large subwatersheds in the southern portion of the watershed with the exception of the Virgil, Cascadilla, and Buttermilk Creek subwatersheds have numerous road ditches classified as "very severe". Map 3.4.1 shows the moderate, severe and very severe sites. The following is a brief description of roadbank erosion in the subwatersheds of the Cayuga Lake Watershed:

Barnum Creek - There are eleven sites sampled in this area, and all of them are classified as moderate.

Big Hollow Area - There are 12 sites in this subwatershed. Eight of the twelve are classified as moderate; 2 are

classified as severe; and two are classified as very severe. The four road ditches not classified as moderate may be of some concern because they are all near the lake’s shore; therefore sediment has little distance to travel before it flows into the lake.

Big Salmon Creek - The road ditches in this subwatershed are in fairly good shape. There are only two sites in the severe category.

Bloomer/Mack Creeks Area - This direct drainage area has five road ditches considered to be in the severe category. This is a significant concern given they're proximity to the lake.

Boardman Creek - There are only seven areas documented for their eroded condition. Only one of them is considered to be severe.

Bolter Creek - The overall roadbank condition of this watershed is fairly good. Only seven sites were documented for their erosion, one of which is considered to be severe.

Buttermilk Creek Area - Road ditches in this subwatershed are slightly eroded. There are seven sites classified as severely eroded.

Canoga Creek Area - There are a few areas designated as moderately eroded..

Cascadilla Creek - There are a number of roadbank sites documented, but they are mostly in the moderate category. Four sites are classified as severe.

Cayuga Inlet - This subwatershed appears to have serious roadbank erosion. There are a number of road ditches documented as having moderate or severe erosion problems. Eight sites are considered very severe.

Cayuga View Area - Three roadbank sites are classified in this small subwatershed. Two are severe and one is moderately eroded. All three of these sites are located near the lakeshore.

Cayuga Village Area - This small subwatershed has only three sites documented. Two of them are classified as moderate and one is severe. The severely eroded one is located in close proximity to the lake.

Enfield Creek - There were 52 sites in this subwatershed documented for their erosion. Most of them are classified as moderate. Eleven of them are severe. There are three classified as very severe with a steep gradient along the road.

Fall Creek - The largest of the subwatersheds, Fall Creek has many sites documented for their roadbank erosion. Most of them are moderate, but quite a few are considered to be severe. Two sites were classified as very severe.

Fish Kill - The roadbank erosion in this subwatershed is fairly moderate given the number of sites classified and the relative size of the subwatershed. Most sites documented are considered to be moderate, but there are eight sites classified as severe.

Glen/Dean Creeks Area - A few road ditches in this area are classified as moderate. There are no severe or very severe sites. However, three of the moderate sites are located near the lake shoreline.

Glenwood Creek Area - There are a number of sites documented for their roadbank erosion in this subwatershed. Most of them are classified as moderate. Three are classified as severe, all of which are located on the shoreline.

Great Gully - Most of the sites are classified as moderately eroded. One is severe. One is very severe.

Groves/Powell Creeks Area - There are a few sites classified as moderate, but no sites were severe or very severe.

Gulf Creek - There are a few sites documented as moderate, all clustered in the middle of the subwatershed.

Hicks Gully - Only five sites are classified as moderate in this fairly large subwatershed.

Interlaken Area - This large drainage area had numerous sites documented for the roadbank erosion, most of which were classified as moderate. There are seven sites designated as severely eroded, and most of these sites were located near the lake. There is one site on the lakeshore classified as very severe.

King Ferry Station Area - This drainage area has some significant erosion along the shoreline of the lake. There were numerous sites found to be moderately eroded, and a few classified as severe. Along the northern part of this subwatershed there are seven sites classified as very severe.

Lake Ridge Point Area - This drainage area has many roadbank sites classified as moderately eroded, some in close proximity to the lake. One site is classified as severe.

Lansing Area - This small subwatershed has some significant roadbank erosion problems. There are a few sites documented as moderately eroded and four severely eroded - two of which were located on the lakeshore. The concern in this area is the northwestern corner. There is a cluster of very severe road ditches located near the lakeshore.

Lavanna Area - This small subwatershed had only a few sites eroded enough to be classified as moderate. This area doesn’t have any significant problems contributing to the sediment load emptying into the lake.

Little Creek Area - A few sites are classified as moderately eroded. Two sites are severe.

Little Salmon Creek - The northern half of this subwatershed has little to no problems with roadbank erosion. However, problems have been documented in the southern portion of this area. Five sites are classified as severely eroded. There were two sites classified as very severe.

Locke Creek - There are numerous sites documented as moderately eroded throughout this area. Three sites are classified as severe and one site is classified as very severe.

McDuffie Town - There are five sites classified as moderately eroded—three of them were located on the shoreline. There is one site designated as severe.

Minnegar Creek Area - This small subwatershed has some erosion concerns considering its size. There are numerous road ditches that are moderately eroded. There are two sites classified as severe, one of them located on the lakeshore.

Paines Creek - The road ditches in this subwatershed are not heavily eroded. There are a few sites classified as moderately eroded, but there are none classified as severe or very severe.

Red Creek - This small subwatershed had only two sites documented for their roadbank erosion.

Salmon Creek - Numerous sites had moderate erosion occurring along the roadbanks throughout the subwatershed. There are a few areas classified as severe - two in the northern portion and three near the outflow to the lake. Also nearby, there is one site designated as very severe.

Schuyler Creek - This subwatershed is located in a relatively flat area. Roadbank erosion does not appear to be a significant contribution to the sediment load entering the lake. There are a few sites classified as showing signs of moderate erosion, but there are no severe or very severe sites documented.

Sheldrake Creek - Many road ditches in this subwatershed are classified as moderately eroded. One site is classified as very severe

Sixmile Creek - The roadbanks in this major subwatershed are an area of concern. There are numerous sites documented as moderately eroded. Many sites are classified as severely eroded. Eight road ditches are classified as very severe.

Spring Brook - Numerous sites are classified as moderate. Seven sites are classified as severe. None of these seven are concentrated in any one area. There are two sites designated as very severe.

Taughannock Creek - Moderately eroded roadbanks are common throughout this subwatershed. There are many severely eroded road ditches, one of which is at the mouth of Taughannock Creek. Additionally there is a site classified as very severe near the headwaters of this subwatershed.

Trumansburg Creek - There are only three sites documented for their roadbank erosion in this small watershed; however, two of them are classified as severe. These two sites are also closer to the lake than the moderately eroded site.

Union Springs Area - Numerous moderately eroded roadbanks are scattered throughout this subwatershed. All of the designated sites are concentrated in the southern half of the subwatershed.

Virgil Creek - This major subwatershed has many moderately eroded roadbanks. They are not concentrated in any one area. Nine sites are classified as severely eroded. There are no roadbanks classified as very severe, but the total number of road ditches documented for their erosion was high.

West Branch - This small subwatershed had some significant roadbank erosion There are a few areas classified as moderately eroded. Five sites are classified as severe. Two sites are classified as very severe.

Willow Creek Area - There are many sites classified as moderately eroded, but the concern is near the lakeshore where there are four sites classified as severe. A very severe road ditch is located near the lakeshore.

Yawger Creek - This area’s significant erosion is concentrated in the northern portion of the subwatershed, where three sites are classified as severe and one site is classified as very severe.

Map of Estimated Potential Roadbank Sediment by Subwatershed

Return to Wetlands, Shoreline, & Riparian Corridor Management

< <


Index


To contact the Cayuga Lake Watershed Intermunicipal Organization.

or email info@cayugawatershed.org

CLW IO 2004