## Assessing Changes to In-Stream Turb idity Following Construction of a Forest Road in West Virginia

Jingxin Wang, Pamela J. Edwards, William A. Goff 1



### A BSTRACT

Two forested headwater watersheds were monito red to examine changes to in-stream turbidity following the construction of a forest haul roa d. One watershed was us ed as an undisturbed reference, while the other had a 0.92-km (0.57-mi) ha ul road constructed in it. The channels in
both are intermittent tributaries of the Left Fork of Clover Run in the Cheat River watershed of West Virginia. To meet the objectives of another part of the study, silt fence was installed continuously along the banks of the streams from sa mpling stations at the catchments’ mouths to the headwaters of each stream network; however , the silt fence became ineffectual at and near stream crossings during road c onstruction, thereby allowing substa ntial amounts of sediment to reach the channel. Daily and stormflow samp ling began in fall 1999 using automatic collectors and continued through and beyond the period of ro ad construction which began in July 2002 and ended in September 2003. Turbidity (NTU) was m easured from those samples. Following road construction, treatment watershed turbidities incr eased significantly for bo th daily and stormflow samples. However, the increases in stormflow tu rbidities were much greater than those occurring for daily samples. Turbidity values for both dail y and stormflow samples appear to be decreasing exponentially, but neither return ed to pre-construction levels by the end of the study period.

KEYWORDS. Turbidity, Water quality, Forest road construction, Ephemeral drainages, Suspended sediment.



### I NTRODUCTION

Turbidity, the refractive index of a solution, is an indirect measure of in-stream suspended sediment concentrations (Anderson and Potts 19 87). Although, turbidity can be affected by dissolved air, solution color, particle size and sh ape, and solution concentr ation, it often is a better predictor of in-stream suspended sediment con centrations than discharge (Anderson and Potts 1987).

Road construction and use are recognized as th e primary sources of sediment production during forest operations (Hornbeck and Reinhart 1964). Roads accelerate erosion, affect run-off, and increase effective channel leng ths in headwater watersheds (R einhart 1964, Binkley and Brown 1993, Jones and Grant 1996, Wemple et al. 1996). One year after road construction in north central West Virginia, treatment watershed maximum turbidity exceeded maximum reference watershed turbidity by 3,700 Jackson turbidity un its (Hornbeck and Reinhart 1964). Turbidity increases were primarily attributed to the poor ly located skid roads and skidding in streams (Kochenderfer and Hornbeck 1999).

Roads intercept subsurface flow and precipitation, which can accelerate the transfer of hillside water to stream channels (Reinhart 1964, Wemple et al. 1996). Some road sections therefore have

1 Jingxin Wang, Associate Professor, West Virginia Univ ersity, Division of Forestry and Natural Resources, Morgantown, WV 26506, jxwang@wvu.edu. Pamela Edwards, Research Hydrologist, USDA Forest Service Northern Research Station, Parsons, WV 26287. William Goff, Research Technician, West Virginia University, Division of Forestry and Natural Resources, Morgantown, WV 26506. This is not a peer-reviewed article. TMDL 2010 Watershed Management to Improve Water Quality CD-ROM Proceedings Hyatt Regency Baltimore on the Inner Harbor, 14-17 November 2010, Baltimore, MD USA

I. Chaubey and G. Yagow eds. St Joseph Mich: ASABE
ASABE Publication Number 711P0710cdbeen classified as channel extensions -- that is, they drain intercepted pr ecipitation and subsurface water directly into a stream channel. Channel le ngths have increased up to 40 percent due to these road and stream linkages (Wemple et al. 1996). Ei ghty-eight percent of road run-off emptied into ephemeral/intermittent streams in western Wash ington and Oregon (Bilby et al. 1989). These processes can directly and indir ectly affect the quality of st reamflow by increasing sediment supply to streams, increasing in-stream sedime nt and turbidity, reducing channel storage, decreasing channel stability, and affecting storm streamflow responses (Hornbeck and Reinhart 1964, Cornish 2001, Wemple et al. 1996).

The largest increases to in-stream suspende d sediment and turbidity occur during road construction and maintenance (Hornbeck and Re inhart 1964, Swift 1988). During and one year following construction, streamflow becomes turbid more frequently, where more than fivefold increases in in-stream suspended sediment and turbidity have been reported (Hornbeck and Reinhart 1964, Fredriksen 1970). Turbidity and sedi ment tend to decrease most rapidly within the first two years post-treatment (Rice and Wallis 1962, Hornbeck and Reinhart 1964, Megahan and Kidd 1972). After a few years, recovery rates d ecrease and elevated turbidity and sediment may persist for years (Hornbeck and Reinhart 1964).

The adverse effects caused by increasing in-stream sediment have initiated the use of better construction practices. For example, best ma nagement practices (BMPs) are mandated by the 1977 Clean Water Act and state law during forest operations. Water quality degradation following forest operations decreases with the use of th e better construction practices (Kochenderfer and Hornbeck 1999). Although these methods do decreas e to-stream sediment transport, inadequate background sampling can mischaracterize BMP ef fectiveness (Edwards et al. 2004). Storm sampling is required to characterize sediment and tu rbidity in steep headwater stream channels, as variation between storm exports can be as large as or larger than variation between annually exported sediment values (Kochenderfer et al. 1997).

Turbidity is a common water quality parameter used to assess water quality in the East. West Virginia water quality regulations permit no more than a 10 NTU increase from baseline
conditions when the baseline turb idity is 50 NTU or less, which characterizes most headwater channels in Appalachian forested watersheds.. Ther efore, the objectives of this study were to: 1) describe turbidity before and after haul road construction, 2) determine if or when in-stream turbidity levels decreased after c onstruction of a haul road in th e treatment watershed, and 3) if possible, given the short pre- and post-treatment peri ods, evaluate the pattern of recovery in stream water quality.



### M ATERIALS AND METHODS

Study Background and Design

This study adopts the paired watershed design (e .g. reference and treatment watersheds) to
evaluate the effects of road construction on wate r quality (Hewlett and Pienaar 1973). Both the
reference and treated watershe ds are located within the Cl over Run watershed, Monongahela National Forest, north central West Virginia. The reference watershed is 20.2 ha, and the treatment is 32.7 ha. Their respective channel lengths, in cluding ephemeral headwaters are 905 m and 1265

m.

The analyses described in this paper are part of a larger study primarily aimed at quantifying sediment delivery to headwater channels in mana ged and unmanaged watersheds. As a result, silt
fence was installed to line the entire stream netw ork in each watershed to eliminate hillside contributions of sediment (Stedman 2008). Ho wever, during the period of road construction (described later), the silt fence in the three stre am crossings and their ap proaches were overtopped or knocked down by the construction of the crossi ngs and adjacent fillslope construction. During this period, based on sediment stored in check da ms installed downstream of the crossings, severaltons of sediment were estimated to have re ached the channel in th e treated watershed by mechanical means or by water-driven erosion and dry ravel. Prior to road construction, turbidity
measurements were made to examine in-stream c ontributions of sediment. Once road construction began and the silt fence was temporarily rende red ineffectual, the objectives of in-stream monitoring shifted to examine the effects of th ese stream crossing inputs of sediment to the
channel.

Sample Collection

Stream sampling stations were constructed at th e outlets of both watersheds in fall 1999. Automatic samplers were used to collect daily streamflow and stormflow samples throughout each storm event. Samples collected each day, or routine samples, were collected with an American Sigma model 900 automatic sampler in each wate rshed; while most of these samples were collected during nonstorm periods, the timing of some routine samples coincided with storm events. Stormflow samples were collected with an ISCO model 2700 auto matic sampler in each watershed. The ISCO samplers were actuated us ing precipitation rather than stage, and then sampled on pre-set time intervals to obtain a thorough representati on of turbidity behavior during storms (Edwards and Owens 1995).

In the treatment watershe d, the stream reach used for sample collection had a bedrock bottom. Because of the presence of bedrock substrate, se diment did not accumulate in the sampling area and the samplers did not pick up sediment from th e stream bottom. Therefore, turbidity values measured in the treatment watershed were those pres ent in the water column. By contrast, a more
stable control reach was construc ted in the reference watershed, which included a pool area, such that during drier periods, the pool collected some sediment which resulted in some artificially elevated turbidity levels in samples collected during those periods. Samples known to be substantially affected by streambed sediment accumulations were removed from the reference watershed data set. All water samples were proc essed for turbidity at the USDA Forest Service’s Timber and Watershed Laboratory in Parsons, West Vi rginia. Turbidity, in nephelometric turbidity units (NTU), was determined using a Hach ra tio turbidimeter, which was calibrated using formazin standards (Edwards et al. 2009).

Water sampling began November 2, 1999 and conti nued through June 4, 2002 in both watersheds. At that time, haul road constr uction began in the treatment wate rshed. Sampling was suspended in both watersheds at that time, and then restarted for storms on October 15, 2002 and for routine samples May 29, 2003 in the treatment watershed. Stormflow and routine sampling, respectively, were restarted on November 1, 2002 and May 2 9, 2003 in the reference watershed. Sampling continued in both watersheds through Apr il 30, 2005. The pretreatment period for both watersheds includes the time prior to haul road construction, and the post- treatment period extends from the restart of sampling in 2002 to the last sample collected. Eighty storms were sampled during pretreatment. Of these 46 were paired st orms – that is, they were sampled on both the treatment and reference watershed. Eighty-five st orms were sampled during post-treatment, and 42 were paired storms.

Road Construction

Haul road construction began in the treated watershed on July 8, 2002. The road was a cut-and-fill type of road with three culverte d stream crossings. A few days before road construction began, the silt fence in the proposed crossing areas was cu t and removed to ease culvert installation. However, the road construction contractors deta ched an additional length of the upstream and
downstream sections of the silt fence on the left a nd right sides of the stream at each crossing just before construction of each crossing began. They did this because they were concerned about damaging or covering the silt fence in the cros sing approaches during fillslope construction. Consequently, soil could reach the stream within the lengths of th e fillslope approaches where the
silt fence had been removed. The silt fence was r econstructed along the channel at the first streamcrossing on October 1-2, 2002, and at the second and third stream crossings on April 10, 2003. Silt fence was never installed across the upstream or downstream faces of the crossings, so the crossings themselves remained the primary sources of hillside sediment to the stream after silt
fence reconstruction.

The 0.92-km long road was pioneered (i.e., roug hed in) in 2002, but it was not completed until later summer 2003. During pioneering, the stream crossings were completed only to the degree needed to allow equipment to access the portions of the road further out the watershed. From July 23-25, 2002, a pair of undersized temporary culverts were placed side-by-side in the first stream crossing and partially backfilled to allow heavy equipment to travel over them. These were removed on September 4, 2002 and replaced with a singl e, larger diameter permanent culvert. No temporary culverts were insta lled in the second and third stre am crossings, and the permanent
culverts in each were instal led September 9-10, 2002 and Septem ber 12-13, 2002, respectively.

The fills over the three stream crossings and fills lopes in the approaches remained unvegetated over the 2002/2003 winter. The crossings we re hydroseeded on May 7, 2003, followed by an application of chopped mulch. Reasonably th ick grass and herbaceous vegetation became established relatively quickly. In late summer 2003, the road was su rfaced with limestone gravel.

Statistical Analyses

Statistical analyses primarily i nvolve pretreatment vs. post-treatm ent comparisons of turbidities within watersheds. Because multiple stream water samples were collected during storm events, for the stormflow samples, the value used to exam ine the influence of stream crossing construction was the maximum change in turbidity (i.e., th e difference between th e background and largest turbidity values encountered during the storm).

Statistical Analysis Systems (SAS Institute 1988) software was used to perform the statistical comparisons. Nonparametric methods primarily we re used because the data were not normally distributed. Wilcoxon two-sample tests and m ean scores (Proc NPAR1WAY) were used to
transform the data to an ordinal scale and test for statistical differences in watershed turbidity between treatment periods.



### R ESULTS

Routine Sampling

Turbidity levels in the routine samples collected during the pretreatment period in the reference watershed averaged 4.0 NTU, and had a standard deviation of 6.5 NTU (Table 1). Twenty samples exceeded 25 NTU and two samples exceeded 50 NTU (86 and 96 NTU) during the pretreatment period. Of these >25 NTU samples, only the sample with a turbidity of 96 NTU was collected during a storm event, wh ich occurred in March 2002.

Table 1. Descriptive statistics and nonparamet ric statistical comparisons between treatment periods for routine turbidity samples. Watershed Period N Turbidity (NTU)

Mean Std. Dev. Wilcoxon mean
score*

Pretreatment 1128 4.0 6.5 712 a Reference

Post-treatment 512 9.0 21.1 1038 b

Pretreatment 1110 1.6 5.0 588 a Treatment

Post-treatment 463 7.2 12.1 1264 b

*Within watersheds, values followed by different le tters are significantly different at alpha=0.05.Pretreatment routine samples in the treatment watershed averaged 1.6 NTU, with a standard deviation of 5.0 NTU (Table 1). Only 2 samples exceeded 25 NTU (61 and 147 NTU) during the pretreatment period. Both of these were colle cted during periods of very low streamflow.

Post-treatment reference watershed routine samp les averaged 9.0 NTU, with a 21.1 NTU standard deviation (Table 1). Forty samples exceeded 25 NT U. Thirty-five of the 40 samples occurred in July-September 2004. Twenty samples exceeded 50 NTU and three samples exceeded 100 NTU (102, 154, and 345 NTU). Fifty percent of the samp les that were >25 NTU occurred during very low streamflow, including the three samples gr eater than 100 NTU, which fell within a 30-day period in August-September 2004.

Treatment watershed routine samples averaged 7.2 NTU following road construction, with a standard deviation of 12.1 NTU (Table 1). Th irteen samples exceeded 25 NTU, six exceeded 50 NTU, and three samples exceeded 100 NTU (107 , 111, and 123 NTU). Seven percent of the turbidities >25 NTU were sampled during very low streamflow.

Before road construction, the tr eatment watershed routine turbidities were significantly lower than
the reference watershed routin e turbidities based on Wilcoxon mean scores (905 vs. 1330; P<0.0001). After road construction, the routine turbiditie s increased on the treated watershed so
that the Wilcoxon mean score for the treatment watershed became greater than that of the reference watershed (528 vs. 451; P<0.0001).

The largest turbidities consistently occurred duri ng the summer months in both watersheds. The average treatment watershed turbidity for May-September 2003 was 12.8 NTU, which was 5.6 times greater than the pretreatment level (2.3 NTU). The treatment watershed 2004 post-treatment mean (5.7 NTU) was 2.5 times the pretreatment level. The May through September mean decreased 2.2 times from 2003 to 2004 (Table 2).

Table 2. Changes to post-treatment May th rough September mean turbidity relative to

pretreatment May through September mean turbidity for the treatment watershed.

Pretreatment Year 2003 PostTreatment Year 2004 PostTreatment

Treatment watershed MaySeptember 2.3 NTU 12.8 NTU 5.7 NTU

Increase from pretreatment

mean 5.6 times 2.5 times

Decrease from year 2003 posttreatment mean 2.2 times

Stormflow Sampling

Reference watershed stormflow samples during pret reatment had a mean maximum increase of 19 NTU (i.e., difference between background and ma ximum storm turbidity), with a standard deviation of 22 NTU (Table 3). Treatment wate rshed stormflow samples during pretreatment had a mean maximum increase of 27 NTU, with a standard deviation of 59 NTU (Table 3).

Post-treatment, the reference watershed stormflo w samples had a lower mean maximum increase of 14 NTU, with a standard de viation of 22 NTU (Table 3). Pre- and post-treatment Wilcoxon mean scores were not significantly different for the reference watershed. By contrast, treatment watershed stormflow samples following road c onstruction had a mean maximum increase of 182 NTU, with a standard deviation of 384 NTU (Table 3). The post-treatment maximum increase was 6.7 times higher than the pretreatment increase on the roaded watershed, and the Wilcoxon mean scores were significantly different.Table 3. Descriptive statistics and nonparamet ric statistical comparisons between treatment periods for maximum change in turbidity for each storm. Watershed Period N Change in turbidity (NTU)

Mean Std. Dev. Wilcoxon mean
score*

Pretreatment 54 19 22 60 a Reference

Post-treatment 58 14 18 53 a

Pretreatment 72 27 59 55 a Treatment

Post-treatment 69 182 384 88 b

*Within watersheds, values followed by different letters are significantly different at alpha=0.05.

Over time, the treatment watershed showed an improving trend with first and second year posttreatment mean maximum turbidity increases duri ng sampled storms continuing to decline (Fig. 1); however, the turbidity in the roaded waters hed remained elevated at the end of the study compared to turbidities encountered prior to road constr uction. These available short-term results suggest that stormflow turbiditie s are returning to pretreatment conditions via an exponential decay pattern (Fig. 1).

Pretreatment Construction 1st Year Post-treat 2nd Year Post-treatMean maximum change in turbidity (NTU)

0 50 100 150 200 250 300

Reference

Treatment

Figure 1. Mean maximum ch ange in turbidity for st orm events by watershedand treatment period. Construction = July 8, 2002-Sept. 2003; 1st Year Posttreat = Oct. 2003-Sept. 2004; 2nd Year Post-treat = Oct. 2004-April 2005.



### C ONCLUSIONS

The reference watershed routine (i .e., daily) samples in the pretre atment period were statistically more turbid compared to the treatment watershe d. However, prior to road construction, both
watersheds had mean turbidities below 5 NTU. Tu rbidity is visible to the human eye at about 5 NTU (Strausberg 1983); therefore, these streams nor mally run clear during baseflow. While there were statistically signifi cant increases in routine sample tu rbidity following road construction, they were relatively small compared to change s that occurred during stormflow. The average change between background and peak turbidities during storms rose from 14 NTU prior to road construction to 182 NTU following road construction.

Over time, both the routine and stormflow turbidity levels declined exponen tially, but they did not return to pretreatment conditions by the end of the study period. The majority of the sediment inputs were from the stream crossing areas and th eir approaches, but as the fillslope inputs of sediment were restricted by silt fence reconstruction and the remaining crossing fills became revegetated, sediment inputs declin ed. Long-term turbidity increases over pretreatment level will
be attributable to residual sedi ment inputs from the construction that have been stored in the channel and are flushed out periodically.

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