Wesley C. Wright

EVALUATION OF METHODS FOR ESTIMATING DAILY REFERENCE CROP EVAPOTRANSPIRATION AT A SITE IN THE HUMID SOUTHEAST UNITED STATES

Estimated daily reference crop evapotranspiration (ETo) is normally used to determine the water requirement of crops using the crop factor method. Many ETo estimation methods have been developed for different types of climatic data, and the accuracy of these methods varies with climatic conditions. In this study, pair-wise comparisons were made between daily ETo estimated from eight different ETo equations and ETo measured by lysimeter to provide information helpful in selecting an appropriate ETo equation for the Cumberland Plateau located in the humid Southeast United States. Based on the standard error of the estimate (Syx), the relationship between the estimated and measured ETo was the best using the FAO-56 Penman-Monteith equation (coefficient of determination (r2) = 0.91, Syx = 0.31 mm d-1, and a coefficient of efficiency (E) = 0.87), followed by the Penman (1948) equation (r2 = 0.91, Syx = 0.34 mm d-1, and E = 0.88), and Turc’s equation (r2 = 0.90, Syx = 0.36 mm d-1, and E = 0.88). The FAO-24 Penman and Priestly-Taylor methods overestimated ETo, while the Makkink equation underestimated ETo. The results for the Hargreaves-Samani equation showed low correlation with lysimeter ETo data (r2 = 0.51, Syx = 0.68 mm d-1, and E = 0.20), while those for the Kimberly Penman were reasonable (r2 = 0.87, Syx = 0.40 mm d-1, and E = 0.87). These results support the adoption of the FAO-56 Penman-Monteith equation for the climatological conditions occurring in the humid Southeast. However, Turc’s equation may be an attractive alternative to the more complex Penman-Monteith method. The Turc method requires fewer input parameters, i.e., mean air temperature and solar irradiance data only.

Increasing exfiltration from pervious concrete and temperature monitoring.

Pervious concrete typically has an infiltration rate far exceeding any expectation of precipitation rate. The limiting factor of a retention based pervious concrete system is often defined by how quickly the underlying soil subgrade will infiltrate the water temporarily stored within the concrete and/or aggregate base. This issue is of particular importance when placing a pervious concrete system on compacted fine textured soils. This research describes the exfiltration from twelve pervious concrete plots constructed on a compacted clay soil in eastern Tennessee, USA. Several types of treatments were applied to the clay soil prior to placement of the stone aggregate base and pervious concrete in an attempt to increase the exfiltration rate, including: 1) control--no treatment; 2) trenched--soil trenched and backfilled with stone aggregate; 3) ripped--soil ripped with a subsoiler; and 4) boreholes--placement of shallow boreholes backfilled with sand. The average exfiltration rates were 0.8 cm d(-1) (control), 4.6 cm d(-1) (borehole), 10.0 cm d(-1) (ripped), and 25.8 cm d(-1) (trenched). The trenched treatment exfiltrated fastest, followed by the ripped and then the borehole treatments, although the ripped and borehole treatments were not different from one another at the 5% level of significance. The internal temperature of the pervious concrete and aggregate base was monitored throughout the winter of 2006-2007. Although the temperature of the pervious concrete dropped below freezing 24 times, freezing concrete temperatures never coincided with free water being present in the large pervious concrete pores. The coldest recorded air temperature was -9.9 degrees C, and the corresponding coldest recorded pervious concrete temperature was -7.1 degrees C. The temperature of the pervious concrete lagged diurnal air temperature changes and was generally buffered in amplitude, particularly when free water was present since the addition of water increases the thermal capacity of the pervious concrete greatly. The temperature of the aggregate base was further buffered to diurnal changes, and no freezing temperatures were recorded.

DESIGN AND EVALUATION OF AN IMPROVED FLOW DIVIDER FOR SAMPLING RUNOFF PLOTS

An improved flow divider was designed to simplify and lower the cost of collecting runoff data from research plots. The system was designed around commercially available and inexpensive 5-gal (19-L) plastic buckets with screw top lids. A precision cut sheet-metal divider “crown” is fastened to the lid, allowing it to be easily transferred between buckets. The divider crown can be configured to handle various flow rates by specifying the number of flow divisions. Laboratory evaluation of the design indicated that the system divides runoff with accuracies within .5% over most of the flow range and within .15% at very low and very high flows. These results are similar to those found for the more traditional flow divider designs. Adding sediment to the inflow at three different flow rates yielded sediment division accuracies within 7%. Five field research projects have used the divider system with few problems. The average cost of this system is approximately US

SEAL FORMATION BENEATH ANIMAL WASTE HOLDING PONDS

500 per plot, in comparison to the US

CALIBRATION OF FIVE-SEGMENT TIME DOMAIN REFLECTOMETRY PROBES FOR WATER CONTENT MEASUREMENT IN HIGH DENSITY MATERIALS

3000 to

Curve Numbers for Low-Compaction Steep-Sloped Reclaimed Mine Lands in the Southern Appalachians

5000 it often costs to instrument a plot using standard equipment.

IDENTIFYING LONG-TERM PREFERENTIAL AND MATRIX FLOW RECHARGE AT THE FIELD SCALE

The objectives of this study were to measure the sealing effectiveness of swine and dairy waste applied to a variety of soil textures and to develop a suitable model for describing the sealing process through time. Dairy and swine waste were applied to soil columns packed with sand, silt loam, or clay. A seal developed that reduced the infiltration rates to approximately 10-6 cm s-1 or less within the 54 to 60 day testing period. Throughout the test, the infiltration rates into the clay soil were lowest. Yet as time passed, the differences between soil types diminished. Swine waste applied to sand required more time to develop a seal than all other combinations of waste and soil. A model was developed that describes cumulative infiltration as function of elapsed time, waste height, waste total solids content, and soil hydraulic conductivity. After a stable seal develops, the model predicts that only the seal properties (not the soil properties) are responsible for limiting infiltration. During the seal-dominated phase, a plot of cumulative infiltration versus the square root of time is linear, and the respective slope is dependent on a lumped parameter (Kseal/a). A review of available waste infiltration datasets from the literature revealed that Kseal/a can be estimated from the total solids concentration of the waste (R2 = 0.87). Predictions of Kseal/a were not improved by including the hydraulic conductivity of the soil into the estimate or by analyzing the dairy and swine waste datasets separately. This suggests that neither soil hydraulic conductivity nor waste type greatly affect the infiltration rate during the seal-dominated phase of infiltration.

Surface erosion and sediment yields on steep-sloped coal mining reclamation sites in the Appalachian Region.

Time domain reflectometry (TDR) is a method of measuring high-frequency signal propagation times. TDR systems are widely used for in situ measurement of soil water content. Water content is one of the principal factors that governs many soil properties and is of special significance to shallow foundation pavement systems. Water content is calculated based on the measured dielectric properties of the soil system. Originally, TDR systems for water content measurement were developed for use in soils with low bulk densities, similar to those found in agriculture. Four highway test sites in Tennessee were instrumented with five-segment TDR probes in the soil subgrade and in the unbound aggregate sub-base. These materials are denser than agricultural soils. After several months of data collection and field verification, the TDR predicted water content and gravimetric water content did not coincide. For this reason, a study was performed with the TDR equipment using each of the four test site subgrade soils and an unbound aggregate sub-base sample. Ten previously published TDR water content relationships were evaluated to determine which relationship most accurately predicted water content for the subgrade soils and for the unbound aggregate sub-base using the five-segment probe. During the course of the study, it was necessary to evaluate the manufacturers relationship between the measured propagation time and the corrected propagation time, which accounts for the epoxy fill between the probe waveguides. The relationship was revised to reduce significant variation in corrected propagation times between segments. It was found that the relationship between inverse signal velocity and soil water content proposed by Herkelrath et al. (1991) most accurately predicted water content for all subgrade soils; however, this relationship required the derivation of a soil-specific slope and intercept. The equation proposed by Baran (1994) most accurately predicted water content for the unbound aggregate sub-base. Both of these relationships appeared to provide a better prediction than the widely used Topps relationship.

IN SITU MEASUREMENT AND EMPIRICAL MODELING OF BASE INFILTRATION IN HIGHWAY PAVEMENT SYSTEMS

AbstractIn the coal-mining region of the Appalachians, the Forestry Reclamation Approach (FRA) is currently promoted by the U.S. Dept. of Interior, Office of Surface Mining (OSM). FRA’s goal in establishing native forest cover on reclamation sites requires the use of loose spoils rather than traditionally compacted spoils during hillslope reconstruction. Loose spoils improve tree planting survival and enhance overall forest growth. Although FRA has been shown to be successful on low-gradient slopes without excessive runoff leading to erosion, rainfall-runoff relationships have not been studied on steep slopes (>20°) where most surface-mine reclamation typically occurs. A curve number (CN) range representing low-compaction steep-sloped conditions was needed for Appalachian FRA sites. Three active surface-mine sites in East Tennessee were monitored during a 1-year period (June 2009–July 2010) for rainfall (5-min intervals) and runoff hydrology (discharge volume, peak discharge) using a unique Pinson-type co...

NONINTRUSIVE MAPPING OF NEAR-SURFACE PREFERENTIAL FLOW

Preferential recharge from agricultural production fields can lead to agrochemical contamination of groundwater due to short-circuiting of the soil matrix. This research determines the relative amounts of preferential and matrix flow recharge from a no-till agricultural production field. The conservative tracer potassium bromide was surface applied to a 0.37 ha bermed field plot at a rate of 900 kg ha-1 as bromide. The site was instrumented to monitor precipitation and runoff from the bermed field plot. Three years after the bromide application, twenty-one 3.65 m continuous soil cores were collected from the bermed plot and analyzed for bromide. Based solely on the shape of the bromide profiles, most of the 21 soil cores showed no apparent preferential flow. However, up to 83% of the infiltrated bromide mass was absent from individual soil cores, presumably due to preferential flow. Using a mass balance approach, we estimated that 58% of the recharge was due to preferential flow and 42% was due to matrix flow.