4. Instrumentation

Instrumentation was planned to achieve the general objectives listed above under natural precipitation and weather conditions—small scale evaluations of treatments, evaluations of watershed responses at larger scales, and "modeling." Generally, instrumentation for measuring watershed responses to treatments was to be permanently available for experiments. This allowed the immediate use of experimental watersheds with a long runoff record to be used in comparisons when evaluating land treatments and reduced the cost of monitoring runoff.

Small watersheds, ranging in size from 0.26 to 3.07 ha, were installed on the smaller 425-ha area (Figure 2 right) in natural-swale, ephemeral, overland-flow areas on the hillsides where runoff occurs during large intensity rains and snowmelt. These watersheds were used as "test beds" to determine the effectiveness of different land-management treatments. The treatment for an individual watershed was implemented over the entire area so that runoff-response data were not confounded by runoff from other areas with different land managements. Runoff from the smaller watersheds were measured using H flumes ([6], Figure 4). More recently, two watersheds were monitored using drop-box weirs which provide better flow measurement in sediment-laden runoff water [7], (Figure 5). Because of spatial variability of precipitation, each watershed was instrumented with a weighing-bucket rain gauge. Runoff and precipitation data were historically tabulated with depth and time resolutions of 0.25 mm and 1 min, respectively, and when a change in flow depth or precipitation intensity was apparent. Larger watersheds on the 425-ha area up to 123 ha were monitored using Parshall flumes initially and later short-crested V-notch weirs replaced them [6], (Figure 6).

large as 15 ha have been monitored by using springs because of this favorable geological structure. Impacts of land management on ground water became a significant area of

2. Nonuniform runoff generation [2]. Due to springs at the ground surface and persistently high soil-profile-water-content areas, runoff is generated nonuniformly on the surface and with time during an event. NAEW measurements of natural-precipitation infiltration showed that water simultaneously emerges from the soil (exfiltration) and infiltrates into it during a runoff event at different locations. Watershed models today are deficient in modeling this runoff-generating process. Superimposed on these physical processes are wide ranging anthropogenic influences on the land surface as watershed areas increase that also help to

3. Interflow process [2]. Closely related to nonuniform runoff generation is the interflow process in which water moves laterally within the soil profile. This process was apparent

4. Natural lysimeter [2]. A lysimeter (discussed under "Instrumentation" section) is usually considered an isolated block of soil that accounts for the sources and distribution of water in a contained area. It was discovered that a thick clay layer underlying a coal seam outcropped along the periphery of a hilltop enclosed an approximate area of 2.8 ha (known as Urban's Knob). The synclinal structure of the sedimentary bedrock within the hilltop forced all water entering the hilltop to its center where it discharged to a surface spring. Consequently, the source of all water within the hilltop was from precipitation as no ground water flowed from adjacent areas as often occurs in ground-water studies, forming a "natural" lysimeter. The area was instrumented with a network of wells and piezometers, a spring, two watersheds, a rain gauge, and profiles of ceramic suction cup

5. Macropore flow [2]. There is significant transport of chemicals and water in larger pores in the soil (particularly holes caused by earthworms), a poorly simulated process in watershed models. This became a significant area of research at the NAEW as explained later.

Instrumentation was planned to achieve the general objectives listed above under natural precipitation and weather conditions—small scale evaluations of treatments, evaluations of watershed responses at larger scales, and "modeling." Generally, instrumentation for measuring watershed responses to treatments was to be permanently available for experiments. This allowed the immediate use of experimental watersheds with a long runoff record to be used in comparisons when evaluating land treatments and reduced the cost of monitoring runoff.

Small watersheds, ranging in size from 0.26 to 3.07 ha, were installed on the smaller 425-ha area (Figure 2 right) in natural-swale, ephemeral, overland-flow areas on the hillsides where

on the NAEW and is also not well simulated in watershed models (Figure 3).

lysimeters to investigate unsaturated flow of water and chemicals.

research on the NAEW.

6 Hydrology of Artificial and Controlled Experiments

4. Instrumentation

generate runoff nonuniformly over a landscape.

The LMC watershed was instrumented with a network of recording rain gauges and weirs (Figure 2, left). Nested watersheds ranged in size from approximately 39 to 1854 ha. As mentioned before, LMC was closed in about 1970 so there is approximately 30 years of runoff and precipitation data available from most of these watersheds and rain gauges. These watersheds were useful for documenting the nonlinearity of runoff ("scaling," Figure 7) at Coshocton, and have potential for other investigations such as for regional model parameterization and routing.

Figure 4. H flume and original Coshocton wheel rotating-slot sampler.

Figure 5. Turbulent flow in a NAEW drop-box weir for flow measurement in sediment-laden runoff.

Figure 6. Short-crested V-notch weir replaced the Parshall flume upstream in the view on a larger NAEW watershed.

While small watersheds provided data on runoff responses at a small watershed scale, the originators of the experimental watershed program wanted to investigate on a very small scale the water balance on isolated blocks of undisturbed soil ("monolith lysimeters," Figures 8 and 9). Eleven lysimeters were installed in the three dominant soil types on the NAEW, four each on two soil types and three on the third soil type. Each lysimeter had a horizontal surface area of ~0.0008 ha (width ~1.8 m and length ~4.3 m), depth was ~2.4 m, and enclosed an undisturbed monolith of the soil profile. The 2.4-m depth included undisturbed surface soil and weather bedrock. Each lysimeter measured percolation (ground-water recharge) from

Figure 8. Construction and installation of three lysimeters at the NAEW.

Figure 7. Watershed area versus annual runoff for different physiographic locations in the USA. Graph from [8, 9].

Experimental Watersheds at Coshocton, Ohio, USA: Experiences and Establishing New Experimental Watersheds

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9

Figure 7 shows how watersheds in different physiographic and climatological regions in the USA respond to climate as watershed area increases. For the unglaciated watersheds in the Coshocton area, the nonlinearity of watershed area vs. runoff relationship reflects the increase in baseflow to a relatively constant value as more and larger stream channels intersect perched water tables in this region of sedimentary strata (dashed line in Figure 3).

Experimental Watersheds at Coshocton, Ohio, USA: Experiences and Establishing New Experimental Watersheds http://dx.doi.org/10.5772/intechopen.73596 9

Figure 7. Watershed area versus annual runoff for different physiographic locations in the USA. Graph from [8, 9].

Figure 8. Construction and installation of three lysimeters at the NAEW.

Figure 7 shows how watersheds in different physiographic and climatological regions in the USA respond to climate as watershed area increases. For the unglaciated watersheds in the Coshocton area, the nonlinearity of watershed area vs. runoff relationship reflects the increase in baseflow to a relatively constant value as more and larger stream channels intersect perched

Figure 6. Short-crested V-notch weir replaced the Parshall flume upstream in the view on a larger NAEW watershed.

water tables in this region of sedimentary strata (dashed line in Figure 3).

Figure 5. Turbulent flow in a NAEW drop-box weir for flow measurement in sediment-laden runoff.

8 Hydrology of Artificial and Controlled Experiments

While small watersheds provided data on runoff responses at a small watershed scale, the originators of the experimental watershed program wanted to investigate on a very small scale the water balance on isolated blocks of undisturbed soil ("monolith lysimeters," Figures 8 and 9). Eleven lysimeters were installed in the three dominant soil types on the NAEW, four each on two soil types and three on the third soil type. Each lysimeter had a horizontal surface area of ~0.0008 ha (width ~1.8 m and length ~4.3 m), depth was ~2.4 m, and enclosed an undisturbed monolith of the soil profile. The 2.4-m depth included undisturbed surface soil and weather bedrock. Each lysimeter measured percolation (ground-water recharge) from

the desirability of using a drop-box weir that will keep sediment moving through the flume

Experimental Watersheds at Coshocton, Ohio, USA: Experiences and Establishing New Experimental Watersheds

http://dx.doi.org/10.5772/intechopen.73596

11

In the 1970s, water quality beyond sediment concentrations became important [3]. Pesticides, major anions and cations, and nutrient losses, especially nitrogen, from the small watersheds became a concern and various land management treatments were evaluated using these measures as well as runoff volumes and sediment loads, and subsurface flow. The Coshocton Wheel provided the sample needed for laboratory analyses of these constituents and loads

Occasionally, new watershed and plots sites on and off the NAEW were required such as for coal surface-mine (Figure 11), paper-mill byproduct, and manure studies. NAEW scientific

The small NAEW experimental watersheds were managed with a new treatment following an old one on the same watershed. This allowed comparisons of current treatments with previous

Figure 10. H flume and downstream sediment trough that catches all sediment from the bare, steep watershed after an

Figure 11. NAEW scientists investigated the effects of drastic land disturbances due to surface mining for coal before and

during mining, and after reclamation on ground and surface water hydrology and water quality.

were similarly computed as for sediment concentrations.

and technical personnel provided the needed expertise.

ones. Occasionally, a paired watershed approach was used.

(Figure 5).

extreme event.

Figure 9. Schematic profile of an underground weighing lysimeter with and undisturbed profile of weathered bedrock near the bottom and soil at the top.

the bottom and runoff from the surface. Additionally, one lysimeter at each set of lysimeters within a soil type was weighed to provide evapotranspiration and ground-level precipitation data.

Recognizing the spatial variability of precipitation over small areas (especially during summer months), precipitation data were monitored by using weighing-bucket rain gauges with orifices placed approximately 1 m above the ground at most small watersheds. Gauges were similarly placed at each of the three sets of lysimeters.

Weather data were measured at a single weather station on the NAEW and included wind speed and direction, air temperature, humidity, solar radiation, evaporation pan, barometric pressure, soil temperature, and precipitation. Since about 1985, data loggers were used to monitor all NAEW data (except precipitation) with a radio-telemetry system. This system allowed more frequently measured weather, runoff, and precipitation data to be recorded. Prior to ~1985, runoff and other charts were hand tabulated. For the entire period, manual measurements were made of some weather elements.

Soil loss from the small experimental watersheds was an original concern; however, no reliable water sampler was available to measure sediment concentration during a runoff event. Consequently, the "Coshocton Wheel" was invented in about 1945 to obtain a flow-weighted composite measurement of the total sediment concentration during runoff events (Figure 4). The sampler consisted of a water (runoff)-powered wheel with a rotating slot (no power requirements), and obtained a constant fraction of the total sediment load from the watershed (single sample). The sampler has been used worldwide. When event concentration is multiplied by total runoff, an estimate of event sediment load is obtained for the treatment on the small watershed. Prior to the NAEW invention of the Coshocton Wheel, all runoff and sediment were collected in concrete troughs that were dug out manually to obtain a measurement of sediment yield (Figure 10). Note that the flume is full of sediment after the runoff event flowed over the bare, steep soil. This photo demonstrates the need for an automatic water sampler and the desirability of using a drop-box weir that will keep sediment moving through the flume (Figure 5).

In the 1970s, water quality beyond sediment concentrations became important [3]. Pesticides, major anions and cations, and nutrient losses, especially nitrogen, from the small watersheds became a concern and various land management treatments were evaluated using these measures as well as runoff volumes and sediment loads, and subsurface flow. The Coshocton Wheel provided the sample needed for laboratory analyses of these constituents and loads were similarly computed as for sediment concentrations.

Occasionally, new watershed and plots sites on and off the NAEW were required such as for coal surface-mine (Figure 11), paper-mill byproduct, and manure studies. NAEW scientific and technical personnel provided the needed expertise.

The small NAEW experimental watersheds were managed with a new treatment following an old one on the same watershed. This allowed comparisons of current treatments with previous ones. Occasionally, a paired watershed approach was used.

the bottom and runoff from the surface. Additionally, one lysimeter at each set of lysimeters within a soil type was weighed to provide evapotranspiration and ground-level precipitation

Figure 9. Schematic profile of an underground weighing lysimeter with and undisturbed profile of weathered bedrock

Recognizing the spatial variability of precipitation over small areas (especially during summer months), precipitation data were monitored by using weighing-bucket rain gauges with orifices placed approximately 1 m above the ground at most small watersheds. Gauges were

Weather data were measured at a single weather station on the NAEW and included wind speed and direction, air temperature, humidity, solar radiation, evaporation pan, barometric pressure, soil temperature, and precipitation. Since about 1985, data loggers were used to monitor all NAEW data (except precipitation) with a radio-telemetry system. This system allowed more frequently measured weather, runoff, and precipitation data to be recorded. Prior to ~1985, runoff and other charts were hand tabulated. For the entire period, manual

Soil loss from the small experimental watersheds was an original concern; however, no reliable water sampler was available to measure sediment concentration during a runoff event. Consequently, the "Coshocton Wheel" was invented in about 1945 to obtain a flow-weighted composite measurement of the total sediment concentration during runoff events (Figure 4). The sampler consisted of a water (runoff)-powered wheel with a rotating slot (no power requirements), and obtained a constant fraction of the total sediment load from the watershed (single sample). The sampler has been used worldwide. When event concentration is multiplied by total runoff, an estimate of event sediment load is obtained for the treatment on the small watershed. Prior to the NAEW invention of the Coshocton Wheel, all runoff and sediment were collected in concrete troughs that were dug out manually to obtain a measurement of sediment yield (Figure 10). Note that the flume is full of sediment after the runoff event flowed over the bare, steep soil. This photo demonstrates the need for an automatic water sampler and

similarly placed at each of the three sets of lysimeters.

measurements were made of some weather elements.

data.

near the bottom and soil at the top.

10 Hydrology of Artificial and Controlled Experiments

Figure 10. H flume and downstream sediment trough that catches all sediment from the bare, steep watershed after an extreme event.

Figure 11. NAEW scientists investigated the effects of drastic land disturbances due to surface mining for coal before and during mining, and after reclamation on ground and surface water hydrology and water quality.
