**3. Practice on the WHES: II–Hydrohill, an artificial catchment**

#### **3.1. The construction of Hydrohill**

The artificial catchment Hydrohill of CHL was designed by Wei-Zu Gu during 1975 while he came back from his peasant life, kindly accepted and supported by Chuzhou administrator Mr. Wu-Min Cao for the laying down of both the Hydrohill and Nandadish on 1978. NHRI completed it and start running with data collection since July, 1982. The technological process can be sketched out summarily as follows.

(1) *Site selection and clearance*: A southeastward hillslope on a small hill, which is protruding integrally outwardly from its main area was selected for our Hydrohill due to its main geologic setting of andesitic tuff with altered volcanic rock. The space of this slope is enough for our initial design including in total three sister catchments with different characters each other. Moving away all the deposits including the weathered rock until the exposure of fresh bedrock, the site of clearance with area of ca 4700 m<sup>2</sup> was then prepared, however, only one catchment was constructed; (2) *Artificial aquiclude and surrounding wall*. A concrete aquiclude with two intersecting slopes dipping toward each other at 10°, an overall downslope gradients of 14°, and the longitudinally extending rectangular drainage trench etc. are constructed following the integral design of Hydrohill (**Figure 9a**). After that, an impermeable wall was set up on this aquiclude across the catchment boundaries (**Figure 9a**) aimed at enclosing the catchment to prevent any lateral exchanges of underground flow. These were completed during 1978 with its bird's eye view shown in **Figure 9b**. (3) *Soil filling*. An agricultural land was selected for the soil source of Hydrohill, a soil profile at the agricultural site with depth ca 1.5 m below the ground surface was dug for general observations, and undistributed soil of different layers were sampled for bulk density using current method. After that, the soil of the agricultural site was started to remove from its top horizon of about 10 cm in depth; it was piled up at a place close to Hydrohill, covered and marked. Then, the deeper parts of the soil were taken layer-by-layer every 20 cm and piled up, covered, and marked again. During soil filling

in the concrete framework of Hydrohill, it was started from the soil pile of the deepest layer, that is, 90–100 cm of the original soil layer, it entered first into the artificial framework, after this layer was filling up, it was sampled for bulk density check. Then, the next piles of soil and so on. The

**Figure 9.** Constructions of Hydrohill. (a) the artificial aquiclude and surrounding wall; (b) view of the completed concrete aquiclude and wall; (c) view of the artificial catchment while soil was filled up, it was in idle for 3 years waiting for the physical improving of filling soil; (d) setting up monitoring networks for both saturated and unsaturated zone; (e) set drainage trenches; (f) the splicing fiberglass troughs and some steel supports; (g) the rectangular bottom trough for SSR100 and steel supports for the setting of SSR60 trough above it; (h) the gap for inverted filter and the nylon net in preparing; (i) the stainless steel screen in preparation for setting; (j) a curved connection trough; (k) connection troughs in installing; (l) discharge measuring structures using V-notch based logarithm sharp crested weirs (1982–1995).

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**3. Practice on the WHES: II–Hydrohill, an artificial catchment**

bottle for SR, 2-a sample bottle for SSR50, 3-a sample bottle for SSR100, 4-a safeguard bottle.

The artificial catchment Hydrohill of CHL was designed by Wei-Zu Gu during 1975 while he came back from his peasant life, kindly accepted and supported by Chuzhou administrator Mr. Wu-Min Cao for the laying down of both the Hydrohill and Nandadish on 1978. NHRI completed it and start running with data collection since July, 1982. The technological process

**Figure 8.** Water sampling in Nandadish: (a) sampling for precipitation, 1-a specially designed rain gauge capable of collecting rain samples at one-hour interval, 2-a standard rain gauge collecting the mixed sample of each rain event, 3-a tube directing rain water into a sampling bottle at the gauging room; (b) sampling for runoff components, 1-a sample

(1) *Site selection and clearance*: A southeastward hillslope on a small hill, which is protruding integrally outwardly from its main area was selected for our Hydrohill due to its main geologic setting of andesitic tuff with altered volcanic rock. The space of this slope is enough for our initial design including in total three sister catchments with different characters each other. Moving away all the deposits including the weathered rock until the exposure of fresh bedrock, the site of clearance with

*aquiclude and surrounding wall*. A concrete aquiclude with two intersecting slopes dipping toward each other at 10°, an overall downslope gradients of 14°, and the longitudinally extending rectangular drainage trench etc. are constructed following the integral design of Hydrohill (**Figure 9a**). After that, an impermeable wall was set up on this aquiclude across the catchment boundaries (**Figure 9a**) aimed at enclosing the catchment to prevent any lateral exchanges of underground flow. These were completed during 1978 with its bird's eye view shown in **Figure 9b**. (3) *Soil filling*. An agricultural land was selected for the soil source of Hydrohill, a soil profile at the agricultural site with depth ca 1.5 m below the ground surface was dug for general observations, and undistributed soil of different layers were sampled for bulk density using current method. After that, the soil of the agricultural site was started to remove from its top horizon of about 10 cm in depth; it was piled up at a place close to Hydrohill, covered and marked. Then, the deeper parts of the soil were taken layer-by-layer every 20 cm and piled up, covered, and marked again. During soil filling

was then prepared, however, only one catchment was constructed; (2) *Artificial* 

**3.1. The construction of Hydrohill**

262 Hydrology of Artificial and Controlled Experiments

area of ca 4700 m<sup>2</sup>

can be sketched out summarily as follows.

**Figure 9.** Constructions of Hydrohill. (a) the artificial aquiclude and surrounding wall; (b) view of the completed concrete aquiclude and wall; (c) view of the artificial catchment while soil was filled up, it was in idle for 3 years waiting for the physical improving of filling soil; (d) setting up monitoring networks for both saturated and unsaturated zone; (e) set drainage trenches; (f) the splicing fiberglass troughs and some steel supports; (g) the rectangular bottom trough for SSR100 and steel supports for the setting of SSR60 trough above it; (h) the gap for inverted filter and the nylon net in preparing; (i) the stainless steel screen in preparation for setting; (j) a curved connection trough; (k) connection troughs in installing; (l) discharge measuring structures using V-notch based logarithm sharp crested weirs (1982–1995).

in the concrete framework of Hydrohill, it was started from the soil pile of the deepest layer, that is, 90–100 cm of the original soil layer, it entered first into the artificial framework, after this layer was filling up, it was sampled for bulk density check. Then, the next piles of soil and so on. The workers are happy to follow our lazy filling and the time-consuming checking on depths and bulk density of whole area by paying hourly wages. After whole area was completed, it was allowed to settle for 3 years before equipped (**Figure 9c**), while the natural grasses were revitalized. We then have opportunity to remeasure the established bulk densities during first exaction for the main trench later during 1981, it is 1.44 g/cm3 at the top soil of 0–30 cm, 1.42 g/cm3 of the layer at the depth of 30–50 cm, 1.40 g/cm3 of 50–75 cm, and 1.60 g/cm3 of 75–100 cm. (4) *Setting up monitoring networks for both saturated and unsaturated zone.* Three networks including 22 wells for saturated water (groundwater) table measurements and groundwater sampling, 21 aluminum alloy access tubes for neutron moisture gauge were installed, all of them were drilled to the aquiclude (**Figure 9d**). The tubes for groundwater monitoring were slotted along the lowermost 20 cm and wrapped up by plastic net (**Figure 10a** and **b**). After installation into the drilling hole, the space around the slotted lengths were packed with sands to allow movement of groundwater to the well, however, the space above the slotted lengths should be carefully stuffed up by small dried clay balls to prevent any water other than groundwater intruding along the pipes (**Figure 10c** and **d**). Different from the tube for groundwater, the neutron access tubes should have an intact wall with sealed bottom, using threaded cap with a hanging pack of desiccant for sustaining a state of dryness in the tube (**Figure 6e**). A part of resulted networks is shown in **Figure 10d**. (5) *Drainage trenches.* After the installation of groundwater wells and access tubes, the drainage trenches including the main longitudinal trench and the side trench perpendicular to the main trench at the watershed outlet were dug up (**Figure 9e**). (6) *The layered troughs*. It was worked first from the bottom one. The splicing fiberglass troughs each 40 cm wide and some steel supports are shown in **Figure 9f**, **Figure 9g** shows the rectangular trough for SSR100 and steel supports for the setting of trough above it, that is, the SSR60. These troughs were constructed as shown in **Figure 11**, they were stacked on top of each other to create a set of long zero-tension lysimeters, each trough has a 20 cm aluminum lip that extends horizontally into the soil layer to prevent leakage between layers (**Figure 11**).(7) *The inverted filter*. There is a gap between the trough and the soil (**Figure 9h**) for the inverted filter (**Figure 11**) including the filling materials and the nylon net at the soil side and the stainless steel screen at the trough side (**Figure 9h** and **i**, **Figure 11**). (8) *The connection troughs*. With different curvatures, these troughs link the runoff troughs with the approaching part of measuring structures individually (**Figure 9j** and **k**). (9) *Discharge measuring structures.* We combined the V-notch sharp crested weir and the logarithm-notch sharp crested weir together, and defined it as the V-notch based logarithm sharp crested weir (**Figure 9l**) for discharge measurement of SR and SSRs. (10) At last, 30 hole sites for tensiometers at different depths together with the connection tubes from tensiometer to the scanning recorder were set up (**Figure 10e**).

After the finalization of construction, the artificial Hydrohill catchment has a drainage area of 490 m<sup>2</sup> (horizontal projection), 512 m<sup>2</sup> (inclined surface) as shown in **Figure 12** including its previous version since 1982 (**Figure 12a–d**), and the renovation version (**Figure 12e**–**h**). The lengths of the longitudinal trough (5 in **Figure 12b**, **c**, **e**, **g**) and the transverse trough (4 in **Figure 12b** and **e**) are 29.4 and 6.8 m, respectively. The width of the trough is 0.4 m. The horizontal projected area of the trough is 13.8 m<sup>2</sup> , and thus horizontal projected area of soil surface is 487.2 m<sup>2</sup> .

**3.2. Instrumentation in Hydrohill catchment**

gauge and the tensiometer with connection plastic tubes to the scanner.

To monitor the distribution of rainfall and test the spatial uniformity of the rainfall generated by a rainfall simulator, 12 standard rain gauges (**Figure 14a** and **b**) and 5 tipping bucket

**Figure 11.** Construction of troughs. SR-trough for surface runoff; SSR30-trough for subsurface runoff at the depth of

30 cm below the ground surface; SSR60-that at the depth of 60 cm; SSR100-that at the depth of 100 cm.

**Figure 10.** Construction of groundwater monitoring well. (a) the slotted part of steel tube; (b) the tube was wrapped up by plastic net; (c) making clay balls for using; (d) during installing, the space between the tube and drilling hole above the slotted lengths (shown by a yellow arrow) should be carefully stuffed up by small dried clay balls using a special designed tool. This picture is shown in commemoration of the late prof. M-Q Lu (left) of Nanjing University for his efforts and contributions. (e) a part of resulted networks showing well for groundwater, access tube for neutron moisture

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*3.2.1. Precipitation*

Recently, the average thickness of the soil is lower than that in 1982, especially in the upstream (**Figure 13**). To date, the average thickness of the soil in the upstream (~85 cm) has been less than that in the downstream (~105 cm) and that in the midstream (~103 cm).

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**Figure 10.** Construction of groundwater monitoring well. (a) the slotted part of steel tube; (b) the tube was wrapped up by plastic net; (c) making clay balls for using; (d) during installing, the space between the tube and drilling hole above the slotted lengths (shown by a yellow arrow) should be carefully stuffed up by small dried clay balls using a special designed tool. This picture is shown in commemoration of the late prof. M-Q Lu (left) of Nanjing University for his efforts and contributions. (e) a part of resulted networks showing well for groundwater, access tube for neutron moisture gauge and the tensiometer with connection plastic tubes to the scanner.

**Figure 11.** Construction of troughs. SR-trough for surface runoff; SSR30-trough for subsurface runoff at the depth of 30 cm below the ground surface; SSR60-that at the depth of 60 cm; SSR100-that at the depth of 100 cm.

#### **3.2. Instrumentation in Hydrohill catchment**

#### *3.2.1. Precipitation*

workers are happy to follow our lazy filling and the time-consuming checking on depths and bulk density of whole area by paying hourly wages. After whole area was completed, it was allowed to settle for 3 years before equipped (**Figure 9c**), while the natural grasses were revitalized. We then have opportunity to remeasure the established bulk densities during first exaction for the main

*works for both saturated and unsaturated zone.* Three networks including 22 wells for saturated water (groundwater) table measurements and groundwater sampling, 21 aluminum alloy access tubes for neutron moisture gauge were installed, all of them were drilled to the aquiclude (**Figure 9d**). The tubes for groundwater monitoring were slotted along the lowermost 20 cm and wrapped up by plastic net (**Figure 10a** and **b**). After installation into the drilling hole, the space around the slotted lengths were packed with sands to allow movement of groundwater to the well, however, the space above the slotted lengths should be carefully stuffed up by small dried clay balls to prevent any water other than groundwater intruding along the pipes (**Figure 10c** and **d**). Different from the tube for groundwater, the neutron access tubes should have an intact wall with sealed bottom, using threaded cap with a hanging pack of desiccant for sustaining a state of dryness in the tube (**Figure 6e**). A part of resulted networks is shown in **Figure 10d**. (5) *Drainage trenches.* After the installation of groundwater wells and access tubes, the drainage trenches including the main longitudinal trench and the side trench perpendicular to the main trench at the watershed outlet were dug up (**Figure 9e**). (6) *The layered troughs*. It was worked first from the bottom one. The splicing fiberglass troughs each 40 cm wide and some steel supports are shown in **Figure 9f**, **Figure 9g** shows the rectangular trough for SSR100 and steel supports for the setting of trough above it, that is, the SSR60. These troughs were constructed as shown in **Figure 11**, they were stacked on top of each other to create a set of long zero-tension lysimeters, each trough has a 20 cm aluminum lip that extends horizontally into the soil layer to prevent leakage between layers (**Figure 11**).(7) *The inverted filter*. There is a gap between the trough and the soil (**Figure 9h**) for the inverted filter (**Figure 11**) including the filling materials and the nylon net at the soil side and the stainless steel screen at the trough side (**Figure 9h** and **i**, **Figure 11**). (8) *The connection troughs*. With different curvatures, these troughs link the runoff troughs with the approaching part of measuring structures individually (**Figure 9j** and **k**). (9) *Discharge measuring structures.* We combined the V-notch sharp crested weir and the logarithm-notch sharp crested weir together, and defined it as the V-notch based logarithm sharp crested weir (**Figure 9l**) for discharge measurement of SR and SSRs. (10) At last, 30 hole sites for tensiometers at different depths together with the connection tubes from tensiometer to the scan-

After the finalization of construction, the artificial Hydrohill catchment has a drainage area of

vious version since 1982 (**Figure 12a–d**), and the renovation version (**Figure 12e**–**h**). The lengths of the longitudinal trough (5 in **Figure 12b**, **c**, **e**, **g**) and the transverse trough (4 in **Figure 12b** and **e**) are 29.4 and 6.8 m, respectively. The width of the trough is 0.4 m. The horizontal pro-

Recently, the average thickness of the soil is lower than that in 1982, especially in the upstream (**Figure 13**). To date, the average thickness of the soil in the upstream (~85 cm) has been less

than that in the downstream (~105 cm) and that in the midstream (~103 cm).

(inclined surface) as shown in **Figure 12** including its pre-

, and thus horizontal projected area of soil surface is 487.2 m<sup>2</sup>

.

of 50–75 cm, and 1.60 g/cm3

at the top soil of 0–30 cm, 1.42 g/cm3

of the layer at the

of 75–100 cm. (4) *Setting up monitoring net-*

trench later during 1981, it is 1.44 g/cm3

264 Hydrology of Artificial and Controlled Experiments

ning recorder were set up (**Figure 10e**).

jected area of the trough is 13.8 m<sup>2</sup>

(horizontal projection), 512 m<sup>2</sup>

490 m<sup>2</sup>

depth of 30–50 cm, 1.40 g/cm3

To monitor the distribution of rainfall and test the spatial uniformity of the rainfall generated by a rainfall simulator, 12 standard rain gauges (**Figure 14a** and **b**) and 5 tipping bucket

**Figure 12.** Finalization of the artificial catchment Hydrohill, its previous version (1982–1995) and renovation version (since 2012). (a) a satellite image showing Hydrohill and the whole hillslope area to be excavated of ca 4700 m<sup>2</sup> ; (b) and (c) the previous version of equipped Hydrohill; (d) the environment of Hydrohill. 1-land surface of Hydrohill; 2-an uncompleted artificial catchment; 3-the outlet of the Bloomhill Basin showing a discharge measuring structure of the gauging station; 4-the side trench perpendicular to the main trench at the watershed outlet; 5-the main longitudinal trench with layered troughs; 6-energy budget monitoring apparatus; 7-a scanning recorder for soil water potential from distributed sensors; 8-the neutron moisture gauge is in operation; 9-underground house for the discharge measuring structures; 10-laboratory for the calibration of neutron moisture gauge (1982–1988); 11-water supply tower; 12-two lysimeters with layered runoff troughs, 4 × 8 m<sup>2</sup> each, two different soils; 13-movable rainfall simulator at rest; 14-a reservoir for water supply of rainfall simulator; 15-a dual polarization Doppler precipitation radar for the areal precipitation monitoring of the Bloomhill Basin with drainage area of 80 km<sup>2</sup> ; 16-tracks for the moving of rainfall simulator; 17-laboratory for instrument measuring of isotopes; 18-various monitoring wells, sensors, samplers.

rain gauges (**Figure 14a** and **c**) were installed within the catchment. To test the measurement accuracy of the tipping bucket rain gauge, a 10-L plastic pot was connected with the drainage holes in the bottom of the tipping-bucket rain gauge (**Figure 14c**).

Runoff collected from trough SSR30 is the interflow from the unsaturated zone, but that from trough SSR60 will depend on the depth of the saturated zone due to the fluctuation of groundwater table. In case when the saturated zone table (plus its capillary fringe) is lower than the trough, then the runoff measured in SSR60 is the interflow from the unsaturated zone; otherwise, it will be the groundwater flow from the saturated zone. Water collected in troughs is routed by measuring structures as shown in **Figure 15** (the renovation version). For each weir, a pressure-type water level gauge (LEV1, ADCON) and a probe-type water level gauge (NKY08-2, NHRI) are adopted to simultaneously measure the water head above

**Figure 14.** Instrumentation for precipitation measurement in Hydrohill: (a) locations of 12 standard rain gauges and 5 tipping bucket rain gauges; (b) a standard rain gauge; (c) a tipping-bucket rain gauge. 1-external structure, 2-internal

structure, 3-a plastic pot used to collect total precipitation of each event.

**Figure 13.** Changes in the filling soil thickness of the Hydrohill catchment: (a) Isoline of catchment soil depth in 1982; (b)

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that in 2017; (c) hypsographic map of soil surface obtained from a three-dimensional laser scanner (2017).

the weir.

#### *3.2.2. Runoff components*

The uppermost trough (**Figures 11** and **15**) collects rain; the next lower trough collects surface runoff (SR); the three lower troughs collect subsurface flow from soil layers of the depths of 0–30, 30–60, and 60–100 cm (inferred as SSR30, SSR60, and SSR100 troughs). Practice on the Watershed Hydrological Experimental System Reconciling Deterministic… http://dx.doi.org/10.5772/intechopen.79357 267

**Figure 13.** Changes in the filling soil thickness of the Hydrohill catchment: (a) Isoline of catchment soil depth in 1982; (b) that in 2017; (c) hypsographic map of soil surface obtained from a three-dimensional laser scanner (2017).

**Figure 14.** Instrumentation for precipitation measurement in Hydrohill: (a) locations of 12 standard rain gauges and 5 tipping bucket rain gauges; (b) a standard rain gauge; (c) a tipping-bucket rain gauge. 1-external structure, 2-internal structure, 3-a plastic pot used to collect total precipitation of each event.

rain gauges (**Figure 14a** and **c**) were installed within the catchment. To test the measurement accuracy of the tipping bucket rain gauge, a 10-L plastic pot was connected with the drainage

14-a reservoir for water supply of rainfall simulator; 15-a dual polarization Doppler precipitation radar for the areal

simulator; 17-laboratory for instrument measuring of isotopes; 18-various monitoring wells, sensors, samplers.

each, two different soils; 13-movable rainfall simulator at rest;

; 16-tracks for the moving of rainfall

**Figure 12.** Finalization of the artificial catchment Hydrohill, its previous version (1982–1995) and renovation version (since 2012). (a) a satellite image showing Hydrohill and the whole hillslope area to be excavated of ca 4700 m<sup>2</sup>

(c) the previous version of equipped Hydrohill; (d) the environment of Hydrohill. 1-land surface of Hydrohill; 2-an uncompleted artificial catchment; 3-the outlet of the Bloomhill Basin showing a discharge measuring structure of the gauging station; 4-the side trench perpendicular to the main trench at the watershed outlet; 5-the main longitudinal trench with layered troughs; 6-energy budget monitoring apparatus; 7-a scanning recorder for soil water potential from distributed sensors; 8-the neutron moisture gauge is in operation; 9-underground house for the discharge measuring structures; 10-laboratory for the calibration of neutron moisture gauge (1982–1988); 11-water supply tower;

; (b) and

The uppermost trough (**Figures 11** and **15**) collects rain; the next lower trough collects surface runoff (SR); the three lower troughs collect subsurface flow from soil layers of the depths of 0–30, 30–60, and 60–100 cm (inferred as SSR30, SSR60, and SSR100 troughs).

holes in the bottom of the tipping-bucket rain gauge (**Figure 14c**).

precipitation monitoring of the Bloomhill Basin with drainage area of 80 km<sup>2</sup>

12-two lysimeters with layered runoff troughs, 4 × 8 m<sup>2</sup>

266 Hydrology of Artificial and Controlled Experiments

*3.2.2. Runoff components*

Runoff collected from trough SSR30 is the interflow from the unsaturated zone, but that from trough SSR60 will depend on the depth of the saturated zone due to the fluctuation of groundwater table. In case when the saturated zone table (plus its capillary fringe) is lower than the trough, then the runoff measured in SSR60 is the interflow from the unsaturated zone; otherwise, it will be the groundwater flow from the saturated zone. Water collected in troughs is routed by measuring structures as shown in **Figure 15** (the renovation version). For each weir, a pressure-type water level gauge (LEV1, ADCON) and a probe-type water level gauge (NKY08-2, NHRI) are adopted to simultaneously measure the water head above the weir.

*3.2.3. Soil moisture*

*3.2.4. Groundwater*

Germany, see **Figure 17c**).

*3.2.5. Evaporation from land surface*

unit outside the Hydrohill catchment.

*3.2.6. Movable rainfall simulator*

*3.2.7. Water sampling*

60, 70, 80, and 90 cm (**Figure 16c**).

A network of 21 aluminum alloy access tubes for neutron moisture gauges were constructed previously (1982–1995). Since then, all aluminum alloy access tubes have been displaced with 31 profile soil moisture sensors (PR2, Delta-T, UK), with their locations shown in **Figure 16a**. Each sensor has six sensor points located at the 10, 20, 30, 40, 60, and 100 cm (**Figure 16b**). Another six profiles with another kind of soil moisture sensors (SM-1, ADCON, Germany) were installed as well. This type of SM-1 has nine sensor points located at the 10, 20, 30, 40, 50,

Practice on the Watershed Hydrological Experimental System Reconciling Deterministic…

An array of 22 galvanized tube wells intersect through the soil till the concrete aquiclude (**Figure 17a**). Water table measurement is performed with level sensors (LEV1, ADCON,

An energy budget system (**Figure 18a**) and an eddy covariance system (**Figure 18b**) were mounted for accurate monitoring evaporation. The systems were equipped with the following

analyzer (Campbell, USA), three air temperature and moisture sensors (HMP155A, Vaisala, Finland), four-way net rasiometers (CNR4, Kipp and Zone, Netherlands), one ground surface infrared temperature sensor (SI-111, Campbell, USA), five soil temperature sensors (109, Campbell, USA), five soil moisture sensors (CS616, Campbell, USA), and four soil heat flux sensors (HFP01SC, Huksflux, USA). In addition, a small aperture scintillometer (SLS-40A, SCINTEC, Germany, see **Figure 18c**) is to be installed with its transmitter unit and receiver

A movable rainfall simulator system (**Figure 19a**) was designed and constructed over the Hydrohill catchment in 2012. This system consists of five sub-systems, which can be controlled independently by the control platform (**Figure 19d**) to generate different rainfall intensities (10–200 mm/h) via the combination of different sizes of sprinkle nozzles (**Figure 19e**) with regulations of water pressure. **Figure 20** shows the schematic diagram of the rainfall simula-

the Hydrohill catchment (**Figure 19b**), and the spatial uniformity of the simulated rainfall is larger than 0.8. After the simulating rainfall event is finished, the rainfall simulator system can

Water samples from precipitation, runoffs, soil, groundwater, and plants were collected.

/H<sup>2</sup>

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, which can effectively cover

O infrared gas

sensors: one 3-D ultrasonic anemometer (C150, Campbell, USA), one CO<sup>2</sup>

tor system. The rainfall area of this modeling system is 656 m<sup>2</sup>

be moved to the outside of Hydrohill catchment (**Figure 19c**).

Analysis indexes for water samples are included in three categories:

*3.2.7.1. Water sample types and analysis indexes*

**Figure 15.** The discharge measuring structures of renovation version and the instrumentation for its water heads. 1-probe-type water level gauge; 2-tracking gauge for the real-time water head process.

**Figure 16.** Instrumentation for soil water measurement in Hydrohill catchment: (a) the locations of the soil moisture sensors and soil water sampling points; (b) the UK soil moisture sensor (PR2, Delta-T, UK); (c) the German soil moisture sensor (SM-1, ADCON, Germany).

#### *3.2.3. Soil moisture*

A network of 21 aluminum alloy access tubes for neutron moisture gauges were constructed previously (1982–1995). Since then, all aluminum alloy access tubes have been displaced with 31 profile soil moisture sensors (PR2, Delta-T, UK), with their locations shown in **Figure 16a**. Each sensor has six sensor points located at the 10, 20, 30, 40, 60, and 100 cm (**Figure 16b**). Another six profiles with another kind of soil moisture sensors (SM-1, ADCON, Germany) were installed as well. This type of SM-1 has nine sensor points located at the 10, 20, 30, 40, 50, 60, 70, 80, and 90 cm (**Figure 16c**).

#### *3.2.4. Groundwater*

**Figure 15.** The discharge measuring structures of renovation version and the instrumentation for its water heads.

**Figure 16.** Instrumentation for soil water measurement in Hydrohill catchment: (a) the locations of the soil moisture sensors and soil water sampling points; (b) the UK soil moisture sensor (PR2, Delta-T, UK); (c) the German soil moisture

sensor (SM-1, ADCON, Germany).

1-probe-type water level gauge; 2-tracking gauge for the real-time water head process.

268 Hydrology of Artificial and Controlled Experiments

An array of 22 galvanized tube wells intersect through the soil till the concrete aquiclude (**Figure 17a**). Water table measurement is performed with level sensors (LEV1, ADCON, Germany, see **Figure 17c**).

#### *3.2.5. Evaporation from land surface*

An energy budget system (**Figure 18a**) and an eddy covariance system (**Figure 18b**) were mounted for accurate monitoring evaporation. The systems were equipped with the following sensors: one 3-D ultrasonic anemometer (C150, Campbell, USA), one CO<sup>2</sup> /H<sup>2</sup> O infrared gas analyzer (Campbell, USA), three air temperature and moisture sensors (HMP155A, Vaisala, Finland), four-way net rasiometers (CNR4, Kipp and Zone, Netherlands), one ground surface infrared temperature sensor (SI-111, Campbell, USA), five soil temperature sensors (109, Campbell, USA), five soil moisture sensors (CS616, Campbell, USA), and four soil heat flux sensors (HFP01SC, Huksflux, USA). In addition, a small aperture scintillometer (SLS-40A, SCINTEC, Germany, see **Figure 18c**) is to be installed with its transmitter unit and receiver unit outside the Hydrohill catchment.

#### *3.2.6. Movable rainfall simulator*

A movable rainfall simulator system (**Figure 19a**) was designed and constructed over the Hydrohill catchment in 2012. This system consists of five sub-systems, which can be controlled independently by the control platform (**Figure 19d**) to generate different rainfall intensities (10–200 mm/h) via the combination of different sizes of sprinkle nozzles (**Figure 19e**) with regulations of water pressure. **Figure 20** shows the schematic diagram of the rainfall simulator system. The rainfall area of this modeling system is 656 m<sup>2</sup> , which can effectively cover the Hydrohill catchment (**Figure 19b**), and the spatial uniformity of the simulated rainfall is larger than 0.8. After the simulating rainfall event is finished, the rainfall simulator system can be moved to the outside of Hydrohill catchment (**Figure 19c**).

#### *3.2.7. Water sampling*

#### *3.2.7.1. Water sample types and analysis indexes*

Water samples from precipitation, runoffs, soil, groundwater, and plants were collected. Analysis indexes for water samples are included in three categories:

① General parameters: electrical conductivity (EC), pH, dissolved oxygen (DO), and water temperature;


**Figure 17.** Instrumentation for groundwater measurement in Hydrohill catchment: (a) locations of the monitoring wells; (b) the monitoring well (1-the galvanized tube, 2-the connection cable of the level sensor, 3-a plastic tube for sampling groundwater); (c) the level sensor which is a pressure transducer with atmospheric pressure compensation; (d) a remote terminal unit (RTU) receive the data from the groundwater level sensors (LEV1, ADCON, Germany) and send the obtained data to the gateway via radio together with that from soil moisture sensor as shown in **Figure 16** (SM-1, ADCON, Germany).

*3.2.7.2. Sampling for precipitation*

**Figure 20.** Schematic diagram of the rainfall simulator system.

sizes of sprinkle nozzles.

*3.2.7.3. Sampling for runoff components*

Rain water samples were collected using two methods: first is via the rainfall trough, which

**Figure 19.** Rainfall simulator system in Hydrohill: (a) before the rainfall simulating; (b) during the rain simulating; (c) after the rainfall simulating event (1-an impounding reservoir supplying the rainfall simulator system, 2-a water supplying pipe); (d) the rainfall simulator control platform located in the gauging room; (e) combination of different

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second is via a specially designed rain gauge with a diameter of 40 cm, which was installed on the roof of the gauging room (**Figure 21b**). The result from these two methods shows that

To easily and to fast collect water samples of different runoff components in Hydrohill, a batch sampling system is designed and constructed based on negative pressure (**Figure 23**). The schematic of the batch sampling system is shown in **Figure 23a**. Water samples for runoff components are collected via a stainless steel tube head fixed at the connection trough before

(**Figure 21a**), the

serves as a rain gauge distributed longitudinally with total area of 13.8 m<sup>2</sup>

they are similar to each other with only few exceptions (**Figure 22**).

the runoff reaches the ponding of the weir (**Figure 23c**).

**Figure 18.** Instrumentation for the evaporation from ground surface in Hydrohill. (a) An energy budget system; (b) an eddy covariance system; (c) a small aperture scintillometer.

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**Figure 19.** Rainfall simulator system in Hydrohill: (a) before the rainfall simulating; (b) during the rain simulating; (c) after the rainfall simulating event (1-an impounding reservoir supplying the rainfall simulator system, 2-a water supplying pipe); (d) the rainfall simulator control platform located in the gauging room; (e) combination of different sizes of sprinkle nozzles.

**Figure 20.** Schematic diagram of the rainfall simulator system.

#### *3.2.7.2. Sampling for precipitation*

**Figure 17.** Instrumentation for groundwater measurement in Hydrohill catchment: (a) locations of the monitoring wells; (b) the monitoring well (1-the galvanized tube, 2-the connection cable of the level sensor, 3-a plastic tube for sampling groundwater); (c) the level sensor which is a pressure transducer with atmospheric pressure compensation; (d) a remote terminal unit (RTU) receive the data from the groundwater level sensors (LEV1, ADCON, Germany) and send the obtained data to the gateway via radio together with that from soil moisture sensor as shown in **Figure 16** (SM-1, ADCON, Germany).

① General parameters: electrical conductivity (EC), pH, dissolved oxygen (DO), and water

− , CO3

2−, Cl−

, NO3 − , SO4

2−, and SiO<sup>2</sup>

;

temperature;

② Hydrochemistry: K<sup>+</sup>

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③ Isotopes: 18O, <sup>2</sup>

, Na<sup>+</sup>

H, and 15N.

, Ca2+, Mg2+, HCO3

**Figure 18.** Instrumentation for the evaporation from ground surface in Hydrohill. (a) An energy budget system; (b) an

eddy covariance system; (c) a small aperture scintillometer.

Rain water samples were collected using two methods: first is via the rainfall trough, which serves as a rain gauge distributed longitudinally with total area of 13.8 m<sup>2</sup> (**Figure 21a**), the second is via a specially designed rain gauge with a diameter of 40 cm, which was installed on the roof of the gauging room (**Figure 21b**). The result from these two methods shows that they are similar to each other with only few exceptions (**Figure 22**).

#### *3.2.7.3. Sampling for runoff components*

To easily and to fast collect water samples of different runoff components in Hydrohill, a batch sampling system is designed and constructed based on negative pressure (**Figure 23**). The schematic of the batch sampling system is shown in **Figure 23a**. Water samples for runoff components are collected via a stainless steel tube head fixed at the connection trough before the runoff reaches the ponding of the weir (**Figure 23c**).

**Figure 21.** Two methods for rainfall sampling: (a) method-1 using the rainfall trough as a longitudinal rain gauge; (b) method-2 using a specially designed rain gauge.

**Figure 23.** Instrumentation for sampling runoff components in Hydrohill: (a) the schematic of the batch sampling system; 1-the negative-pressure extender, 2-three-way valve, 3-sample bottles, 4-a stainless steel tube head enclosed by a yarn to stop sand and litter into the sampling tube, 5-troughs, 6-a safeguard bottle, 7-a vacuum pump, 8-a container used to drain the old water in the tubes, 9-a valve to drain the water in the container; (b) photo of a batch sampling system based on negative pressure; (c) a stainless steel tube head fixed at the connection trough before the runoff reaches the

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**Figure 24.** Instrumentation for sampling soil water and groundwater in Hydrohill: (a) locations of the sampling points of the soil water and groundwater; (b) schematic of a batch sampling system designed and constructed based on negative pressure for sampling soil water; (c) that for sampling groundwater; (d) a suction lysimeter; (e) photo of a batch sampling system designed and constructed based on negative pressure for sampling soil water and also for groundwater; (f) the tube previously fixed on the level sensor to sample groundwater. 1-sample bottles, 2-tubes connecting with suction

lysimeters or groundwater wells, 3-the negative-pressure extender.

ponding of the weir.

**Figure 22.** Comparison of results from two methods for rainfall sampling. Method-1: Using the rainfall trough; Method-2: Using a specially designed rain gauge. Data is resulted from a rainfall event in 2016.

#### *3.2.7.4. Sampling for soil water and groundwater*

To sample the soil water, 31 suction lysimeters (**Figure 24a** and **d**) were installed at three depths: 9 at 15 cm, 12 at 45 cm, and 10 at 80 cm. To keep the synchronism of sampling, a batch sampling system is designed and constructed based on negative pressure (**Figure 24b** and **e**). Groundwater samples of 22 points were collected with the tubes previously fixed on the level sensors (**Figure 24a** and **f**). Similarly, a batch sampling system is designed and constructed based on negative pressure to keep the synchronism of sampling groundwater (**Figure 24c** and **d**).

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**Figure 23.** Instrumentation for sampling runoff components in Hydrohill: (a) the schematic of the batch sampling system; 1-the negative-pressure extender, 2-three-way valve, 3-sample bottles, 4-a stainless steel tube head enclosed by a yarn to stop sand and litter into the sampling tube, 5-troughs, 6-a safeguard bottle, 7-a vacuum pump, 8-a container used to drain the old water in the tubes, 9-a valve to drain the water in the container; (b) photo of a batch sampling system based on negative pressure; (c) a stainless steel tube head fixed at the connection trough before the runoff reaches the ponding of the weir.

**Figure 21.** Two methods for rainfall sampling: (a) method-1 using the rainfall trough as a longitudinal rain gauge; (b)

**Figure 22.** Comparison of results from two methods for rainfall sampling. Method-1: Using the rainfall trough; Method-2:

To sample the soil water, 31 suction lysimeters (**Figure 24a** and **d**) were installed at three depths: 9 at 15 cm, 12 at 45 cm, and 10 at 80 cm. To keep the synchronism of sampling, a batch sampling system is designed and constructed based on negative pressure (**Figure 24b** and **e**). Groundwater samples of 22 points were collected with the tubes previously fixed on the level sensors (**Figure 24a** and **f**). Similarly, a batch sampling system is designed and constructed based on negative pressure to keep the synchronism of sampling groundwater (**Figure 24c** and **d**).

Using a specially designed rain gauge. Data is resulted from a rainfall event in 2016.

*3.2.7.4. Sampling for soil water and groundwater*

method-2 using a specially designed rain gauge.

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**Figure 24.** Instrumentation for sampling soil water and groundwater in Hydrohill: (a) locations of the sampling points of the soil water and groundwater; (b) schematic of a batch sampling system designed and constructed based on negative pressure for sampling soil water; (c) that for sampling groundwater; (d) a suction lysimeter; (e) photo of a batch sampling system designed and constructed based on negative pressure for sampling soil water and also for groundwater; (f) the tube previously fixed on the level sensor to sample groundwater. 1-sample bottles, 2-tubes connecting with suction lysimeters or groundwater wells, 3-the negative-pressure extender.

#### **3.3. Analyses of water samples**

#### *3.3.1. General parameters*

Electrical conductivity (EC) was measured in the field using a portable EC digital analyzer (HQ14d, Hach, USA). Dissolved oxygen (DO), pH, and water temperature were measured in the field using a multi-parameter digital analyzer (HQ40d, Hach, USA). These parameters were determined immediately after water samples had been collected.

#### *3.3.2. Hydrochemistry*

Most chemical analyses were undertaken at the Tiexinqiao experiment base of Nanjing Hydraulic Research Institute, China. All water samples were analyzed within 2 weeks of the date of collection. Concentrations of the major cations (Na+ , K<sup>+</sup> , Ca2+, and Mg2+) were analyzed by inductively coupled plasma optical emission spectrometry (ICP-OEC, see **Figure 25a**), and the anions (SO4 2−, Cl− , NO3 − , and F− ) were analyzed by DIONEX ICS-2100 ion chromatography (**Figure 25b**). All samples were filtered through a 0.45 μm filter before laboratory analysis. The analytical precision of the measurement of ions was determined by calculating the absolute error in ionic balance, and the analytical error was less than ±2% for the anions and between ±1.5 and ±4% for the cations. HCO3 − concentrations were determined by a titration assay on site or within 24 h of sample collection.

#### *3.3.3. Isotopes*

Soil and plant waters were previously obtained via a vacuum extraction system (LI-2000, LICA, China, **Figure 26a**). The δ18O and δD of water samples determined using a liquid water isotope analyzer (908-0008, LGR, USA, **Figure 26b**) or a liquid–gas water isotope analyzer (L2120–i, Picarro, USA, **Figure 26c**). The dual isotopes of nitrate were prepared by quantitative bacterial reduction of nitrate to nitrous oxide (N2 O) using the denitrifier method followed by automated extraction and purification using Trace Gas Pre-concentrator unit (IsoPrime Ltd., Cheadle Hulme, Cheadle, UK) and analysis of the N<sup>2</sup> O product using an isotope ratio mass spectrometer (GV, IsoPrime, **Figure 26d**). Four international nitrate (USGS-32, USGS-34, USGS-35, and IAEA-N3) and experimental reference materials that were treated identically with the water samples were used to calibrate the measured sample data. Each sample was measured in duplicate and the standard error was 0.3‰ for δ15N-NO3 − and 0.5‰ for δ18O-NO3 − .

**4. Some results**

Picarro, USA); (d) IsoPrime100.

**4.1. Explore the possible paths**

**4.2. Explore the subsurface runoff components**

surface and subsurface runoff components ([1, 7]).

Aimed at ending the scientific stalemate on our watershed experimental studies. Since 1982, the origin of CHL, from classic natural experimental watershed, current pedon lysimeter, and the uncompleted experimental system until the Chuzhou WHES, various possible paths are tried for the emerging of some possible paths ([1–6]), to achieve hopefully the sustainable development of the watershed hydrological experimentation. It is found that the intermediate "mesos" including those of controlled-nature and artificial-nature with constrain and add complexity respectively, show its crucial importance for revealing the individual mechanisms hidden deep. Philosophically, it is "the golden mean between two extremes of character" in Book IV of his Ethics of Aristotle, and the idea of "holding the two extremes and using the

**Figure 26.** Instruments adopted in isotope analysis of water samples: (a) a vacuum extraction system (LI-2000, LICA, China); (b) a liquid water isotope analyzer (908–0008, LGR, USA); (c) a liquid–gas water isotope analyzer (L2120–i,

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middle impartial" in China for the "music" of our watershed experimental studies.

• Direct measurement: After progressively improving, the method of longitudinal zerotension lysimeter (layered trough) is used in catchment scale for the direct measurement of

**Figure 25.** Instruments adopted in hydrochemistry analysis of water samples: (a) inductively coupled plasma optical emission spectrometry (ICP-OEC); (b) ion chromatography (ICS-2100, DIONEX, USA).

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**Figure 26.** Instruments adopted in isotope analysis of water samples: (a) a vacuum extraction system (LI-2000, LICA, China); (b) a liquid water isotope analyzer (908–0008, LGR, USA); (c) a liquid–gas water isotope analyzer (L2120–i, Picarro, USA); (d) IsoPrime100.
