**1. Introduction**

A framework of watershed hydrological experimental system (WHES) is suggested raised from the theoretical study on the complex hydrological system. It is defined as an experimental system to dialog with the complex watershed hydrological nature, to drive the opening of various doors of their black boxes aimed at revealing mechanisms hidden deep in the system with some degree of organization. In fact, the organization of the WHES is trying to reconciling the deterministic and stochastic extremes for the watershed hydrological complex system, "opposites are complementary" as the basic Chinese philosophy have revealed.

As a trial of the suggested WHES, the Chuzhou WHES is ongoing for tests. The constituent parts of the WHES can be resolved into four categories as the "macros", "mesos", "micros," and the "nucleus". "Macros" are composed by pure natural EBs at high level of complexity and randomness; "micros" by pure artificial chain at low level; they are two extreme levels in WHES, while the "mesos" are the chain of intermediate phase; actually, it will play the critical role, the "golden mean," in WHES as described in Chapter 11. The "nucleus" are water isotopes and solute isotopes from all chains of macros, mesos, and micros by overall sampling; it characterizes the internal linkages between them, and reveals their interrelated processes; actually, it is an essential condition of in WHES.

and clay loams; saprolite with prismatic and block structures, horizontal and vertical fissures and cracks developed in the upper regolith. The altitude difference of watershed approaches

**Figure 1.** (a) Hypsographic map of the ground surface of Nandadish; (b) hypsographic map of the bedrock surface; and

Practice on the Watershed Hydrological Experimental System Reconciling Deterministic…

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Aimed at a CZ hydrological experimental block aforementioned, the main construction tasks as sketchily shown in **Figure 2a** are threefold: (1) To change its original trench into the layered

**Figure 2.** (a) Schematic diagram of Nandadish showing the locations of main construction tasks; (b) original view of the main troughs and the catchment coverages during 1980; 1-trough for rainfall, which is served for separation of "channel rainfall" from surface runoff collected from trough 2, 2-for surface runoff (SR); (c) original view of the branch troughs with a watching gallery for the students practice to seeing the real processes of different runoff components during rainfall event; 1-trough for rainfall, 2-for surface runoff (SR), 3, 4-for subsurface runoff (SSR) from troughs at different depths; (d) measuring structures under construction for different troughs, 1-for rainfall (V-notch sharp crested weir), 2-for SR (V weir and rectangular sharp crested weir), 3-for SSR (V weir and rectangular weir), 4-for SSR (V weir), 5-for total runoff (V weir and rectangular weir, not shown); (e) a part of the underground "block divider" with 0.3 m above the ground surface; (f) the change of runoff compositions within time span of 20 years compared with July 1989 and July

12.9 m with a surface slope ranging from 6.7 to 17.1%.

2009 using same measuring structures with different catchment coverages.

(c) Isopachous map of the deposit thickness (including surficial soil).

In Chuzhou WHES, there are two extremes in the intermediate "meso" blocks (Figure 8a in Chapter 11): One is the controlled-natural Nandadish based on the strategy of constrain complexity, another one is the artificial-natural Hydrohill on that of add complexity. Nandadish is designed to meet with the idea on Critical Zone Experimental Block with an intention trying to replace the current Experimental basins suggested by the Representative and Experimental Basin Programme of the first International Hydrology Decade (IHD) since 1965. These two typical experimental meso-mediation blocks of Chuzhou WHES are reviewed here.
