Study On Dynamics Of Gully Erosion And Its Controlling In The Black Soil Region, Northeast China

The black soil region of northeast China is an important food production area, as well as a serious soil erosion area in China. This research aimed to discover the reason of gully developing fast in resent 20 years than ever before, through investigate gullies'distributing and analyze its modality. Provide with reference for soil and water conservation in the black soil region in northeast China. Through research on 77 gulies in 5 watersheds that located in different climate region, and contrast Sanchahe watershed's map (1986) with the watershes's satellitic photo (2007), we found that the gully developing rate was very difference even the slope land conformed both in gradient and surface roughness. The research result show as follows:1. Gullies mainly take place on sloping farmland: through investigate 5 watersheds which located in different landforms, agrotypes and soil erosion zones, we foud that there are total 77 gulies in the 5 watersheds, 66 of the gullies take place in sloping farmland, account for 85.71%; 5 of the gullies take place in wasteland;. 3 of the gullie take place by roads; 2 of the gullies take place in open forest land; 1 of the gullies takes place in farmland.2. Gullies'modality in sloping farmland shows that the motivity of drive gully developing is largely from gully's two sides: the modality shows that the gullies in sloping farmland, its WLR and WDR are big than others. That indicate run off from sloping farmland and inflood gully through its two sides are quite abundance. Consequentially, the gullies in sloping farmland are broadening.3. Furrow s between ridges in a field perform an important function of accordant junction: Furrow s'cross section is triangle, precipitation were gathered in Furrow s. Precipitation can produce runoff in Furrow s after subtract loss from evaporation, interception by crop or plant, infiltration. After runoff gathered by Furrow s, the runoff depth can be many times higher than it in flat ground.4. Effect of aqueduct is the main reson for gully developing quickly: because farmer changed sloping ridge into contour ridging, it makes accordant junction condition changed in sloping farmland. Each of furrows like a small ditchs or small aqueduct canals that caused runoff flow along furrow orientation and break out in low-lying and weak site of ridge. Runoff overfall can gather into stream flow and scour out gullies. We define this process as Effect of aqueduct. Because the reson of Effect of aqueduct, the gullies in sloping farmland were developing quickly.5. Effect of accordant junction play a significant role for give birth to gully and its developing: the result of research in Sanchahe watershed show that runoff occur in contour ridged furrow in a field of sloping farmland, the quantity of runoff gathered into stream flow can be 80～1700 times than the quantity caused in a single sloping furrow. Gathered stream flow can washed out sloping farmland and cause gully erosion.6. Changing sloping ridge into contour ridge early, the gully developing be at a high pitch: the resoult of research on 5 watersheds show that the gully developing quickly in the sloping farmland where changed the sloping ridge into contour ridge early, no matter in length and erosion quantity both at first level.7. High strength precipitation in summer promoted the effect of aqueduct: the average annully high strength precipitation probability which produced runoff run over the capacity of furrow in research watersheds is 14%. That means thare are high strength precipitation should occur in 7 years that the furrow unable to contain. In this case, overflow furrow is inevitably for the precipitation quantity exceeds the capacity of furrow.8. Most the ridge lengths in the black soil region are exceed the critical length of ridge: in the condition that furrow's gradient is uniformily, runoff produced in a definite lenth of furrow can cause ridges break up in lower and weak site; the definite lenth is the critical length of ridge. According to the resoult of research in Sanchahe watershed, if the precipitation intensity reaches 32mm/h, the critical length of ridge should be 138.91m. The ridges lenth in the black soil region usually more than 500m, which exceed the critical length of ridge under the characteristic precipitation in the region. So that easy to cause gully erosion.9. Control gully erosion should take multiform combined-measures and used them according to gully size magnitude: through comprehensive investigation, 6 modes which used for control different kind of gullies and control gullies at different size magnitude were given in this paper. Such as control ephemeral gully, small size gully, middle size gully and big size gully. Then we discussed those modes'effect both in conservation and economic benefit.