Research Of Shaded Green Space Landscape Based On Natural Light Environment Under The Urban Viaducts

Urban viaducts are used for solving serious traffic problems in modern cities, but they have brought negative impacts on urban environment, economy and landscape, which produce some passive spaces under viaducts. The green space is one of effective ways to solve this problem, but the green plants can't grow healthy because of the inadequate lighting, lack of rainwater, traffic pollution and other issues under viaducts.This paper used the Ecotect Analysis software (Inc. UK) to analyze the daylight environment rules under viaducts. It tested the plants photosynthetic characteristic under viaducts, and then discussed the actively strategies of shaded green space landscape. The results indicated that:(1) There are 3 factors of the viaducts' construction, such as the viaducts' tending towards, the ratio of width and tallness of the space under viaduct (that is B value) and the separated slot width of viaducts, have great impact on the natural light environment under viaducts, and their orderliness were as followed.The average photosynthetic actively radiation (PAR) and the average sunshine hours in the spaces under the fine tending towards viaducts are much higher than the disbennifit viaducts, but the higher PAR(PAR≥3MJ/m2·d) area ratio and the high sunshine hours(sunshine hours≥50% full sunshine hours) area ratio under the fine are worse than the disbennifit ones. The PAR and the sunshine hours are linearity increasing in different ratio with the B argument under viaduct. It finds the critical B values by regression analysis that is, the critical value of B for decreasing the low PAR (<1 MJ/m2·d)area ratio: 0.367 for the fine tending towards viaducts,0.497 for the disbennifit tending towards viaducts. The critical value of B for decreasing the low sunshine hours (<1 MJ/m2·d) area ratio:0.43 for the fine tending towards viaducts,1.68 for the disbennifit tending towards viaducts. The lower PAR area disappeared when the viaduct separation width up to 2m, and the B value is 0.231; the lower sunshine hours area ratio close to 0 when the separation width up to 4m.(2) This paper divideed the shaded sorts of plants under viaducts in Wuhan city into 6 small types and 3 big types based on their light saturation points (LSP) and light compensation points (LCP).This paper tested 29 species of plants' Photosynthetic rates-photosynthetic photo flux density (Pn-PPFD) under viaducts in Wuhan city with LI-6400XT photosynthesis system (Inc. USA), figured out the plants'LSP and the LCP, and clustering these photosynthetic characteristics into 6 small types and 3 big types. This paper put forward 98 species of plants to adapt to the shade spaces under viaduct in Wuhan based on research and literatures, and it can provide references to enrich the plant species under Wuhan viaducts.(3) There are some rules for planting in adaptive survival areas on natural light environment under viaducts:The equal PAR lines parallel with the viaduct edges when the B value exceeds 0.3, and the best tolerant shaded plants,Ⅰ-A type plants can be planted 40 % width under the fine tending towards viaducts, theⅠ-B,Ⅱ-A,Ⅱ-B types 42%, a part ofⅢtype at 18% width of viaducts. However, the equal PAR lines distributing under the disbennifit tending towards viaducts are not uniformity, the ratio of width forⅠ-A is 60%, and other types are less than the fine viaducts.TheⅡ,Ⅲtype plants are also affected by sunshine hours, as a result, theⅠ,Ⅱtypes planting area are increasing and theⅢtype planting area is decreasing or disappearing under the two typical different tending toward viaducts. Calculated the two factors of natural light environment integration effect, we found the planting direct plan adapt to natural light environment under urban viaducts.(4) Non-adaptive survival areas have inverse proportion relationship with the B value under viaducts. This paper made suggestions such as pavement, prettification establishment, activity grounds to deal with this area, in particular, it proposed that we can construct a system of collecting, decontaminating the viaduct surface rainwater, and irrigating the shade plants, which maybe bring into play the landscape best benefit.Finally, this paper expected 3 issues which yet not be penetrated into and it expected be attention by craft brothers:1) be cautious of building viaducts, and treat the existent viaducts in reason, and we should exert the active use of the shade spaces under viaducts. Spaces under suburb viaducts may be used the urban agriculture places with green space on both sides,3) it may consider the sunshine reflecting boards technique on viaducts, the system of collecting, decontaminating the viaduct surface rainwater, and irrigating the shade plants.