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A-weighted sound levels between 78 to 89 dB were observed immediately above the dropping point of nappe on the water surface in the stilling basin of drop structures of the Togashi main canal of the Shichika Irrigation District, Ishikawa, Japan. According to the noise distribution survey conducted at the noisiest drop structure of 89 dB, A-weighted sound pressure levels between 62 to 67 dB which exceeded the Japan's environmental quality standard were observed in the cross-section adjacent to ordinary houses located 25 m downstream of the drop. Therefore, the noise reduction experiments of gabion mattress, using the 1/8 scale-downed hydraulic model of the drop structure of water-cushion type, were conducted. The experiments showed significant reduction of sound levels in the cases of trapezoid-shaped and inverted trapezoid-shaped gabion mattress with single or double-slit. Then, the flow velocity measurement showed that the sound levels above the dropping point of nappe were positively correlated with the mean flow velocities in the stilling basin. Keywords: A-weighted sound level; Gabion mattress; Water-cushion-type drops; Hydraulic model; Shichika Irrigation District 1 +&0CD KnN +ÞvJ 0 I On1 +oË6S c#LK0Ú [wGOn1+oï 4 !0CD)êK3⁄4|vJ7ï<Î PQ# w0Qâ " èé+r4 ̈GLG`S ̈SÐ?01970&ì "¥ |0Ú PQ,±ä60 °B 7Ó )+IJS ̈ 7c RP R ;1982<!0Á ö#)iu¿ K[` Sjk(vG)ê4\PQ2f*+  ̈ a#0ï<Î =æ) ¿ PQ pSGüK SÝ|¥K67Â¥0 iu#u4PQ  ̈vK S óD,AV a#+4 ̈G¥`7a#0 Q K[ Ù§+ï<Î4! ©j4 a#,4567c =;1990<!04j ¥| ï=æ pQÙ§#6SæJ, 9 Töd4äV #Ó0=æ¥| ?æ©vI KA kPQÎU{+p *67a#0ï=æJ PQ!sõZN7?ï= {V #RX6S a#,4567cs70|;1996<\0 ́ KÐV å3⁄4 )z Î/muï<ÎKÐ S0Qâè 3 ÎU{ PQÎU{;A k<#sõZN? ï= {V {V WX* RX, 67Â¥0)z Î/muï<ÎKÐV æ)Q )êò) "æ) QRpS!=æ) Kj610}15S  ̈ a#G ü,4567c CD)ê&4\ï)Q Ù§K S )+ IJS cK3⁄4|vJ  ́Y KÐ S!0-æ)Z ÉßK[ ök9}ÉßKÙ6SE Fy,3⁄4|B a#+IJS c[·;1999<!0) iu¿  ́Á ¿ A¥|EFy3⁄4| K.), 6S cs70ø }3⁄4KÐ S\ï)QKÙB P QÙ§ 7ÓK=æ)  ̈K\ ,wpQÙ§+45 vJS ;}t¤02001<c R |;2006<!0(hi)ê öï< K S0 2fPQ,)ZÉß0ï=«4 2fQ0)Zôd ^ _) æ=QGü+RXB #K.0ï=3K]  ̈£ z,3⁄4|B a#+m 4 a#,456S ca [ wK0CD)ê ï<Î42fB PQK S!0 aJs4 )¥|0Ú 2f KÏV. + ÝvJ  +0fßGPQöpÙ§K S )!s o¦#! .G 9:K c L )!0;i<2þå9 æç3KÔ+ è) @ )ê4 ·^)KÐ SPQ¿ ö,  0ï<ÎKÐV PQÙ§ ¬Ñk,úûB a#0 ;ii<·^)K3⁄4|vJS )z Î/muï<ÎKÙ 6S0[? J7PQöp A,2_B \ m` 9 ,)iu¿ KÐ SabB a#0;iii<)iu¿ KÐ S0)z Î/m3 æ4¦ø,iVîæ4%K [`S%ä60ï<Î PQÎU{#æ4¦ø RX, Ý|¥KB a#,T#67c 1 ./01 éêÉëåEmeritus Professor, Ishikawa Prefectural University, 1-308 Suematsu, Nonoichi, Ishikawa 921-8836, Japan 2 ./01 äèRS àkIáâãJ äåEx-Student, Graduate School of Bioresources and Environmental Sciences, Ishikawa Prefectural University, 1-308 Suematsu, Nonoichi, Ishikawa 921-8836, Japan ./01 äèRS ìÉëåAssociate Professor, Faculty of Bioresources and Environmental Sciences, Ishikawa Prefectural University, 1-308 Suematsu, Nonoichi, Ishikawa 921-8836, Japan (Corresponding Author) E-mail:ichion@ishikawa-pu.ac.jp# ./01 äèRS ¶ÉåAssistant Professor, Faculty of Bioresources and Environmental Sciences, Ishikawa Prefectural University, 1-308 Suematsu, Nonoichi, Ishikawa 921-8836, Japan# 5 ?@ äèRSk ÉëåProfessor, Faculty of Life and Environmental Science, Shimane University, 1060 Nishikawatsu, Matsue, Shimane 690-8504, Japan# Journal of Rainwater Catchment Systems Vol.19/No.1/pp.37-43 Journal of Rainwater Catchment Systems JOURNAL OF RAINWATER CATCHMENT SYSTEMS/VOL.19 NO.1 2013 ▇ 37 2 TUNV 4 4 2.1 L4 L )4!0  2þå9 æç35,000ha, äc #B è),ÙS#67cè)!·^0d0 r0_÷0 R×0÷0æø è ) fE 4 cPQ¿ ö4!07 )ê 4\nN# eQR+U ·^) nNeÏ',ÙS)ê# 67;A 1<cÙS)ê 1U!4km40)z Î/mu ï<Î+32ò3⁄4|vJS cÚ ï<!00.40} 1.20m; e0.59m<40aJ| ï<Î¥|26ò ï< Î,;ï4PQ¿ ö,¿}67c 2.2 W*564 PQäÖK! 2mê fbPQ%;NL06<,ù6 7cPQ¿ ö!0ï<Îï=3ö=æ PQ ö# PQ¦ø ö 2 ö,¿}67cï=3ö=æ PQ ö!0)6  ̈+¥¥|G [wK0ï=3¥| 1.00m=æ0)d¥|0.50m") õ|4`7cäÖ!0 1g'S430ò A kQÕ,þ?»0 {V e ; dPQÎU{<,ÒÓ7caJ,3>h?i60Ú e ,PQÎU{#6S 67c PQ¦ø ö!0$\  ̈GPQÎU{, 67ï< Î,ÙS#6S`7c|;1996<,×KK6S0PQ QRpS+jk(v =æ) PQ¦ø, ö6 7cï<Î¥|=æ30=æ ò) Ð[qv) KÙ6S\PQ ¦ø ö,`7c+ò) ä«! ï<Î ï=3¥|=æ¿05m010m015m020m025m 5mþ»4)d¥|1.5m «0ò) ä«!)ê ¥|1m03m05m07m09m 2mþ»40v! "¥| 1.5m#3.5m#67caJ| v!0ÔÓ 1*#2*,^ Ö67\ 4 ;A 2<c 2.3 W*#$4 ï<Îö=æ4äÖvJ7PQÎU{!082}89dB; e84.3dB<4 `7c$\  ̈GPQ+2f6S 7 ! ï<ÎNo.29;A 3<4 `7c L ö!0·^) nNeÏ',ÙS#6S c öÏ'ô!0^_Y;2013< A ;j|nk  KovJ <Ð[qB ;È#6Snk KovJ <K¦,vJ +b c^_Y;2013<K[JT0 AÐ[qBÏ ^_$%!>'55dB&=0l'45dB &=4 ?0ï<Îö=æ4äÖvJ7PQÎU{!> '0l' $%,"> 4 `7c VK0No.29ï<ÎKÐV PQ¦øäÖA,A 4 K Bc+ò) PQÎU{!67}78dB4 ?0ò ) !62}75dB4 `7cò) PQÎU{!= æÂü(vLG +0=æ15m «s4!2* «+1* «[?  ̈ KÙ6S020m «¥|=æ4!ÂÆ, 67 #G`7cPQ¦ø ö A¥|0ï<Î=æ A 1: öõ|A N

Noise Reduction Experiments of Gabion Mattress in Drop Structure of Water-Cushion Type