PENGARUH GERAKAN TANAH TERHADAP LAHAN PERMUKIMAN Studi Kasus : Lahan Permukiman Jatisari, Kelurahan Pongangan, Kecamatan Gunungpati, Kota Semarang.

Abstract

Terjadi tiga ripe gerakan Lanai yaitu ripe nendatan, ripe rayapan dan tipe aliran, diswnping itu pengaruh gerakan tanah tipe nendatan terhadap lokasi lahan permukiman Jatisuri, clikategorikan dalanz tingkat sedang kuat, bahkan sangal kuat. Hal ini ditandai oleh degradasi lingkungan jisik dan kerusakan pada fisik bangunan, yaitu : (a) perpindahan massa lanall dan batuan pada mintakat deplesi, sepanjang lereng bukit dari ketinggian E +195 in nzenuju ketinggian yang lebih rendah E +140 in dpl, clan (b) rusak dan terputusnya jalan lokal sena saluran buangan, pergeseran clan runtuh total atau sebagian bangunan perumahan, retakan pada pondasi dun Binding bangunan runzah. Faktor penyebab terjadinya bencana aim gerakan tanah ripe nendatan antara lain : (a) topografi lereng bukit yang relalif curam, mencapai 80 % yang merupakan lokasi lahan permukiman; (b) litologi penyusun lerdiri dart tanah clan &thrall dart hatulempung dengan komposisi mineral lempung mommorilonit dan kaolinit, termasuk kelompok MH dengan bata• cair (LL) 63,70 %, indek plastisitas (P1) — 29,55 %, balers plas;is (PI) %, lifer pleads dan termasuk kelompok material ekspansif bila nzengandung air; (c) sebagian menmVukkan struktur kekar dengan kondisi apertur terbuka sedikit; (d) pada kondisi kering lapisan !anah dan batuan ini mudah pecah atau teijadi retaken: — retakan; (e) secara umunz permzikaein lahan dalam keadaan terbuka, lanpa iumbuh — tumbuhan penutup yang berfungsi sebagai pelindung perinzikaan. Sehingga pada musim hujan air permukaan langsung masuk hingga kedalaman tertentu clan menyehabkan perubahan sifat fisik, antara lain bertambahrzya volume dan beban yang dapat menyebabkan terjadinya ketidakstab flan lereng.ABSTRACT Semarang municipality, the capital city of Central Java, is also a metropolitan city. It has physically unique landscape because based on the morphology Semarang municipality is divided into two parts of coastal plain landform unit and range of hilly landform unit. In addition to people life distribution, almost 55% of population had settled in plain landform unit and 45%. in hilly landform According to services and the provision of housing for people, it has been determined that housing development is directed to increase the quality and quantity of affordable houses, appropriate with land use principle and also supported by adequate - infrastructures. The aim of this research is to .find out the level of integration in natural physical environment condition, potency and influence of natural hazard caused by mass movement in range of hilly land settlements. The method used in this research is survey method and extended with descriptive method Data analysis and evaluation are conducted through the utilization of morphogenetic threshold approach, threshold area approach, and land settlement suitability. Jalisari land settlement in Kelurahan I'ongangan, Kecamatan Gunungpati as location research is observed because it has had mass movement natural hazard. Based on the result of morphogenetic threshold approach analysis, Jatisari land settlement are divided into four threshold rating consisting : (a) threshold rating of 21 — 26, (b) threshold rating of 26 — 49, (c) threshold rating of 51 — 69, and (d) threshold rating of 72 — 86. Based on threshold area approach analysis, Jatisari land settlement are divided into four land classes : (a) very weak land especially on denudational slope of hilly landform, in part of river cliffof•K. Kripik..with composition of claystone of 0,26. acres; (b) weak land class usually found from top to downward of denudational slope of hilly landform without covered vegetation with composition of claystone of 2,16 acres; (c) medium land class usuallly with covered vegetation; with composition of claystone o f 2,20 acres; and (d) strong land class in part of plateau landform unit with composition of •,sandstone 1,12 acres.. Based on physical criteria the land settlement suitability is determined into : (a) slightly to steep slope land with 7 % --- 70 % steepness; (b) average rainfall 2374 mm per year; (c) soil classification is MN or Mediterrane soil with composition of clay mineral montmorillonite and kaolinite types, have potency to develop from middle to very high and have middle activity level; and (d) in pail of mass movement area, with total rating of phySiCal condition 17. It means that physical natural environment condition is not suitable for land settlement. Landslide of-Artisan land settlement has occurred into three types : (a) slumps or rotational slides, (b) creeps; and (c) flows. The influenced of rotational slide hazard on land settlement is classified into medium to strong level, even to very strong level, this condition is indicated by physical environment degradation and physical construction damaged such as (a) soil and rock mass displacement along hilly slope from E +195 m to E +140 m msl; and (b) destruction of local road, water channel, some part or totally collapse of house building, or wall and house foundation cracking. Mass movement hazard of rotational slide were caused by (a) topography with achieved steep slope 80 % as part of land settlement, (b) lithologically consists of soil and rock fragments of claystone with composition of montmorillonite and kaolinite clayminerals; including MK soil type with liquid limit 63,70 %, plasticity index 29,55 %, plastic limit 34,15 %; have plastic characteristic and classified as expansive material if wet or have water content; (c) half part showed crack or joint structures with slight open aperture; (d) in thy condition this soil or rock bedding is easy to fracture or cracking; (e) land surface is usually exposed without covered vegetation as surface protection. In rainy season part of surface water entered straight into certain depth of soil or rock bedding • and changed the physical properties i.e. increasing volume and weight of materials which could cause slope instability.