(Full Paper) draft Water Trap Series as Integrated Approach.doc

8/11/2019 (Full Paper) draft Water Trap Series as Integrated Approach.doc

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Water Trap Series as Integrated Approachin Flood and Drought Protection and Adaptation

(Case Study of Mbay City, Aesesa District, age!eo "egency, TT Pro#ince$

Susilawati11Department of Civil Engineering, Faculty of Engineering,

Widya Mandira Chatolic UniversityU!"#$ %&''&, #((

)#D*#ES)"E+mail srsusipi-yahoo.com

Abstract:Mbay city has a unique area that consists of three parts : hilly, urban and rice field plain.The hilly part being highly deforested and eroded brings sediment to the lowest part: urban and ricefield plain. This causes flash floods and inundates urban area for quite a long time during rainyseason. An integrated approach is extremely needed to solve this situation. The concept of Ecodrainage that is how to channel away the flood water to the sea and how to manage the runoff water

and use it during the drought season could be the solution. The water trap series which are placedalong the drainage gullies could slow down the runoff water, and as such the water has a greaterchance to infiltrate to the soil as groundwater recharge. This means that Ecodrainage alsorepresents flood control and protection against and adaptation to drought by conserving this runoffwater and using it during drought situation.

Keywords: Eco-drainage, groundwater recharge, water trap, deforestation, erosion

1. IT"%D&CTI%

M/ay city has an uni0ue area that consists of three parts i.e. hilly on the upstream part, ur/an plainand rice field plain Fig. 12. (he hilly parts /eing highly deforested and eroded /rings huge sediment

to the lowest part i.e. ur/an and rice field plain. When the rainfall comes it causes flash floods whichinundate ur/an area for 0uite a long time /ecause the ur/an plain is covered /y alluvium sedimentthat form an impervious layer.

Figure ' Satellite iage of Mbay City

3ice Field plain

)illy parts

&rban settleentplain

Sea
mailto:[email protected]:[email protected]:[email protected]


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Ur/an plain often has flood pro/lem during rainy season. (hat happens /ecause of deforestation onthe hills causing the water to flow directly to the ur/an area without any drainage that channels therunoff to the sea or prevents if from gushing into the paddy field area downstream. Ur/an plain areaalso has drought pro/lem during the dry season /ecause of no ground water recharge during rainyseason, so the dug wells dry out. (riggered /y these flood and drought challenges that happen time

and again, we thin4 it necessary to develop a water trapped system to cope up with and to overcomethis situation, especially the one that ta4es place in M/ay.

(he main pro/lems of this area are 12 how to cope with the flash flood and drought disasters thatfre0uently happen, causing losses /oth in the ur/an area and in the rice+field area5 '2 6ow todevelop an integrated and sustaina/le system to cope with these flood and drought pro/lems whichincludes the idea of environmental conservation.

*+ FAS) F%%D AD D"%&-)T DISAST."

*+'+Defnition o Flash Flood and Drought Disaster

Flash flood, as far as ur/an area is concerned, is defined as an inundation of ur/an area during acertain period of time with a certain depth that hampers daily activity which inflicts a financial loss.While drought disaster is defined as or refers to the fact that daily water re0uirement to support dailylife cannot /e fulfilled. )n agricultural area, however, flood is defined as an inundation of agriculturalfield during a certain period of time with the certain depth, rendering the reduction of agriculturalproduction or even death of crops. While drought disaster is defined as the fact that crop waterre0uirement which support the optimum process of crop production cannot /e fulfilled, causing thereduction of agricultural production or even the death of crops.

Small islands which are surrounded /y the sea generally have limited ground water resources andare vulnera/le to flood disaster or tsunami. (he ground water in small islands is formed as floatinglens on the /rac4ish water or salt water, where its depth depends on the recharge. (his ground water

lens is also vulnera/le to sea water intrusion 6ehanusa, 17%82. Fal4land '99'2 gives somedescription a/out ground water /alance which has fresh water lens for coral reef island Figure '2.For the hilly island, the rainfall will flow rapidly as water runoff to the sea, so it has no chance toinfiltrate into the soil as ground water recharge. )t will cause limited ground water reservoir theamount of which is insufficient to fulfill the re0uirement that causes drought disaster. (he surfacerunoff that flows rapidly into the sea also causes flood disaster for the downstream plain. (hat is thecondition of small islands. :ecause of their small si;e we need to develop a rainwater managementso that it will not cause flood as well as draught disasters.

Figure *The ground /ater balance /ith fresh/ater lens on typical coral reef island(Fal!land, *00*$


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*+*+Several Factor Causes Flood and Drought

Factually, determinant factors that cause flood and drought are e


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water trap. (he research area is limited in M/ay plains which /ecome the location of case study

"gus Maryono, '99&, in his /oo4 on how to handle flood, drought and environment mentions fourmain methods of handling flood. (he four methods are

1. Massive reforestation in river /asins /oth in the forest area and in the settlement, in rural as wellas in ur/an areas. (his reforestation cannot /e delayed /ecause deforestation has /een rampantnationwide and has gone /eyond tolera/le limit. (he e ecology.

'. Strengthening the rivers> retention of flood. (his means that the flood is spread out along the riverfrom the upstream to the downstream. "s such instead of allowing a huge flood to ta4e place in aparticular spot, we create a condition that allows smaller and shorter floods to ta4e place alongthe river /asin. :eside wea4ening the flood, moderate overflow would /enefit the river>s ecologyand is needed to conserve water upstream and along the river. (he conse0uence of increasingthe river>s retention capacity is to refrain from /uilding di4es, ma4ing connecting passages/etween canals, and corro/orating the river/an4s, /ecause these methods will wea4en the

river>s capacity to resist flood along the gully. Moreover these will cause a huge flood to ta4eplace in a particular place especially in the downstream where the water flow is faster. (hereforethe method of ma4ing water par4ing lots along the river/an4s is recommended. (he greater thenum/er of water par4ing lots the smaller the chance of flood occurrence will /e.

. )ncreasing the num/er of retention ponds in all places in the plantation, in the farming area, inthe office area /oth in ur/an and in rural areas. (his retention pond that /ecomes a conservationpond should /e sociali;ed to all social strata and to government /ecause this method canprevent flood in the upstream significantly. Conservation pond can /e made with a simple method/y digging holes in the lowland. (his can /e affected through a policy of o/liging any new houseto ma4e a conservation pond in the /ac4yard of the house, so that the rainwater from asettlement does not flow directly to the river, /ut is stored into the conservation pond anda/sor/ed into the soil as groundwater conservation. (his method /ecomes a total correction

against the old method of areal corro/oration in order to 0uic4ly channel the water into the river?. (he /uilding of socio+hydraulic character or water culture. Socio+hydraulic character /uilding is

an approach to solve the pro/lems of water, environment, and flood /y enforcing a socialawareness of water in society. )f the social /ehavior is already correct towards water and itsecological components, then the solution of flood and environmental pro/lems will /e easier. "ssuch counseling, dialogs and education is necessitated.

*+2+ Concept and Strategy of .co3Drainage

Contrary to the concept of conventional drainage where the /asic idea is the physical strengtheningof an area, Eco+drainage is an integrated concept of sustaina/le development. :ased on this

principle, development of drainages is not only meant to channel the rainwater, /ut to contri/utepositively to social, economic and environmental aspects. (he /enefits of Eco+drainage other thanflood prevention are that

a. )t increases the 0uality of standard water/. )t /ecomes recharge for groundwaterc. )t develops recreation spotsd. )t supports economic activity, ande. )t evaluates the implementation of spatial planning.

(he conventional drainage is /asically in the form of conveyance. )n conventional drainage Figure 2the whole rainwater that falls on a particular place must /e channeled into the river as soon aspossi/le, and further to the sea. (his will result in the fact that groundwater deposit decreases in sucha way that it will cause drought disaster in the future.


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Figure 1+The concept of con#entional drainage(Agus Maryono, *004$

*n the contrary the concept of Eco+drainage is how to manage the surplus water /y not immediatelychannel it to the sea /ut to percolate it to the soil as a recharge for groundwater. (his can /e done invarious methods "gus Maryono, '99&21. Conservation pond method. Figure ?2 What is done is ma4ing water ponds in ur/an area, in the

settlement area, in farms and in plantation. Conservation pond is made to store rainwater /eforepercolating it into the soil while the rest is channeled slowly into the river. Conservation pond ismade /y utili;ing topographically low areas, e< sand mining location, and other a/andonede


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/e noted that the a/sorption well is specifically meant for rainwater so that the people around thearea should /e notified not to put gar/age into it.

Figure 4"ain/ater conser#ation /ith Absorption Well(5PPT, '666$

. 3iver side polder method. (his is a method of retaining flowing water and managing the rainwater surplus

Figure 7

"i#er Side3Polder in the upstrea and centralareas (Agus Maryono, *004$

)n the management of an integrated and environment+conscious drainage eco+drain2 we developstrategies how to implement and develop it. (he strategies are as follows

'+ Fro the source strategy

(his strategy concentrates on the source that /ears drainage pro/lems and how to prevent them.(he application of this strategy on a ;onal scale is nothing /ut an approach of rain management thatminimi;es the si;e of impermea/le area through a drainage which is made in resem/lance of itsnatural condition. (his will /e more economic and more esthetical and technically /etter. (hisconcept is /ased on the following principles.

a2 That e#ery 8one is part and parcel of a ri#er basin.

3elated to eco+drain,the handling of drainage pro/lems would /e most effective if it is made on a;onal scale which is part and parcel of a river /asin. "ctivities in ;one management are part of apreventive approach.

/2 5eginning fro the source.

When the rain falls on an area, gravitationally and in accordance with the land physics the waterpercolates into the soil. When the soil is covered with impermea/le material such as roof,


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concrete, or asphalt the rainwater will find its way to lower areas where together with otherwaters they ma4e runoff. )f the runoffs are collected in a pipe or a long canal /efore treatment, itis 0uite possi/le that along the waterway the water 0uality will decrease. (he strategy of end ofpipeG such as the construction of /ig retention ponds will /e more comple< and costly comparedto the >from the source> strategy. (he strategy with a small storage and simple treatment, which is

located on a place where all runoffs meet is to /e repeated consistently for the whole proBect.(his will preserve the water 0uality with a low cost. )f the runoffs are retained or percolated intothe source area, then

('$ )t will /e less e


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disaster management activities. )n an emergency of water pollution, sedimentation and the piling upof water gar/age, the handling strategy is from downstream to upstream with the o/Bective of waterrecovery.

2+ Solution tryout, cost sa#ing and adapti#e and sustainable anageent+

(he e


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Figure : "eclaation of -ulliesaccording to ;ale!ye syste(Mutunga et+al, *00'$

2+ DISC&SSI% AD C%C&SI%

4.1. Discussion

Untu4 studi 4asus M/ay, pende4atan sistem Be/a4an air untu4 mengatasi masalah /anBir dan4e4eringan secara terpadu dila4u4an /erdasar4an 4onsep Be/a4an air secara /erantai yangditempat4an pada alur drainase alam primer, se4under dan tersier. !enempatan leta4 Be/a4an air/erantai ini ditentu4an dengan mengguna4an model sistem pendu4ung 4eputusan Decision SupportSystem2 J DSS+M/ay Drain yang di4em/ang4an sesuai dengan situasi dan 4ondisi dari daerah studi.

Wilayah studi di/agi dalam ? unit sistem area yang di/eri nama M/ay iri, M/ay anan, M/ay

(engah dan M/ay Empat. Dengan mensimulasi4an setiap unit sistem area yang mema4ai programDSS+M/ay Drain, ma4a dapat ditemu4an leta4 Be/a4an+Be/a4an air /erantai water trap series2.=e/a4an air /erantai yang ditemu4an terse/ut dileng4api dengan data luasan daerah tang4apanhuBan Catchment "rea2 dimana potensi air huBan yang dapat di4endali4an dengan meresap4annya4e dalam tanah dapat ditentu4an pula.

Se/agai contoh simulasi diBelas4an dalam $am/ar 7, 19 dan 11 /eri4ut ini. $am/ar 7 menunBu44anlayout leta4 Be/a4an air /erantai dengan catchment areanya pada alur drainase alam primer padasistem area M/ay iri. $am/ar 19 menunBu44an layout leta4 Be/a4an air /erantai dengan catchmentareanya pada alur drainase alam se4under M/ay iri, sedang4an $am/ar 11 menunBu44an hal yangsama pada alur drainase alam tersier M/ay iri.

4.2. Conclusion

Dengan mengem/ang4an sistem Be/a4an air /erantai, ma4a air limpasan permu4aan yangmenye/a/4an /anBir dapat di4endali4an dengan memperlam/atnya. "ir limpasan yang diperlam/atdengan /angunan Be/a4an air /erantai ini a4an sempat meresap 4e dalam tanah, menBadi im/uhanair tanah groundwater recharge2 sehingga dapat mengatasi 4e4eringan yang terBadi di musim4emarau 4arena cu4upnya cadangan air tanah. Dengan 4ata lain, sistem Be/a4an air /erantai dapatmengatasi /anBir dan 4e4eringan yang terBadi, secara terpadu, /er/asis4an 4onservasi sum/er dayaair.


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Figure '' ayout 5angunan Infrastru!tur

(Full Paper) draft Water Trap Series as Integrated Approach.doc

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