Hydrology in Chamcar Bei, an Assessment Of
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HYDROLOGY IN CHAMCAR BEI AN ASSESSMENT OF WATER AVAILABILITY FOR IRRIGATION PURPOSES HYDROLOGY IN CHAMCAR BEI AN ASSESSMENT OF WATER AVAILABILITY FOR IRRIGATION PURPOSES Dirk M. Eilander Tim H.M. van Emmerik Gert Mulder Marijn M. Piet April 2012 i Title Hydrology in Chamcar Bei; An Assessment of Water Availability for Irrigation Purposes Authors Dirk M. Eilander Tim H.M. van Emmerik Gert Mulder Marijn M. Piet Affiliation Delft University of Technology Faculty of Civil Engineering and Geosciences Department of Water Management Section of Water Resources Correspondence Stevinweg 1, k. 4.74 2628 CN Delft The Netherlands [email protected] Reference Eilander, D.M., Emmerik, T.H.M. van, Mulder, G., Piet, M.M., 2012, Hydrology in Chamcar Bei; An Assessment of Water Availability for Irrigation Purposes, available online at [www.hydrologycambodia.wordpress.com]. Keywords Hydrology, Cambodia, Water Availability, Ungauged Basins, Irrigation ii IN COOPERATION WITH: Bridges Across Borders Cambodia Engineers Without Borders Holland Samsam Water POWERED BY: HKV Lijn in water Deltares Wetterskip Fryslân Iv Groep Fonds Internationale Stages StuD iii Hydrology in Chamcar Bei iv Abstract Abstract In 2010 Bridges Across Borders Cambodia concluded that the Chamcar Bei irrigation scheme, southern Cambodia, is not functioning as it is supposed to. From February to April 2012 a hydrological study has been conducted, in order to formulate a framework in which further development of the irrigation system can be planned. Performing a quantitative and qualitative assessment of local hydrology has been the main goal of this study. In order to arrive at this, various elements of the Chamcar Bei catchment have been investigated. The catchment of study is a typical ungauged basin, meaning little to none (hydrological) measurements have been done. Therefore this study has used various alternative (and sometimes experimental) methods to generate the required data to make a hydrological assessment of the region. Since no accurate and recent maps of the area exist, mapping the area has been one point of attention. First of all, local topography has been studied. This showed that Chamcar Bei consists of three sub-catchments, which has functioned as the system boundary. Furthermore, an up to date inventory of the current irrigation system has been made. This showed that half of the gates are not functioning properly (e.g. broken, excessive erosion) and of most canals the end sections are shallow or overgrown by vegetation. For the total system an scheme irrigation efficiency of 45% was calculated. Given the crop calendar in Chamcar Bei a typical irrigation water requirement of 15 000 m3/year was found. To estimate several meteorological variables, different approaches have successfully been used. Precipitation was estimated with Kriging, using monthly data from 14 gauging stations, and TRMM, calibrated using monthly data from 2 gauging stations. Reference evaporation was estimated using Penman-Monteith using monthly minimum and maximum temperature from a nearby gauging station. Transpiration has been approximated using MODIS satellite imagery. Interception and soil evaporation were derived with a threshold method from daily TRMM precipitation. To estimate the potential for expansion of the irrigation system, two water balance models have been used. In one model, a historical water balance has been made. Assuming that on yearly scale the storage change in the soil is negligible, total annual catchment outflow has been determined for three hydrological years (April 2007 – March 2010). It was concluded that the Chamcar Bei catchment has a precipitation surplus, from which the total water availability for irrigation is equivalent to 67 typical hectares. The other approach a Rainfall-Runoff-Reservoir (Triple R) model was used to predict catchment runoff on monthly basis. This was used as input for a dynamic model of the irrigation system reservoir, with which several possible scenarios were evaluated. It was showed that at the current state, a maximum of 60 hectares can be irrigated. Enlarging the reservoir volume or applying more efficient irrigation techniques, this area can be increased to 100 hectares. Existing plans to build a new reservoir were evaluated as well. This showed that a new reservoir north of Chamcar Bei could provide at least 9 hectares with irrigation water. However, this number contains a high relative error, and more research should be performed to decrease the latter. Nevertheless it is advised to focus on improving the current irrigation system. By improving conveyance efficiency (e.g. lining canals, anti-erosion measures) or applying different irrigation techniques (e.g. dig furrows, different crops), a high quantity of water can be saved and applied on other lands. On several location throughout the catchment water quality test have been performed. Although insufficient parameters were measured to allow a definitive judgment on water quality, several conclusions can be drawn. Salinity tend to be no problem in Chamcar Bei. Iron, manganese, E.coli exceeds drinking water quality but no arsenic was found. More research on sodium, calcium, magnesium and potassium should be done to determine quality for irrigation purposes. Turbidity exceeds drinking water guidelines at all measured locations and might causes degradation of aquatic life on the long term. All results presented in this hydrological framework are considered to be of correct order of magnitude on a longer time scale (i.e. monthly and yearly). On a monthly scale it has been observed that various modeling results and assumptions corresponded with observed values from gauging stations. In both the historical water balance and the Triple R, several catchment characteristics were mimicked as observed in the field. Nevertheless the exact accuracy cannot be expressed. Predictions in ungauged basins remain an (highly) educated guess and only field measurements can verify the correctness of the proposed hypotheses. v Hydrology in Chamcar Bei vi Khmer abstract េសចក�ីសេង�ប េនក�ុងក ា ២០១០ ស�នឆុងកត់ារព�ដ�ម (Bridges Across Border Cambodia) ប�ន�ក�ិដ �� គេតរមាងស�សច�សពចំក (ChamcarBei) ែដលនិត� េនគាុកងុ្បូងៃន្របេ�មដ� ុជាមេនម ានដំ រពលប�ន�ក�ិដ �េនេនាះ ចប់ពីែខកុម�ចរហូតដល់ែខេម ងក ា ២០១២ ករសករសកផ�សធនដរ ស�ស�ម ប�េេធ�េឡងេដម្បីបង�េ តំែរនប ខ័ណ�មួយែ�ុេនេងចនាះករអភិវឌ្ឍ្របព័ន�ធារ���ស�បែន�មអុ េធ�េឡងះ ករសក្សោវយតៃម�ែបបគ និងបរិមាណេទេលធារស�ស�ក�ុដ �ប�ងឆេេម េដលេដងលដស្�ងចន�កេ�េះ េដមកី�នឲ្យដល់េគាលេ សមាសធាតសេុ្សងៗគា�ៃន ទឹកចំករបីេនះ្រត�វបានេធ�ករពិនិត្យ អងស�ក់ទឹកែដលសិក្ស គឺជាអង�ន�េដធម�ជាតិ ដ���េេធ�ករវស់ែវ េិយសរករវស់ែវង (ធារស) មិន្រត�វបានអនុវត�េឡ េហតុដូេច�ះ េហយ ករសិក្សោេនះបានេ្របេកសធន� ិធីសវ (និងជូនកលេ្រប្របេកសធនរេេធម់�េសេ�� ិេស ស�ស) េដម្បីបេង�តទិន�ន័យែដល្រត�វករស្រមាប់េធ�ករវយតៃម�ែផ�កធារស�ស�របស េិយសរែតមិនមានែផនទីជាក និងថ�ីៗៃនតំបន់េ�េ ករេធ�ែផនទីតំបន់េនះបានក�យេទជា មួយែដល្រត�វយកចិត�ទុកដះ ជាដំបូ ឋនេលខមូលដ�ន្រត�វបានេធ�កះ ករសក្សោេ� ំ ង � � ចំករបីេនះមានអងស�ក់ទឹកតូចៗច ៣ ែដលបានបេ្រមជា្រពំែដនរបស់្រប ជាងេនេេ េនៀក រហូតមកដលេ់លេ�េ ំ�� កសរេពភណ�ៃន្របព័ន�ធារស��ំ�កតក�មប�្រត�វបានបេង ករសិក េនះបង�� ចំនួ�ពក់ករ ល្�ៃធ ចន�រទឹកមិនទន់មានដំេណករ�សរ �លេន (ឧ. ខូច ហូរេ្រច ខ �ំងេព) េហយេនចុង្របឡាយទឹកភាគេ្រចនមាន ឬ មានរ�ជាតិក ដុះេ្រចនេលសល នតរមា ្របព័ន�ទំងល ៤៥% ៃន្របសិទ�ផលរបស់គេ្រមាងធនស�សរ �្រត�វបានេធ ទក់ទងនឹង្របតិទ ដំណាំេន�ុកាំ��ាងចំក ត្រម�វករទឹកស្រមាប់េ�សច�សពជាមធ្យម្រត�វបានរកេឃ ១៥ ៣ ០០០ដ /ងក ាះ េដម្បីវយតៃម�េលអេថរឧតុនិ មេក� ស�ស�េផ្សងៗ្រត�វបានយកមកេ្រប្របាស់េដ ក្រមិតទឹ េាឆ�ង្រត�វបានវយតៃម�ជាមួ Kriging េិយេ្រប្របាស់ទិន�ន័យ្របចំែខែដលទទួលបានពីស ទឹកេភ��ងចំនួន ១៤ និង TRMM េិយេ្រប្របាស់ទិន�ន័យ្របចំែខែដលទទួលបានពីស�នីយ៍វស ចំនួន ២ះ រំហួកេគាល្រត�វបានវយតៃម�េដយេ្រ Penman-Monteith និងសីតុណ�ភាពអតិបរ និង អប្បបរមា្របចំែខែដលទទួលប� �កិ្នរមុដសេនជ�កេនេះ រុក�បំភាយ្រត�វបា នបា៉រន េិយេ្រប្របាស់រូេ ចនំ MODISះ ករស �ក់ទ និងរំហួតរបស់ដីបានមកតមរមេកសធនរ� កំណត់មួយែដលទទួលបានពីក្រមិតទឹកេភ� TRMM ះ េដម្បីបា៉ន់្របមាណពីសក�នុពលស្រមាប់ព្រងីក្របព័ន�េ គំរូក�ល្យភាពទឹកចំនួនពីរ្រត�វបាន ្របាស េនក�ុងគំរូម តុល្យភាពទឹកជា្របវត�ិស�ស�្រត�វបានបេង� មានករសន�ិដ រស� េលម មា្រត ដ�ន្របច បែ្រមប្រម�លៃនក�កន�េនក�ុពក គឺមិនមានអ�ីគួរឲ្យកត់ស មា�លេេន េិយលំហូ vii Hydrology in Chamcar Bei ទឹកេចញពីអងស�ក់ទឹកសរុប្របចំឆា�ំ្រត�វបានកំណត់ស្រម ៣ងក ាផ � ស ធ ន រ (រែេដស ងក ា ២០០៧ ពល ែខមីន ងក ា ២០១០)ះ មានករសន�ិដ អងស�ក់ទឹកចំករបីទទួលបានម្រកិតទឹក បែន�ដ រពលតមរយៈេន លទ�ភាពរកបានទឹកសរុបស្រមាប់េ�ស គឺេស�នឹង ៦៧ហិកតជាមធ្ ស្រមាបេកសធន� រេស�េផ្សង គំរូអងបេង��រទឹកេភ�ុ (Rainfall-Runoff-Reservoir) (R ំក) ្រត�វបានេ្រប្ េដម្បីព្យោករណ៍ពីលំហូរទឹកេចញពីអងស�ក់ទឹកជា្រ គំរូេនះ្រត�វបានេ្រប្របាស់ជាធាត ស្រមាប់គំរូឌីណាមិចៃនអង្របព័ន�េ� េិ�កុងេនាះទិដ�ភាពែដលអចយកជាករបានម តក�មប�្ក្ដឆះ មានករបង�ញឲ្យ ស្រមាប់ស�នភា�ំ�ុប្ប ៃផ�ដីេ្រចនបំផុតរហូតដល ៦០ហិកតអចមានទឹកេ�សច�សព្រគប់ តមរយៈេធ�ករព្រងីកអ ឬ ករេ្រប្របាស់បេច� េងសច�សពកន់ែតមាន្របសល តំបន់េ�េគឺអចេធ�ករបមេ�នរហូតដ ១០០ហិកត ែផនករែដលមាន�សប់ស្រមាប់កស�ន�ថធកទតកថ�ីក៏្រត�វបានេធ�ករវ ចំណុចេ�េប� ំ ង � � អងស�ុកទឹកថ�ីែដលស�ិតេនខងេជងចំក�សរលចផ�ល់ទឹកេ�សចា ុក��ទ ៩ហិកត ែដរ។ ក៏ប៉ុែន� ចំនួនេ�េេនមានប��ក្រមិតខ�េនេេន េហតុេនះេហយករ�សវ្រជាវបែន�មគួរអនុវត�េដ កត់បន�យប��េនេពលេ្រកយេ េទះបីជា យា៉ងណាក មានករែណនាំឲ្យយកចិត�ទុកដក់េទេលករែកលម�្របព័ន�េ��ំ�ក េនះ។ តមរយៈេធ�ករែកលម�្របសិទ�ផលបែង�រទិសេដ (ឧ. ជីក្របឡាយទឹកតូ ដំដំណាំេុ្សង ) ទឹកែដលមានគុណភាពខ�ស់អចនឹងសន្សំបានេ្រចនស្រមាប់េ�សច�សសេទេលដ េនតមទីតំងជាេ្រច�ុុសនន�ៃាុដងល ករេធ�េតស�គុណភាពទឹក្រត�វបានអនុ េទះបី មិនប�េេធ�ករវស់ែវងឲ្យបានេពញេលញេដម្បីកំណត់ឲ្យច្បោស់ពីគុណភ ករសន�ិដ �នម ចំនួន គឺអចេធ�េទប ជាតិៃ្ គឺគា �នប��េនាះេទេនចំកះ ជាតិែដ ម៉ង់កែណ និងបាក់េតរីម� បរិមាណេ្រចនេលសពីទឹកស�តស្រមាប់ទ ក៏ប៉ុែន�មិនមានជាតិអេសនិកេនះ ករ�សវ្ បែន�ដេទេលជាតិសូងដ កល់សងដ រ ា េ � ាន ន ង ដ និងប៉ូតសងដ គឺ្រត�វេធ�េដម្បីកំណត់ពីគុណភាព ស្រមាប់េគាលបំណងេធ�ករេ�ស ជាតិល�ក់មានក្រមិតខ�ស់ជាងអ�ីែដលបានែណនាំទ ទឹកស�តស្រមាននសលៃ�េននដតគំនកនាុរពលប�្នននុ និងអចបង�ឲ្យបាត់បង់សត�ទឹកស្ រយៈេ់លែវង។ លន្សលទំងអស់ែដលបង�ញេន�ុគេតរុផ�សធនរេ�េ ្រត�វបានចត់ទុកថា្រតឹម្រត�វេទ លាេិ្�នទំហំស្រមាប់មា្រតដ�នរយៈេពលក (ឧ.