1,283 research outputs found

    Analysis of the hydrology of raised bogs in the Irish Midlands : a case study of Raheenmore Bog and Clara Bog

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    In the framework of the Irish-Dutch Raised Bog Project the hydrology of two raised bogs in the Irish Midlands, Raheenmore Bog and Clara Bog, was studied.The work focuses on relationships in the bog system and how they are affected by drain-age and turf cutting along margins. The concept of diplotelmy, a differentiation of the bog body into a shallow highly permeable top layer called acrotelm and a subjacent deep poorly permeable peat layer called catotelm, is followed. Some measuring methods yielded wrong results in bogs, so were modified to produce acceptable results. A novel field method to measure the transmissivity of the acrotelm was developed.The acrotelm behaves as an aquifer with a constant hydraulic gradient -the surface slope-and a transmissivity that is controlled by the phreatic level. The transmissivity increases by an order of magnitude when the phreatic level rises less than 10 cm and decreases as the level falls. Discharge varies accordingly. This mechanism and the large storage coefficient of the acrotelm ensure small seasonal fluctuations of the phreatic level (20 cm or less). Thus the acrotelm has a regulating effect on the hydrological conditions in a raised bog. Acrotelm transmissivity and -depth depend on surface slope. Well-developed acrotelms occur almost exclusively at surface slopes below 1%.The catotelm acts as an aquitard Downward seepage from Clara bog amounts to 5-10 mm a-1. The seepage from Raheenmore Bog is 10-15 mm a-1, in spite of differences of up to 3 m between phreatic levels in the acrotelm and piezometric levels in the mineral sub-soil.Water loss by horizontal flow in the catotelm is 1 mm a-1or less in both bogs. Thus the hydrological system of the bogs depends little on its surroundings. Turf cutting and drainage of bog margins directly cause surface subsidence over dis-tances of only a few metres from the margin. This results in a local increase of the surface slope. A steeper surface slope causes a reduction of the regulating properties of the acrotelm and thus a spreading of subsidence into the bogs. Because of the difference in composition of the peat in the centre and along natural margins, subsidence in the centre caused by internal drainage may be larger than along margins, causing watershed positions to shift to the margin. A prominent example is the convergent flow on Clara Bog towards the soak system of Shanley's Lough. Both are the result of subsidence caused by the road that bisects Clara Bog. Drainage on the bog destroys the acrotelm within a few years. Natural recovery of the bog ecosystem from such damage may take more than a century. Evapotranspiration from both bogs was 0.9 to 1.2 times Penman open water evaporation, depending on pre-cipitation in spring and summer.</p

    Gereguleerde ontwateringssystemen als middel tegen verdroging bij ontwatering van stedelijk gebied.

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    Bestrijding van grondwateroverlast in stedelijk gebied vindt in veel gevallen plaats door middel van ontwatering en daarmee gepaard gaande verlaging van de grondwaterspiegel. Dit laatste is ongewenst met het oog op de bijdrage aan verdroging. Men zal daarom een ontwateringssysteem bij voorkeur zo ontwerpen, dat aan de ontwateringseisen die voortvloeien uit de bestemming van het gebied wordt voldaan, zonder dat meer water wordt afgevoerd dan strikt noodzakelijk is. Verhoging van de ontwateringsbasis is daarbij een voor de hand liggende mogelijkheid. Dit leidt behalve tot een hogere gemiddelde grondwaterstand echter ook tot verminderde (grondwaterlberging en daardoor tot een toename van de vereiste ontwateringscapaciteit. In veel gevallen zal zo de afstand tussen de ontwateringsmiddelen onaanvaardbaar klein worden. Een alternatief is een automatisch gereguleerd ontwateringssysteem met diepe (tijdelijke) ontwateringsbasis, dat alleen werkt als er grondwater moet worden afgevoerd en zichzelf uitschakelt als dat niet nodig i

    Process for removing a small-molecule contaminant from a chlorine compound stream

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    The invention pertains to a process for removing a small-molecule contaminant from a chlorine-compound stream, the process comprising an adsorption sequence comprising the steps of (i) an adsorption sequence comprising the steps of - contacting a chlorine compound stream comprising a small- molecule contaminant with an adsorbent for the small- molecule contaminant, the chlorine compound being chlorine or chloromethane, said chlorine compound stream being in the liquid phase, and - withdrawing a purified chlorine compound stream from which small- molecule contaminant has been removed from the adsorbent, and (ii) a desorption sequence comprising the steps of - contacting the adsorbent containing small-molecule contaminant with a chlorine compound stream in the gaseous phase, and - withdrawing a chlorine compound stream comprising small molecule contaminant in the gaseous phase from the adsorbent, wherein the chlorine compound stream used in the desorption sequence is derived from the purified chlorine compound stream obtained in the adsorption section. The chlorine compound steam preferably is a chlorine stream or a monochloromethane stream. The small-molecule contaminant preferably is water. The process according to the invention allows the use of less equipment and gas streams, is flexible and avoids the introduction of additional contaminants

    Waterkwantiteit

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    Binnen het totaal van het OBN hoogveenonderzoek is dit hoofdstuk geweid aan het tijdreeksen-onderzoek van grondwaterstand en neerslag; het kwantificeren van waterstromen in zowel bestaande hoogveentjes als in regeneratiegebieden; het berekenen van een compartimentbreedte en afstand tot de (toekomstige) waterscheiding in de hoogveen gebiede
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