Downstream O Ta Bet

A group of explorers set out to track the downstream path of the mighty O Ta Bet

As part of the downstream canal planning, and the FWUC organization, HT arranged for a group of us to meet and walk the entire length of the downstream O Ta Bet. The group included village chiefs, FWUC members, HT/CTO members, and EWB. As we walked, the village leaders explained where the stream flowed in relation to the Balang commune boundaries. They also pointed out how the water was currently being managed by the farmers - a system of man made dikes and diversions led the water from rice paddy to rice paddy quite effectively. GPS points were taken during the walk to trace the path of the O Ta Bet, for the purpose of canal planning in the future.

Chai, Sourneang, Sovann debating... should we have turned left at that tree back there?

At each twist and turn (or, after we had waded through a rice paddy where the water was knee deep) the group would take a short break in the shade to discuss where we'd been and where we were in reference to our map... and to check for any pesky leeches that were trying to get a free ride on our legs!

Following Bok Kron's sure-footed steps... and trying to move faster than the leeches.

As we made our way downstream, we stopped in to a crocodile farm whose owner has recently decided to take on relatively large scale dry season rice farming. Here, we saw what could become more commonplace in the future if more water is available during dry season. Water was being pumped from the stream to irrigate elevated fields of dry season rice seed. This was interesting to see, as we found out that the soil here absorbs water quite rapidly, and thus requires a large amount of water to remain irrigated - ie, placing large demands on the water supply during dry season.

Dry Season rice experiment at the crocodile farm: water pumping operating in the background. O Ta Bet is to the far right.

After having a rejuvenating glass of tea at the crocodile farm, the expedition continued downstream, finally making it to Bok Kron's daughter's house on the main road. Here, I got a glimpse into the rice harvesting process, and chatted with her family about the rice yields they were getting this year. Finally, our day completed with a homemade lunch and a de-briefing meeting where the FWUC and HT discussed plans for canal development and reservoir maintenance.

Prioritizing the canal construction with the FWUC

Even though 90% of the spoken conversation occurred in Khmer, I received translations from Chai, and it was good enough to get me through. I have to say, it was one of the most extraordinary days of my involvement on this project thus far.


Repairs & Current Work

Localized erosion

Basic repair items that are being addressed now are erosion along the downstream embankment in localized areas. Eroded areas will be backfilled and compacted, after proper surface preparation has taken place - removing grasses and leveling uneven and gullied soil. Erosion along the downstream wing wall returns will be filled in with rip-rap. Erosion has occurred here because it is exposed to foot traffic, fishermen who climb down the rip-rap along the side.

Erosion below Monitoring Well #4B

Each set of monitoring wells had an additional well installed at the downstream toe. Now there are four sets of three wells per set. This well will give a third plotting point on the phreatic line graphs, which we use to show the behavior of the water through cross sections of the embankment at four locations. The data will also help us in determining the most effective elevation to locate a toe drain just above the downstream toe.

As may have been mentioned at some point on this blog, there has been some leakage visible at the downstream embankment. We have monitored it visually and through the readings captured at the Monitoring Wells. For the last few months, the conditions have remained stable, which is a good thing, however it can't be left to leak for the long term. Our plans to plug the leaks have taken several twists and turns. The best case scenario for fixing the leaks has always included Bentonite, a naturally occurring clay which carries the unique inherent property that upon contact with water, it can swell up to 16x its original size. We would be using sodium bentonite in either powder or pellet form, and would spread it over the upstream embankment and insert it into potential inflow points to form a "plug" that would seal reservoir water from traveling through the embankment. However, Bentonite is not commonly used in Cambodia, and so we had to look elsewhere for material suppliers. We have just received pricing from a Thai supplier, and looks like we could receive material within two weeks. (PS, if any of our blog readers have information on bentonite suppliers in this region of the world, we would love to hear from you, for future reference.)

While this may solve the problem on our hands now, once the reservoir is fully turned over to the community, it will not be so easy to reach out to a Thai supplier, purchase material, and get it to the site... Something we're trying to start, as we perform maintenance and repairs on the embankment now, is getting the high level FWUC members involved directly. Participation of the FWUC is essential now, because they will be responsible for operating, maintaining, and inspecting the dam and watergate in the long term. A long period of overlap with EWB, HT, and FWUC all participating in routine dam inspections and monitoring procedures will help to ensure the success of the project's future management.


The Project

Looking North along the main embankment

Back in Siem Reap, and I must say it feels good to be here. I arrived about a week ago, after a whirlwind 17 day tour of Asia via the TransSiberian Railway (but that's another story, for another blog!) My last visit out here was in early 2008, in the very dry and dusty month of January.
Having just emerged from the rainy season, Cambodia seems like a different place in October - full of vibrant green colors, lush rice fields, tree limbs full of flowers and fruit, and the occasional afternoon or evening rain shower to cool the hot air.

I made my first trip out to the watergate early in the week, a day or so after I arrived. The first thing I noticed was that the ride to the site was surprisingly pleasant, and much quicker than I remembered... it took me just a minute to remember that the roads had recently been topped out and leveled by the military with laterite. What a difference! The second thing that I noticed was all the water flooding the rice fields, which I learned was from the reservoir. As Chai and I approached the watergate, again I was struck by the colors of the scene around me. The burnt orange of the laterite road, bright blue water in the reservoir, and the white/gray concrete of the watergate - it was quite beautiful. Chai and I walked the length of the main and north embankments, looking at the state of things in general after the past weeks of storms, and I reacquainted myself with the landscape.

I couldn't check out the Vetiver Nursery during my visit (due to the recent storms). The culverts on the south embankment are in good shape, and there were no worrisome wet areas on the downstream side of the embankment (though the water level is somewhat low right now, so none were expected). While at the site, Chai and I went through the latest version of the Operations, Maintenance, and Inspection Manual - a work in progress that is coming along well. I've been working with HT, analyzing some recently collected demographic and agricultural data from the villages surrounding the watergate. This information will be the basis of our Baseline Year Project Assessment. EWB's intention is to compare data over the next years of reservoir operation to see the impact that the project has had on the agricultural prosperity of the commune.

Structurally the embankment and watergate are in good shape. They weathered the recent storms very well, and that's encouraging for the future because Typhoon Ketsana was said to have been the worst storm to hit Siem Reap in years. Unfortunately, it seems that another storm is headed along Ketsana's path, Typhoon Mirinae. We'll see how things turn out as that storm develops.