I didn't spot how little support there was for おおかわ.  Anyway, even less reason to merge them.

Well, I'm rather certain it actually does have that reading (see 大河 【おおかわ】 Ookawa (p,s) in JMnedict), but Kojien, Daijisen, Daijirin, Wikipedia, Meikyo, and the various J-E dics all have only たいが, when it would have been quite easy for them to add it to their 大川[おおかわ] entries.  I'm tempted to just put all the usage tags on たいが, call おおかわ a name and delete it from here.

@@ -11,1 +11,2 @@
-<reb>おおかわ</reb>
+<reb>たいが</reb>
+<re_pri>ichi1</re_pri>
@@ -14,4 +15,0 @@
-</r_ele>
-<r_ele>
-<reb>たいが</reb>
-<re_pri>ichi1</re_pri>

http://dictionary.goo.ne.jp/leaf/jn/115837/m1u/大河/

http://dictionary.goo.ne.jp/leaf/jn/115837/m1u/大河/

Heading = Not match; Reading = Half-match; gloss = Match.

I think that's borderline for merging, I'd tend to keep them apart but add an x-ref

@@ -21,2 +21,3 @@
-<gloss>river</gloss>
-<gloss>stream</gloss>
+<xref type="see" seq="2560010">大川</xref>
+<xref type="see" seq="2560010">大川</xref>
+<gloss>large river</gloss>